CEA/DAp seminar organization

Over its history CFHT has helped build or hosted dozens of instruments, operating from ultraviolet to mid-infrared wavelengths, attuned to Maunakea’s renowned observing conditions. One instrument, though, eclipses them all – MegaCam. It is in fact hard to imagine CFHT’s success today without the decisions made two decades ago to build what was then the largest digital focal plane in the world. MegaCam took engineering techniques to closely mount CCDs into a single camera to a whole new level. With its 1 degree field of view, MegaCam was able to tile the sky with images, creating rich and precise datasets on enormous scales that could be mined by the entire scientific community for decades. To date MegaCam has led to more peer reviewed science publications than all other instruments used at CFHT combined. It has been used to tune the model of Dark Energy and map vast regions of Dark Matter, unveil faint wisps of stars flung from interacting galaxies, reveal hundreds of free floating planets in star forming regions, and is currently directly contributing to a Stage IV dark energy measurement by providing the key ground-based photometry for the ESA Euclid space mission to derive photometric redshifts of hundreds of millions of galaxies over the northern sky. All of this is part of a revolution in wide field high-resolution optical imaging that CFHT pioneered for many years. Three speakers will offer a complete overview from technical aspects to the most impactful scientific result over these past two decades: - Stephan Aune (CEA, SEDI) - Design and construction by CEA Paris-Saclay - Jean-Charles Cuillandre (CEA, DAp) - Scientific operation at CFHT - Pierre Astier (IN2P3, LPNHE) - Supernovae and the Dark Energy equation-of-state

The evolution of a star is influenced by its internal rotation dynamics through transport and mixing mechanisms, which are poorly understood. Magnetic fields can play a role in transporting angular momentum and chemical elements, but the origin of magnetism in radiative stellar layers is unclear. Using global numerical simulations, we identify a subcritical transition to turbulence due to the generation of a magnetic dynamo. Our results have many of the properties of the theoretically-proposed Tayler-Spruit dynamo mechanism, which strongly enhances transport of angular momentum in radiative zones. It generates deep toroidal fields that are screened by the stellar outer layers. This mechanism could produce strong magnetic fields inside radiative stars, without an observable field on their surface. Magnetic fields generated by dynamo action appear as a process to trigger turbulence in stellar interiors. Depending on the parameters or initial conditions, we report different dynamo branches that could explain stellar magnetism and the rotation profiles observed for stars having a thick radiative envelope.

Le signal géomagnétique est une source riche d’informations sur la structure, la dynamique interne et l’histoire de notre planète. La production du champ magnétique Terrestre par effet dynamo dans le noyau externe implique une large disparité d’échelle spatiales et plus spécifiquement temporelles, s’étalant sur une gamme allant de l’année au milliard d’années. Depuis la mise en place d’observatoires magnétiques à la surface émergée de la Terre, l’attention s’est portée sur l’explication des variations à l’échelle du siècle, qui sont liées aux mouvements de convection dans le noyau. Depuis une vingtaine d’années, une couverture satellitaire globale et continue a cependant mis en évidence des variations de l’année à la dizaine d’années, dont l’origine est débattue. Ces nouvelles données ouvrent une fenêtre sur des phénomènes magnétohydrodynamiques rapides, de nature ondulatoire, en interaction avec la convection lente dans le noyau. Dans cet exposé, je présenterai les défis posés par la simulation conjointe des deux phénomènes ainsi que les avancées récentes et applications géophysiques potentielles.

In this talk, I shall review the most peculiar aspects of cosmology in the radio band, with a special focus on the SKA Observatory (SKAO). I shall present the main radio probes that can be exploited for late-time cosmology: continuum and 21-cm line galaxy surveys, neutral hydrogen intensity mapping, and weak lensing cosmic shear at radio frequencies. Furthermore, I shall present the most recent analyses of actual data from SKAO's pathfinders and precursors. Moreover, I shall discuss the added value of multi-wavelength synergies, presenting some show-case example of the power of radio-optical cross-correlations to test the foundations of the concordance cosmological model, such as the nature of dark matter and dark energy, or tests of inflation and gravity.

Code comparisons in cosmology are often performed with the underlying objective of identifying predictions upon which different codes converge that can be interpreted as robust, free of artifacts, predictions. Such an objective assumes that code comparisons can be constructed in such a way that the two notions of convergence and of robustness collapse. But, in order to achieve such a goal, code comparisons of structure formation have to meet an important epistemic challenge: that of constructing their codes ensemble on the basis of codes that are as independent as possible, but also comparable. In this talk, I show that enforcing the latter often amounts to multiplying common idealizations that hinder the achievement of the former, and thus leads to code comparisons that include many unscrutinized sources of artefacts possibly similarly distorting the predictions of the model. As a result, I argue that in context of high uncertainties where the domain of verification and validation of simulations has shrunk to code comparisons, code comparisons are better and actually very efficient as exploratory tools, both for getting insights into the physics implemented and for breaking the epistemic opacity of numerical simulations.

The evolution of interstellar dust reservoirs, and the evolution of galaxies themselves go hand-in-hand, as the presence of dust alters evolutionary drivers, such as the interstellar radiation field and the star formation history, while at the same time, the dust is being formed and altered by processes taking place in galaxies. However, far-infrared and submillimeter studies have revealed enormous dust masses at high redshifts that are difficult to explain with dust production from evolved stars (the so-called "dust budget problem"), while in the nearby universe there is also a significant mismatch between the dust production rate and the dust mass observed in the interstellar medium of galaxies. I will go over some possible explanations in an attempt to find a way forward towards a solution to this seeming discrepancy.

We perform first three-dimensional simulations of the magneto-thermal evolution using a spectral MHD code for crust confined magnetic field configurations. Our results show that presence of strong toroidal magnetic field in magnetars is necessary to explain their quiescent thermal emission, in particular a formation of a single hot spot. Using our thermal maps we are able to explain light curves of 10 out of 19 magnetars in quiescence. In the case of the central compact objects, we test the configuration of magnetic field formed as a result of stochastic dynamo. Such a magnetic field consists of multiple randomly orientated loops of magnetic field. Surface thermal map is becoming patchy and includes multiple hot and cold regions which are always observed simultaneously. The global dipolar field slowly formed as a result of the Hall and Ohmic evolution. In our simulations we see 5-10% pulsed fraction and difference of two times in temperature between hot and cold regions typical for observations of the central compact objects. We also study off-centred dipole configurations and found that they decay over time.

Over the past 5 years, we have made tremendous progress on both direct detections of the escape of ionizing radiation from galaxies, over a broad range of redshifts (and instruments), and the tests and validations of indirect probes of the escape of ionizing radiation from galaxies, both from observations and simulations. I will review these recent achievements, and describe the next steps to understand the nature of the sources of reionisation.

CHANG-ES (Continuum Halos in Nearby Galaxies — an EVLA Survey) is a project to observe 35 nearby galaxies that are edge-on to the line of sight to focus on their radio halos and the disk-halo connection. Wide-band VLA observations at L-band (1.5 GHz) and C-band (6.0 GHz) have provided opportunities to study in-band spectral indices, and observations in all four Stokes parameters with Rotation Measure Synthesis has led to a new understanding of the structure of kpc-scale magnetic fields in disk galaxies. This talk will highlight some of the results of the project and look to the future, as newly completed S-band (3.0 GHz) observations have filled in the L-band to C-band gap and led to the widest contiguous frequency coverage yet seen for galaxies.

Artificial intelligence (AI) holds more and more importance in our lives and in our work. While AI undeniably provides a smart and useful companion, the current debates of whether it may replace us altogether in our tasks highlights the role and importance of social interactions and emotions in the work environment at large. In this non-astrophysics seminar, I will present a recent study whose goal is to identify socio-professional (a.k.a. transversal, transferable, or generally "soft") skills that are critical in the transformation and innovation of companies/industries. As it turns out, most of these skills are actually acquired or at least strengthened throughout a career in fundamental research, including during the PhD. This is not surprising as transformation, innovation, but also breakthroughs, creativity etc... are common motivations in both worlds in which we seek answers to questions but we also seek questions themselves, within a complex environment and network of people. Many difficulties arise when dealing with soft skills, however: identifying them, acquiring and/or realizing they have been acquired, improving them, measuring them, making them valuable, and convincing other people they have been acquired. All in all, while most soft skills are well-known, the process of sorting, grouping, ranking them is necessary to set reference frameworks that can be acknowledged by most people. The purpose of this talk is to describe what soft skills are, how they are an integral part of research, and preliminary thoughts on how they can be applied/converted to non-academic world.

I will discuss recent breakthroughs in our understanding of galaxy evolution in the first billion years, including the impact of early galaxy growth on the (hydrogen) reionisation of the IGM. I will focus primarily on recent observational breakthroughs, especially with ALMA, VISTA, Subaru, HST and now (in particular) with the James Webb Space Telescope (JWST), but will also briefly consider the connections and tensions with theoretical predictions. I will endeavour to provide a balanced overview of this rapidly moving field, while highlighting recent advances that have been led from Edinburgh. Finally, I will consider the prospects for further improvement in our knowledge of early galaxy formation over the coming years.

Stellar feedback refers to the processes by which massive stars release energy, radiation and material into their surroundings, influencing the structure and evolution of the galaxies in which they reside. Understanding the impact of stellar feedback on different galactic environments is crucial for developing a comprehensive picture of galaxy formation and evolution. In this context, different galactic environments refer to regions within a galaxy that differ in their physical conditions, such as the average gas density, temperature, or metallicity. We study the respective impact of stellar winds, ionizing radiation, and supernovae in modern simulations of the multi-phase interstellar medium in parts of galaxies within the SILCC project, which I will present in this talk. From these galactic scale simulations we find that ionizing radiation is the most important factor in regulating the star formation rate, while supernova over-pressure the gas substantially, thus driving a galactic outflow.

Massive elliptical galaxies in the local universe appear to have their high-redshift analogs in the form of extremely compact quiescent galaxies. Therefore, it seems that compact star formation appears to play a pivotal role in the evolutionary pathways of massive galaxies across cosmic history. However, it remains to be understood what this role is in the broader picture set by the main sequence and the scaling relations in galaxy evolution. From an ALMA survey at 1.1mm, we reveal that compact star formation appears to be the norm in massive star-forming galaxies, and sizes as extended as typical star-forming stellar disks are rare. A population of galaxies with modest star formation rates, but which exhibit extremely compact star formation with starburst-like depletion timescales unveils. Compact star formation appears as a physical driver of depletion timescales, gas fractions, and dust temperatures. Gas and star formation compression seems to be a mechanism that allows to hold their star formation rate even when their gas fractions are low and they are presumably on the way to quiescence. Another population of galaxies missed in the deep optical surveys but bright at far-IR/mm wavelengths unveils thanks to recent JWST observations. We present a study investigating the drivers of dust attenuation in massive galaxies in the JWST-era, showing how the stellar mass and morphology plays an important role, with evidence for more compact stellar profiles resulting in the obscuration of galaxies.

Protoplanetary disks are the consequence of angular momentum conservation during the protostellar collapse. Their formation is a complex process which includes numerous physical effects (non-ideal MHD, stellar feedback, gas and dust interactions, turbulence…). In this seminar, I will present our recent works to better understand the formation of these disks. In the first part of the talk, I will focus on their gas content. I will show how modelling simultaneously the large scales of star forming regions and the small scales of protoplanetary disks allows us to constrain the statistical properties (mass, radius, temperature…) of these disks. The second part of the talk will be dedicated to the study of dust evolution. In particular, I will stress the consequences of this process not only for the formation of disks, but also for the formation of planets.

Le signal géomagnétique est une source riche d’informations sur la structure, la dynamique interne et l’histoire de notre planète. La production du champ magnétique Terrestre par effet dynamo dans le noyau externe implique une large disparité d’échelle spatiales et plus spécifiquement temporelles, s’étalant sur une gamme allant de l’année au milliard d’années. Depuis la mise en place d’observatoires magnétiques à la surface émergée de la Terre, l’attention s’est portée sur l’explication des variations à l’échelle du siècle, qui sont liées aux mouvements de convection dans le noyau. Depuis une vingtaine d’années, une couverture satellitaire globale et continue a cependant mis en évidence des variations de l’année à la dizaine d’années, dont l’origine est débattue. Ces nouvelles données ouvrent une fenêtre sur des phénomènes magnétohydrodynamiques rapides, de nature ondulatoire, en interaction avec la convection lente dans le noyau. Dans cet exposé, je présenterai les défis posés par la simulation conjointe des deux phénomènes ainsi que les avancées récentes et applications géophysiques potentielles.

With a new-generation of great observatories coming online this decade, unprecedented insights into exoplanets will soon be within reach. Observatories such as the James Webb Space Telescope (JWST) notably enable the study of atmospheres around terrestrial exoplanets and can reveal tri-dimensional structures in the atmospheres of their larger counterparts. Robustly leveraging new observations to reach such achievements will however require extra care as the models currently used may not be up to par with their precision. During this presentation, I will introduce work done by MIT’s Disruptive Planets group and collaborators towards supporting the robust in-depth characterization of exoplanets. I will specifically discuss how not accounting for the true shape of a planet can lead to a misinterpretation of its interior properties as well as atmospheric structure; how the current state of our understanding of light-matter interactions can similarly affect our interpretation of planetary spectra and thus inferences regarding their atmospheric properties; and how the current state of emission spectrum models for stars may even prevent from disentangling between the contribution of a planet and its host star, to start with. I will also present possible ways to address these challenges. I will end with a step-by-step roadmap to the robust characterization of temperate terrestrial planets with JWST, which includes habitability assessment.

The current Standard Model of Cosmology has successfully explained many phenomena, but it predicts that the majority of the Universe consists of dark matter and dark energy, whose properties are poorly understood. Because huge volumes collapse to form galaxy clusters, the largest known gravitationally bound structures, they are an ideal laboratory to study the Dark Universe. In fact, the ratio of baryonic matter to total matter in a massive cluster, fgas, can be considered representative of the matter content of the Universe as a whole. Measurements of fgas from the heaviest, dynamically relaxed galaxy clusters place powerful constraints on cosmological parameters as well as the dark energy equation of state. I will discuss constraints derived from fgas measurements using a multi-wavelength set of X-ray and optical data and provide outlook on the future of this measurement in the age of precision cosmology.

The Galactic Explorer with a Coded Aperture Mask Compton Telescope (GECCO) is a novel Explorer-class concept for a next-generation telescope covering the poorly explored hard X-ray and soft gamma-ray energies. This concept builds upon the heritage of past and current missions, improving sensitivity and, very importantly, angular resolution. GECCO uses the combined Coded Aperture Mask and Compton telescope techniques to employ the benefits of both: superior angular resolution provided by the deployable Coded Aperture Mask, and good background rejection and wide field-of-view (FoV) provided by the Compton telescope. It is being developed at NASA/GSFC in collaboration with other US and foreign institutions. GECCO observations will extend arcminute angular resolution to high-energy images of the Galactic plane, combining the spectral capabilities of INTEGRAL/IBIS and the x-ray imaging of NuSTAR and eROSITA, and will make a bridge to the Fermi-LAT observations, enabling a broad potential for discoveries in the MeV γ-ray sky. With the unprecedented angular resolution of the coded mask telescope combined with the sensitive, wide FoV Compton telescope, GECCO will focus on two main science objectives: a) Explore and resolve heavily populated sky regions, in particular the Galactic Center to resolve the nature and environment of the central massive black hole, to decipher the nature of its emission, such as the emission associated with the dark matter, new types of sources, or currently unresolved population of point sources. The GC long-term observation with ~1 arcmin angular resolution could be crucial in disentangling new physics in unexplored energy range. The Carina OB1 and OB2 associations, home to the most massive and luminous stars in the Milky Way, and Cygnus region, are other crowded places where high angular resolution is needed to resolve sources. b) Large FoV monitoring for transient events, detected with high sensitivity and accurate localization, performing multimessenger investigations to support GW and neutrino discoveries. Also, GECCO’s observational capability to disentangle discrete sources from truly diffuse emission and high energy resolution will contribute to understanding the gamma-ray Galactic Center excess and the Fermi Bubbles, and to tracing low-energy cosmic rays and their propagation in the Galaxy. Nuclear and annihilation lines will be spatially and spectrally resolved from continuum emission and from sources, addressing the role of low-energy cosmic rays in star formation and galaxy evolution, the origin of the 511 keV positron line, fundamental physics, and Galactic chemical evolution. Of special interest will be the exploration of sites of explosive element synthesis by conducting high-sensitivity measurements of nuclear lines from Type 1a supernovae and from other objects. The GECCO design is based on the novel CZT Imaging calorimeter, which serves as a standalone Compton telescope and as a focal plane detector for the Coded Mask. It also is a powerful tool to measure the γ-radiation polarization. GECCO’s octagon-shaped active shield also serves as a powerful all-sky detector of gamma-ray bursts, prompting the instrument to slew towards the burst direction and localize it with the Coded Aperture’s arcminute accuracy. GECCO will operate in the 100 keV - 10 MeV energy range, with energy resolution of ~ 1% from 0.5 - 5 MeV. The Coded Aperture Mask provides the angular resolution of ∼1 arcmin with a 2 × 2 deg2 fully coded field-of-view, while the Compton telescope provides the angular resolution of 3◦ − 6◦ with a 60 × 60 deg2 field-of-view. The 3σ, 106 s sensitivity is expected to be about 10-5 MeV cm-2 s-1 over the entire energy range. Primary mode of observation is fixed pointing, with extended exposure of the regions of interest. However, as a standalone Compton telescope with wide FoV, Imaging Calorimeter will simultaneously provide wide-area sky exploration, significantly broadening GECCO’s observational scope.

Thanks to an abundance of excellent observational data the evolution of the population of galaxies in terms of its stellar mass function, the distribution of star-formation across galaxies and their structural properties is known with good precision. The challenge we face, though, is to decipher the evolutionary paths of individual galaxies. Two roads to achieving this goal are 1) to reconstruct star-formation histories of individual galaxies through detailed modeling of high-quality spectra, and 2) attempt to define 'rules' for galaxy evolution that tell us how the collection of individual galaxies must evolve so that the population properties are reproduced. I will describe our recent progress along these lines, enabled by high-quality data from VLT spectroscopy of z~1 galaxies (the LEGA-C survey) and high-quality imaging data from HST (CANDELS) and JWST (CEERS).

The Sun’s large-scale magnetic field undergoes periodic reversals due to dynamo-action in the solar interior, through which the Sun’s magnetic field regenerates. The emergence of new magnetic field at the solar surface, after buoyantly rising through the convection zone, is clearly visible due to the formation of dark spots (sunspots). However, current models of the solar dynamo are unable to self-consistently capture the formation of sunspots, due to the range of pressure scale heights needed to include the photosphere. Thus, dynamo models remain disconnected from sunspot observations. The cyclic evolution of the Sun’s magnetic field also has a clear impact on the structure of the solar atmosphere and outflowing wind above. Similarly, linking the evolution of different scales, from the buffeting of convective motions in the photosphere to the dissipation of Alfven waves in the solar wind. Modern models of the Sun, therefore, require the combination of expertise from a range of interconnected subject areas. In this talk, I will highlight some of the recent work from the WholeSun ERC Synergy grant (https://wholesun.eu), which brings together expertise from five different host institutions across Europe. These works range from assessing the observational signatures of toroidal flux generation, to modelling small-scale energy injection at the base of the solar wind, and finally, estimating the large-scale variation in coronal structure and rotation during the solar cycle.

The millimetre part of the spectrum is one of the least explored parts of a galaxy’s spectral energy distribution (SED), yet it contains emissions from three fundamentally important physical processes. These processes are thermal emission from dust, free-free emission from ionized gas and synchrotron emission from relativistic charged particles moving in the galactic magnetic field. The NIKA2 camera (IRAM-30m telescope), observing at 1.15 mm and 2 mm, provides additional data points for input into the comprehensive SED models and allows us to: 1. disentangle spatially resolved galaxy SEDs from dust contribution, free-free and synchrotron emission; 2. constrain the evolution of the dust-to-gas mass ratio within galaxies, which provides a direct link to the chemical evolution of galaxies and the reservoirs for dust production; 3. study the microscopic properties of dust, i.e. constraints on millimetric opacity; 4. study the sub-millimetre excess in galaxies, whose origin is still unknown. These are some of the main objectives of the IMEGIN Large Program (Interpreting the Millimetre Emission of Galaxies with IRAM-NIKA2; PI S. Madden), targeting 22 nearby galaxies in the millimetre continuum regime with the NIKA2 camera. The millimetre data, combined with a suite of observations at other wavelengths, allow us to model the IR-to-radio SED and to put constraints on interstellar medium and dust grains properties of galaxies. We perform the galaxy SED analysis using the hierarchical bayesian fitting code HerBIE (Galliano et al. 2018), which includes the prescriptions from the dust evolution model THEMIS (Jones et al. 2017), anchored to the laboratory-measured properties of inter-stellar dust analogues. During my presentation, I will focus on the major challenges linked with data processing, uncertainty propagation, and large-scale emission filtering in NIKA2 maps (due to atmosphere removal during the data reduction process). I will show and discuss the latest significant results on NGC891 (Katsioli et al. 2023); NGC4254 (Pantoni et al. in prep.); NGC2976 and NGC2146 (Ejlali et al. in prep.); millimetre morphology (Nersesian et al. in prep.); future perspectives/applications.

The WST project aim to study and built an innovative 10-m class wide-field spectroscopic survey telescope (WST) in the southern hemisphere with simultaneous operation of a large field-of-view (5 sq. degree) and high multiplex (20,000) multi-object spectrograph facility with both medium and high resolution modes (MOS), and a giant panoramic integral field spectrograph (IFS). The ambitious WST top-level requirements place it far ahead of existing and planned facilities. In just its first 5 years of operation, the MOS will target 250 million galaxies and 25 million stars at medium resolution + 2 million stars at high resolution, and 4 billion spectra with the IFS. WST will achieve transformative results in most areas of astrophysics. The combination of MOS and IFS spectroscopic surveys is one of the key aspects of the project. It is very attractive because of the high complementarity between the two approaches. I will detail this innovative point using the example of the MOS and MUSE surveys performed in the CDFS region. The project aims to be the next major post-ELT project. It is supported by a large consortium of very experienced institutes plus ESO, representing 9 European countries and Australia.

Accretion of matter onto black holes often gives rise to outflows in the form of collimated relativistic jets and uncollimated winds. A deeper understanding of the launching mechanisms behind these outflows, manifesting in the form of blue-shifted absorption lines in the X-ray spectrum, can lead to valuable insights towards the behaviour of matter under extreme gravity. While low-velocity winds are considered to be ubiquitous in almost all accreting black holes, winds of relativistic velocities have been detected in a significant fraction of active galactic nuclei (AGN) over the last two decades. Out of the three prevalent wind-driving mechanisms (thermal, magnetic and radiative), these relativistic winds (also called Ultrafast Outflows or UFOs) could be launched by the latter two. However, a comprehensive investigation of the robust UFOs in Galactic black hole X-ray binaries (BHBs) has not yet been conducted in a systematic fashion, leaving a gap in our knowledge of the physics of black hole accretion across the mass range. In this talk, I will highlight our recent work in which we try to bridge this gap for the first time. In this work, we probe the magnetic driving behind the dense, non-equatorial UFOs in four BHBs with the NuSTAR, NICER and other X-ray observatories. We conduct detailed reflection modelling of the broadband X-ray spectra to measure the properties of the accretion disk and a direct MHD modelling of the absorption lines to determine the corresponding properties of the UFOs, thereby demonstrating an essential synergy between the reflection and absorption spectroscopy. The results of our study point towards a magnetic origin of UFOs in BHBs and hint that these low-inclination UFOs are necessarily supplemented with high wind and disk densities in order to be observed with current X-ray instruments. Such magnetically driven winds indicate a remarkable invariance of accretion and ejection processes over the very wide range of black hole masses, from stellar to super-massive. We anticipate our assay to be the gateway to more exhaustive future studies of UFOs in more comprehensive samples of BHBs and further exploration of magnetic wind driving in the JAXA/NASA’s XRISM era.

Fostered by upcoming data from new generation observational campaigns, we are about to enter a new era for the study of how galaxies form and evolve. The unprecedented quantity of data that will be collected, from distances only marginally grasped up to now, will require analysis tools designed to target the specific physical peculiarities of the observed sources and handle extremely large datasets. One powerful method to investigate the complex astrophysical processes that govern the properties of galaxies is to model their observed spectral energy distribution (SED) at different stages of evolution and times throughout the history of the Universe. In this talk, I will introduce GalaPy, a new library for modelling and fitting galactic SEDs from the X-ray to the radio band, as well as the evolution of their components and dust attenuation/reradiation. On the physical side, GalaPy incorporates both empirical and physically-motivated star formation histories, state-of-the-art single stellar population synthesis libraries, a two-component dust model for extinction, an age-dependent energy conservation algorithm to compute dust reradiation, and additional sources of stellar continuum such as synchrotron, nebular/free-free emission and X-ray radiation from low and high mass binary stars. On the computational side, GalaPy implements a hybrid approach that combines the high performance of compiled C++ with the user-friendly flexibility of Python, and exploits an object-oriented design via advanced programming techniques. GalaPy generates models on the fly without relying on templates, thus minimising memory consumption. It exploits fully Bayesian parameter space sampling, which allows for the inference of parameter posteriors and thus facilitates the study of the correlations between the free parameters and the other physical quantities that can be derived from modelling. The API and functions of GalaPy are under continuous development, with planned extensions in the near future. I will showcase the project and present the photometric SED fitting tools already available to users.

In this talk I report upon our results on the intracluster medium (ICM) of two clusters at the time when first clusters start to emerge from the cosmic web, z~2. Results are derived from new, high resolution, deep SZ and X-ray data providing us with the measurement of the two most distant resolved pressure profiles. IDCSJ1426 cluster at z=1.75 has a core whose properties are not far from the final stage, while the remaining part of the cluster is experiencing a sizable gas, heat and entropy transfer. JKCS041 at z=1.80 is caught just after a major merger event as evidenced by its SZ-X-ray peak offset, its low central pressure, and its low Compton-Y parameter compared to its WL mass. Comparison with plausible descendents shows that its ICM will experience major changes at all radii.

Inspired by the statistical mechanics of an ensemble of interacting particles (BBGKY hierarchy), we propose to account for small-scale inhomogeneities in self-gravitating astrophysical fluids by deriving a non-ideal Virial theorem and non-ideal Navier-Stokes equations using a decomposition of the gravitational force into a near- and far-field component. These equations involve the pair radial distribution function (similar to the two-point correlation function), similarly to the interaction energy and equation of state in liquids. Small-scale correlations lead to a non-ideal amplification of the gravitational interaction energy, whose omission leads to a missing mass problem, e.g., in galaxies and galaxy clusters. We also propose an extension of the Friedmann equations in the non-ideal regime. We estimate the non-ideal amplification factor of the gravitational interaction energy of the baryons to lie between 5 and 20, potentially explaining the observed value of the Hubble parameter. Within this framework, the acceleration of the expansion emerges naturally because of the increasing number of sub-structures induced by gravitational collapse, which increases their contribution to the total gravitational energy. A simple estimate predicts a non-ideal deceleration parameter qni~-1;this is potentially the first determination of the observed value based on an intuitively physical argument. We suggest that correlations and gravitational interactions could produce a transition to a viscous regime that can lead to flat rotation curves. This transition could also explain the dichotomy between (Keplerian) LSB elliptical galaxy and (non-Keplerian) spiral galaxy rotation profiles. Overall, our results demonstrate that non-ideal effects induced by inhomogeneities must be taken into account in order to properly determine the gravitational dynamics of galaxies and the larger scale universe.

The use of machine and deep learning is prevalent in many fields of science and industry and is now becoming more widespread in extrasolar planet and solar system sciences. Deep learning holds many potential advantages when it comes to modelling highly non-linear data, as well as speed improvements when compared to traditional analysis and modelling techniques. However, their often ‘black box’ nature and unintuitive decision processes, are a key hurdle to their broader adoption. In this seminar, I will give an overview of deep learning approaches used in exoplanet characterisation and discuss our recent work on developing Explainable AI (XAI) approaches. XAI is a rapidly developing field in machine learning and aims to make ‘black box’ models interpretable. By understanding how different neural net architectures learn to interpret atmospheric spectra, we can derive more robust prediction uncertainties as well as map information content as function of wavelength. As data and model complexities are bound to increase dramatically with the advent of JWST and ELT measurements, robust and interpretable deep learning models will become valuable tools in our data analysis repertoire.

In the classical picture of star and planet formation, disks are expected to form as a natural consequence of core collapse to form stars. Disks are then expected to mediate the extraction of excess angular momentum during the stellar accretion phase, and to be the locus of planet formation at later times. Reality is obviously much more complicated than this one line overview: disk properties “at birth” are a complex function of the star formation environment, the problem of transport in disks is far from being fully understood, as are the initial condition and timeline for planet formation. In this talk I will discuss some of these problems, mostly focusing on the successes and limitations of our understanding of the properties of individual disks and the global evolution of disk populations. I will discuss the current evidence for early planet formation in protoplanetary disks, and the open questions related to effect of the star formation environment across the Galaxy on disk properties and evolution, which likely also affect the planet formation process.

The origin of the heaviest elements is still a matter of debate. For the rapid neutron capture process (r-process), multiple sites have been proposed, e.g., neutron star mergers and (sub-classes) of supernovae (e.g., magnetorotationally driven supernovae). R-process elements have been measured in a large fraction of metal-poor stars. Galactic archaeology studies show that the r-process abundances among these stars vary by over 2 orders of magnitude. On the other hand, abundances in stars with solar-like metallicity do not differ greatly. This leads to two major open questions: 1. What is the reason for such a huge abundance scatter of r-process elements in the early galaxy? 2. While the large scatter at low metallicities might point to a rare production site, why is there barely any scatter at solar metallicities? We use a high resolution three-dimensional Galactic chemical evolution model to simulate the abundances of r-process elements and short lived (<100 My) radioisotopes over the lifetime of the Galaxy, in order to better constrain the site of the r-process.

Pulsar wind nebulae are fascinating systems, powered by the central rotating compact star, emanating a wind in the form of a relativistic, magnetized, and cold plasma that fills the nebula. They are visible as bright non-thermal sources in a very broad range of energies, from radio to gamma-rays. Observed morphologies vary with the evolutionary phase, with middle-aged and old systems strongly affected by the interaction with the ambient medium. Modeling of these sources requires some carefulness when going through the various phases, with a comprehensive description still lacking. Pulsar wind nebulae had been for a long time thought to contribute substantially to the positron excess in the CR spectrum at Earth -- potentially being the primary sources. In the last years, numerous evidence for efficient particle leakage by aged nebulae had been collected, showing up as quasi-monochromatic misaligned jets at X-rays in some cases, or in the form of extended TeV halos in others, reanimating somehow the interest in this class of objects. Here I will review our present knowledge of pulsar wind nebulae models through their different ages.

Solar Orbiter - ESA M1 Mission - has entered its scientific phase at the end of November 2021, after a cruise phase of more than 18 months (and 2.2 Billion km) and the commissioning of the 10 instruments on board. CEA/IRFU played a key role in this mission, by providing the focal plane detector array of the X-ray telescope, STIX, based on in-house Caliste technology. In the meantime, solar physicists have been busy preparing the pipelines needed to handle the data sent by the instrument, and developing high performance numerical simulations of the Sun. In this 2-voice seminar, we will relate the first 26 months of activities of the mission, covering both STIX calibration, its first light, the first solar flare detected, as well as the development of associated numerical simulations of the Sun and optimal scientific processing of instrumental data sent as the spacecraft gets closer and closer to the Sun (last perihelion was on 26 March 2022 at 0.32 AU), while in the meantime our star is increasing in intensity and in activity, with solar magnetic cycle 25 now well on its way.

In 2017 the work on the Comptonization (Sunyaev-Titarchuk) seen in the X-ray spectra of astrophysical sources was a candidate for the Nobel Prize in Physics. In this talk I provide all the details of the exciting prehistory of this topic and precise details of this discovery. The solution of this problem and its subsequent development and application to the spectra of accreting neutron star (NS) and black hole (BH) binaries reveals a lot of information on these objects. In particular, now we can unambiguously distinguish between a NS and a BH (Galactic or extragalactic) using correlations of their spectral indices vs mass accretion rate (or QPO frequency). I further demonstrate how we can determine a BH mass using this correlation.

The observed tight correlation between the star formation rate (SFR) and the stellar mass of star-forming galaxies (SFGs) is now well constrained over the last 10 Gyr of look-back time. This so-called main sequence (MS), whose normalization declines from z~3 to 0, is commonly interpreted as evidence that SFGs are evolving primarily through a steady and long star-forming mode, likely sustained by the cold gas accretion along the cosmic web. Over the last decade, a plethora of studies have investigated within this framework the physical properties of SFGs along and across the MS, establishing key scaling relations between, e.g., the stellar mass, gas content, and/or morphology of SFGs in the SFR-stellar mass plane. In this talk I will review past and recent observational evidences of this new MS paradigm and how it has shaped our understanding of the evolution of massive galaxies. Then, I will present the limitations of this simple paradigm, and in particular how it fails to explain the more diverse than anticipated population of MS galaxies (e.g., starburst hidden within the MS), the importance of secondary parameters (e.g., environment) and the transition of SFGs to quiescence. I will conclude by presenting future observational opportunities that can be used to investigate this hidden complexity within the main sequence and to further unveil the physics involved in the evolution of massive galaxies over cosmic time.

The Sino-French SVOM (Space based astronomical Variable Object Monitor) mission is ready for launch in 2023. This mission is dedicated to the study of Gamma-Ray Bursts and other transient and variable sources of the high-energy sky. On board SVOM there will be four instruments, ECLAIRs and GRM, with large field of views, operating in the hard X- and gamma-ray domain, and two narrow field instruments: the Visible Telescope (VT) and the Microchannel X-ray Telescope (MXT). The MXT is a novel kind of compact and light instrument based of the « Lobster Eye » optical concept, coupled to a low noise state-of-the art X-ray camera, the latter being designed and manufactured at CEA Irfu. For a total mass of 42 kg and a total power of 60 W, this instrument is composed of an optics system, a telescope tube in carbon fiber, a radiator, a camera and a data processing unit. The 9 kg camera consists of a focal plane assembly with a detector assembly and thermoelectrical coolers, a front-end electronics assembly, a calibration wheel assembly and a support structure assembly. We will first review the SVOM scientific objectifs and how MXT will contribute to reach them. Then we will present the MXT design in more detail, focussing on the CEA contribution, and finally we will present the results of the calibration campaign performed in 2021 before the delivery of the telescope to Cnes.

Starting from the largest scales, I will first describe how the cosmic web is woven across cosmic time into a gigantic bubble-like tapestry made of nodes, filaments, walls and voids. A particular emphasize will be put on the geometry and connectivity of this cosmic foam. Recent theoretical works aiming to precisely model the Universe on those mildly non-linear scales will be presented. In particular, I will identify a regime where large-deviation theory can be successfully implemented to predict the so-called count-in-cells statistics and describe promising cosmological applications for future galaxy surveys. The second part of the talk will focus on the birth and evolution of haloes and galaxies within these large cosmic highways. The highly anisotropic galactic environment set by the cosmic web will be shown to play a significant role in shaping them, an effect inducing large-scale galaxy alignments that are difficult to model but represent an important contamination for weak lensing experiments.

The impact of magnetic fields on the evolution and on the observational signatures of accretion disks is very uncertain. This uncertainty is mainly due to a lack of observational constraints on the magnetic field geometry or strength in accretion disks. However, even from a theoretical point of view our understanding of magnetized disks remains relatively poor. Indeed, analytic models of magnetized disks often need inputs from numerical simulations and numerical simulations of magnetized disks are difficult to perform and/or interpret. Because of this lack of magnetized disk models, standard disk models often reduce the magnetic field to a source of turbulence; turbulence through which the accretion can happen. While this simplification may hold for weakly magnetized disks, a large number of numerical simulations have shown that the role of a strong magnetic field goes far beyond producing turbulence. In particular, a strong magnetic field can produce powerful outflows, induce accretion through vertically elevated layers or non-axisymmetric structures, modify the time scales of accretion, enhance dissipation of gravitational energy in the disk and accelerate particles to very high energies. All of these effects dramatically affect the evolution and observational signature of accretion disks and open up new and exciting avenues to resolve outstanding problems of the standard accretion disk theory. In this talk, I will present an overview of my recent results on how strongly magnetized disks form, evolve and radiate. I will show in particular how strongly magnetized disks could explain events of very strong variability in AGNs, the flaring behavior of the Galactic center and the hardest emission in X-ray binaries.

De la scolarité aux postes à responsabilité de nombreux stéréotypes persistent qui souvent entravent la carrière scientifique des femmes. L’objectif de ce séminaire est d’identifier ces biais et de présenter des exemples de mesures concrètes pour y remédier et mettre en oeuvre des politiques d’égalité professionnelle entre les femmes et les hommes. Différents sujets seront abordés, tels que les critères d’évaluation, les actions de communication, le congé maternité et la parentalité, la lutte et la prévention contre les violences sexistes et sexuelles.

SKA is a new technology radio-telescope array, about two orders of magnitude more sensitive and rapid in sky surveys than present instruments. It will be able to detect and measure the redshifts of billions of galaxies at the redshifts up to z=2, to probe through baryonic acoustic oscillations the nature of dark energy; it will probe the cosmic dawn of the universe, just afer recombination, and during the epoch of reionisation (z=6-15); it will be the unique instrument to map the atomic gas in high redshift galaxies, and determine the amount and distribution of dark matter in the early universe. With SKA-VLBI, it will unveil the accretion and feedback processes near super-massive black holes, and results from precursors will be shown. We will discuss these exciting perspectives, which will concretize at the end of the decade.

Le laboratoire INTErnational d'Astrophysique des Rayons Gamma (INTEGRAL) a été lancé le 17 octobre 2002 de Baikonour (Kasakstan). Depuis lors il est resté sur son orbite elliptique de haute excentricité (environ 3 jours) effectuant 2568 révolutions (au 8 novembre 2022) autour de la Terre pour environ 530 Ms (méga secondes) d'observations scientifiques. Cette mission de taille moyenne transporte deux instruments principaux opérant dans le domaine spectral des rayons X durs et des rayons gamma mous (20keV-10 MeV), dont l'optique est basée sur le concept de masques codés : l'un est dédié à l'analyse spectrale fine avec des capacités d'imagerie modérées (SPI), l'autre est dédié à l'imagerie fine (ou presque) avec des capacités spectrales modérées (IBIS). Ces 20 ans dans l'espace sont le résultat d'au moins 15 ans de développement du projet avant qu'INTEGRAL puisse dévoiler le mystère du ciel à haute énergie. Le Dap a été profondément impliqué dans cette aventure de longue haleine, depuis le tout début du développement du concept de la mission (grande implication dans les deux instruments, ISGRI et SPI, participation au centre de données, développement de l'analyse s/w, suivi de la caméra) jusqu'à l'analyse actuelle des données en temps réel et des archives, avec un grand nombre d'articles publiés dans tous les domaines permis par les capacités instrumentales et même au-delà. Nous allons, dans ce séminaire, résumer ces plus de 35 ans en présentant divers aspects du projet/de la mission, en nous concentrant particulièrement sur ceux où l'implication du Dap a été cruciale. Nous commencerons par une vue d'ensemble de l'histoire de la mission, des principales caractéristiques instrumentales et des objectifs scientifiques au lancement, puis nous nous concentrerons sur la caméra ISGRI, la couche de détection 20-250 keV du télescope IBIS, qui est suivie au Dap tous les jours. ISGRI a été développée à l'IRFU et a obtenu la plupart des résultats d'INTEGRAL. Nous conclurons par un aperçu rapide et évidemment biaisé de quelques résultats scientifiques obtenus au cours de ces 20 années. Le séminaire sera présenté en Français avec des diapositives en Anglais par Philippe Laurent, Aymeric Sauvageon et Jérôme Rodriguez, bien humblement au nom d'un grand nombre de collègues anciens et actuels. ------------------------------------ ENGLISH VERSION INTEGRAL : 20 years in space and for a 35+ years adventure The INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) has been launch on October 17th, 2002 from Baikonour (Kasakstan). Since then it has remained on its high-eccentricity elliptical orbit (about 3 days) performing 2568 revolutions (as of Nov. 8th, 2022) around the Earth for around 530 megaseconds of scientific observations. This medium sized mission caries two main instruments operating in the spectral domain of hard X-rays/Soft Gamma-rays (20keV-10 MeV), whose optics is based on the concept of coded masks: one is dedicated to fine spectral analysis with moderate imaging capabilities (SPI) the other is dedicated to fine(-ish) imaging with moderate spectral capabilities (IBIS). These 20 years in space are the results of at least 15 years of project development before INTEGRAL could unveil the mystery of the high-energy sky. The DAp has been deeply involved in this long-term adventure from the very beginning of the mission concept development (large involvement in both instruments, ISGRI and SPI, participation to the data centre, development of the s/w analysis, monitoring of the camera) to the current analysis of real time and archival data, with a large number of published papers in all fields allowed by the instrumental capabilities and even beyond. We will, in this seminary, summarised these 35 years+ by presenting various aspects of the project/mission, focusing especially on those where the involvement of the Dap has been crucial. This will start with an overall overview of the mission history, the main instrumental characteristics and scientific goals at launch, followed by a focus on the ISGRI camera, the 20-250 keV detector layer of the IBIS telescope, which is followed-up at DAp every days. ISGRI has been developed at IRFU and obtained most of the INTEGRAL results. We will conclude with a quick and obviously biased overview of some scientific results obtained over these 20 years. The talks will be given by Philippe Laurent, Aymeric Sauvageon, and Jérôme Rodriguez humbly on behalf of many, many former and current colleagues and presented in French with slides in English. Local contact & organizer: Pierre-Antoine FRUGIER

Wherever we have the means of observing them, magnetic fields are detected across the full spectrum of astrophysical environments, from our own Earth, to stars, and cosmological structures. Magnetic fields are also present at all scales and evolutionary stages of star-forming structures. They have long been suspected to play a key role in shaping the typical outcome of the star formation process, such as stellar mass, spin, and multiplicity, or even the fate of stars towards their ultimate stages. In this talk, I will provide a global outlook on the progresses made in the recent years to characterize the role of magnetic fields during the embedded phases of the star formation process. Thanks to the development of observational capabilities and the parallel progress in numerical models capturing most of the important physics at work during star formation, the MagneticYSOs team successfully confronted detailed predictions of magnetized models to observational properties of the youngest protostars. I will present the physical processes and observational methods allowing to trace the magnetic field in embedded protostars, and review the main steps, success and limitations in comparing real observations to synthetic observations from the non-ideal MHD models. I will show how our work has shed light on the physical conditions required to ensure an efficient magnetic field coupling, and present unexpected results regarding the two main agents responsible for the coupling in star-forming cores: dust grains and ionized gas. Following this Ariane thread, I will argue our observational and theoretical findings support a novel scenario where the angular momentum problem for star formation may be actually “solved” not by the formation of large protoplanetary disks but by the combination of 1) lack of organized rotation motions at large envelope radii, 2) the inefficient angular momentum transport due to magnetic braking in the inner envelope (and angular momentum removed through rotating outflows generated by the presence of the magnetic field), and 3) a local origin of the angular momentum incorporated in the star–disk system. Reference review: https://ui.adsabs.harvard.edu/abs/2022FrASS...9.9223M/abstract

The launch of the JWST less than a year ago is expected to set a turning point in exoplanet science, which is progressively transitioning from detection and population statistics to in-detail characterization of the exoplanets’ atmospheres. In this talk, I will present an admittedly biased perspective of what this may represent for our understanding of exoplanets, and how ongoing theoretical work and future telescopes may build upon JWST’s legacy.

X-rays have unique advantages in studying absorption and scattering from interstellar dust. For example, sharp and deep absorption features of Mg, Si, O and Fe, which are the building blocks of silicates, fall in the X-ray band. Present X-ray observatories already delivered to us interesting results, challenging the common paradigm on interstellar dust chemical and physical characteristics. Future instruments will open up an unexplored window, revealing the most dense environments of our Galaxy. In this talk I will illustrate the state-of-art of our understanding of dust as seen in the X-rays, and future prospects, using for example, the upcoming XRISM satellite.

In the last 10-20 years we have been able to observe vast swathes of the Universe at different wavelengths, allowing us to build high-sensitivity maps of different projected cosmic properties. The statistical correlation between these properties and the density inhomogeneities that underlie the cosmic large-scale structures can then be used to reconstruct the spatial distribution of fundamental cosmological and astrophysical quantities, as well as their evolution in time. In this talk, I will describe a number of methods used to carry out this kind of tomographic reconstruction, present measurements of fundamental properties (structure growth, gas pressure, star formation rate density) resulting from their application to existing data, and discuss the potential of near-future "Stage-IV" experiments to improve on and benefit from these methods, in their quest to improve our understanding of fundamental physics.

Intensity Mapping (IM) has been proposed about 15 years ago as an efficient technique to perform cosmological surveys. The 21cm hyperfine transition of neutral hydrogen can indeed be used to map the 3D distribution of matter in the universe, over a wide range of redshifts, from z=0 to z=3 or even z=6, bringing complementary information to the optical surveys. Since then, few dedicated instruments have been built (CHIME, Tianlai, BINGO) to explore the feasibility of the method; Other more ambitious instruments, such as HIRAX, CHORD or BINGO will be commissioned in the coming years. Intensity mapping surveys are also envisaged for SKA, in addition to the classical HI source surveys. After presenting the principle of 21 intensity mapping, I will briefly discuss its cosmological promises, as well as some of the associated instrumental and scientific challenges. I will then present some of the results of ongoing observations, focusing on Tianlai, and on PAON4. Tianlai is an international project that operates two pathfinder instruments, a cylinder array and a parabolic array, built in Xinjiang, in western China. PAON4 is a small test interferometer, located in Nançay, used to explore some of the technical aspects of compact radio arrays, operating in transit mode.

The next generation of telescopes such as the SKA and the Vera C. Rubin Observatory will produce enormous data sets, far too large for traditional analysis techniques. Machine learning has proven invaluable in handling large data volumes and automating many tasks traditionally done by human scientists. In this talk, I will discuss how machine learning for anomaly detection can help automate the process of locating unusual astronomical objects in large datasets thus enabling new cosmic discoveries.

Cosmological simulations of galaxy formation are reaching a high level of accuracy and can finely reproduce some of the main properties of galaxy populations: stellar masses, angular momentum, colors, etc. However, most galaxy formation simulations still fail to account for the detailed structure of galaxies and their global star formation history. Using high-resolution, idealized simulations of galactic dynamics and star formation, I will show that these disagreements are not cosmetic details but point toward a fundamental tension between observations and galaxy formation models. Historically, galaxy formation models predicted galaxies with unrealistically large stellar masses: in modern cosmological simulations, this issue is generally solved though energetic feedback from young stars and supermassive black holes. I will nevertheless show that feedback, as implemented in such simulations, is generally excessive, leading to the early and unrealistic exhaustion of interstellar gas reservoirs. Comparisons to idealized simulations and observations of galactic winds support the conclusion that energetic stellar and black hole feedback cannot be entirely responsible for the regulation of star formation and galaxy growth. Other physical processes likely emerge from sub-galactic scales in the interstellar medium, such as subtle coupling between galactic dynamics and star formation through instabilities and turbulence. Nevertheless, some cosmological simulations can now successfully describe the re-distribution of baryons from galaxies to the intergalactic medium, and I will show that these simulations are a crucial tool not just for galaxy formation but also for modern cosmological surveys. I will finally review how simulations of galaxy formation, evolution and star formation could gain strength in the years to come, in relation with the arrival of exascale supercomputers.

Ariel est la mission M4 du programme ‘Cosmic Vision’ de l’ESA. C’est une mission entièrement dédiée à l’étude de l’atmosphère des exoplanètes ; un millier d’exoplanètes vont être scrutées. La France apporte une contribution majeure à cette mission en ayant la charge du développement de l’instrument principal d’Ariel : le spectromètre InfraRouge AIRS 2-8 microns. Ce développement se fait sous maitrise d’ouvrage du CNES et maitrise d’œuvre du DAp-AIM ; les autres laboratoires participants sont l’IAS, le LESIA et l’IAP. Dans ce séminaire nous présenterons la mission, ses enjeux scientifique et techniques avec un zoom sur la contribution française.

Selon Newton, la cause des mouvements des planètes et des comètes est la gravitation universelle qui crée les forces nécessaires pour que ces astres se déplacent sur des orbites elliptiques autour du Soleil. Il publie ce travail en 1687 dans sa grande œuvre les Philosophiæ naturalis principia mathematica, communément appelée les Principia. Très admirative de ces idées nouvelles, Émilie Du Châtelet traduit en français le texte latin des Principia dans le but de les diffuser. Son action n'est pas solitaire : Maupertuis, Voltaire et Clairaut notamment vont la soutenir dans sa lourde tâche, car plusieurs savants français n’acceptent pas l’idée d’action à distance que serait la gravitation. Après le décès d'Émilie en 1749, Clairaut devient l'éditeur du manuscrit des Principes mathématiques de la Philosophie naturelle, mais l’ouvrage ne sera publié que dix ans plus tard, en 1759. À l’occasion de la parution d’une nouvelle édition critique de ce livre, on reverra les apports fondamentaux de Newton, puis on regardera le manuscrit d’Émilie Du Châtelet et on verra le rôle de Clairaut dans la parution tardive des Principes et du Commentaire écrits par « l’immortelle Émilie ».

Besides the classic heralds of astronomy, from radio waves to X-rays, the past two decades have seen the emergence of four fantastic messengers: astroparticles. Gravitational waves, GeV-TeV gamma rays, PeV neutrinos, and cosmic rays at EeV energies and above are all now, since 2015, informants on the conditions prevailing in the most extreme accelerators that our universe houses. In this talk, I will illustrate the first steps of multi-messenger astronomy with gamma-ray and cosmic-ray signals that have traveled to our ground-based detectors from cosmic scales, ranging from the innards of our super-cluster, Laniakea, to a time when the universe was only a fifth of its current age, beyond z ~ 2. Astroparticles from the most extreme extragalactic emitters not only enable the probe of particle acceleration at energies beyond the reach of human-made facilities, but can also be exploited as tracers of the electromagnetic content of the universe. Magnetic and photon fields populating the largest voids in the cosmos are starting to reveal their mysteries, setting the grounds for the newborn field of gamma-ray cosmology and long-awaited cosmic-ray astronomy. Major astroparticle observatories are under upgrade or construction and they hold a formidable scientific potential for current and next-generation researchers.

Jet-driven core-collapse supernovae belong to the most energetic transients in the universe and are key targets for time-domain astronomy surveys. I will discuss the unique challenges in both input physics and computational modeling for these systems involving all four fundamental forces and highlight recent breakthroughs in full 3D simulations. I will pay particular attention to how these simulations can be used to reveal the engines driving these events and conclude by discussing what remains to be done in order to maximize what we can learn from current and future time-domain transient surveys.

Studies of 'nearby' molecular clouds - within a distance of a few 100 pc and with the Orion Molecular Cloud as the most prominent example - have revealed the physics of star formation in exquisite detail - ranging from density profiles of clouds from dust extinction mapping to accurate star formation rates from counting young stellar objects. Larger samples of clouds are needed to place these local results in a more complete context. The arguably best way to obtain a large reference sample of clouds would be to observe resolved individual molecular clouds in the Andromeda Galaxy (M31), as the most nearby large spiral galaxy with close to Galactic metallicity - importantly using dust rather than gas as the primary tracer, just as for the local clouds, enabling a direct comparison. Fortunately, with wideband continuum radio interferometers, this is now becoming possible. I will present first results of a large program targeting M31 with the Submillimeter Array (SMA). Using the SMA's wideband capabilities, we have not only demonstrated that direct detection of resolved continuum emission from individual clouds is now possible on scales of 10-15 pc in M31, but we can even concurrently measure CO within the same observational setup. This ensures identical calibration and spatial filtering of dust and gas measurements, providing unique constraints on cloud identification and the CO 'X' factor for a large number of molecular clouds. Given the meaningful overlap in physical resolution with measurements of local clouds, this experiment will truly enable us to compare the local molecular clouds with a significant fraction of the cloud population of the Andromeda Galaxy. The main goals of the project include a cloud-scale assessment of star formation laws as well as of cloud properties as described by Larson's relations.

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SPHERE is the new generation exoplanet imagers installed at the Very Large Telescope. Since 2015, we have started the large-scale SHINE survey to look for giant exoplanets around a sample of 400 to 600 young, nearby stars (younger than 300 Myr, closer than 150 pc). The main goal of SHINE is to constrain for the first time the population of giant exoplanets in the 5-100 AU range, where previous direct imaging surveys and other detection methods are not sensitive. After describing the SPHERE instrument and the astrophysical context, I will present the current status of SHINE, some of its recent discoveries and the first statistical constraints drawn after 4 years from a sub-sample of 200 observed targets. Finally, I will conclude with instrumental considerations by presenting some evolutions foreseen for the instrument over the next few years.

After a short introduction on ultra-high-energy cosmic-ray (UHECR) physics, I will discuss the implications of the recent Fermi-LAT data regarding the extragalactic gamma-ray background, as well as IceCube very-high energy neutrino data, for the origin of UHECRs.I will show how calculations of the diffuse flux of cosmogenic γ-rays and neutrinos, produced during the propagation of UHECRs in the extragalactic medium, can provide constraints on the possible cosmological evolutions of UHECR sources. I will present in more details the mixed-composition scenario considered in several papers by Globus et al. (which is in agreement with most UHECR data) and show that this model is compatible with both the Fermi-LAT measurements and the current IceCube limits. I will finally discuss the possibility for future experiments to detect cosmogenic neutrinos and further constrain UHECR models, including possible subdominant UHECR proton sources.

Both in the present-day Universe and earlier on, approximately z~3, we have documented profound structural differences between star-forming and quiescent galaxies. The former host their star formation in rotating disks (thinner and colder today, apparently thicker and hotter at high redshifts), the latter are predominantly dynamically hot systems and have spheroidal morphology, At high redshift (z>1) and up to when quiescent systems can be reliably identified (z~3-4), dynamical information becomes more uncertain, at least in passive systems, but this dichotomy seems to persist at least morphologically. Therecent discovery that disks at high redshift (22) have mostly focused on the growth of the core stellar mass density, e.g. at r<1 kpc. These very central volumes are the sink of all the dissipative processes that take place during star formation and while they inform us, in an integral way, on the accretion history of the galaxy of both the dissipative (gas, via cold and hot accretion) and non-dissipative (stars and dark matter, via adiabatic contractions) components, they are baryon-dominated even in today disks and do not contain information on if and how the large-scale structure of galaxies evolves, dark matter included. Here I show novel evidence that the large-scale spatial distribution of stellar mass (from rest-frame light at ~4000 to 6400 Ang), i.e. of one of the two non-dissipative components, of massive galaxies at 1.5

Local contact: E. Daddi, organization: M. Galametz

Comets are icy bodies remnants of the earliest moments of the solar system formation and that are now studied in details by space missions. The most recent spacecraft, Rosetta, has ended its studies in September 2016 after having landed Philae for the first time on the surface of a cometary nucleus and followed 67P on its orbit for more than two Earth years. The on-board scientific instruments have demonstrated the sporadic behavior of the cometary activity as a function of its orbital properties. Cameras have unveiled an irregular surface prone to erosion and deposition of dust, with few spots of ice detected on its surface. Dust particles detectors have shown that two types of solid particles are ejected by the nucleus, one being dense and compact grains and the other being very fluffy irregular dust particles. No specific structures inside the cometary nucleus were detected by instruments sounding inside the nucleus, and the very low density of the cometary material (0.5 g.cm-3) remains difficult to explain. Gaseous particles ejected by the comet contain a high fraction of O2 and complex carbonaceous molecules like glycine, an amino acid that was first detected in situ by Rosetta. We will review the results from the whole Rosetta/Philae mission and describe in details what we have learned about these objects.

Cosmic dust absorbs the optical/UV photons produced by stars and SMBH and re-emits the energy at longer wavelengths in the IR regime. Infrared observations are, therefore, crucial to achieving a complete picture of the star-formation density (SFRD) , and to understanding the properties of dust across cosmic time. Thanks to the latest IR Herschel satellite (2009-2013), a comprehension of the SFRD was estimated up to z~3-4, but recent observations in the sub-mm regime (SCUBA-2) show discrerpancies with previous Herschel results. I will discuss the possible reasons for this discrepancy and show the critical role that the IR SPICA will play in the future .

Space weather is extremely demanding in term of space data for solar, magnetospheric or ionospheric survey. Small satellites are interesting in the sense they are easier to build, cheaper and then accessible to new entities like countries without space history, SMEs and universities. Due to their lowest costs, they also can be launched in constellation for better spatial or temporal coverage. As a complex science dealing with a chain of phenomenon coming from the sun to the Earth through the magnetosphere, space weather can benefits from the multiplication of satellites. After an introduction based on the potentialities and constraints of cubesats, we will focus on two example, AMICal Sat and ATISE developed at the CSUG in Grenoble. We will then extend these example to explain why space weather is a priority application of the cubesats and give a large overview of the project in development.

The Maunakea Spectroscopic Explorer (MSE, formerly Next Generation CFHT) is an advanced project to profoundly transform the current CFHT into a survey telescope with a 10-meter mirror and a dedicated, heavily multiplexed, wide-field spectrograph with a wavelength coverage of 0.4-1.8 micron and multiple spectral resolutions. MSE is borne out as the response to the astronomical community's need for a large aperture, dedicated, spectroscopic survey facility in synergy with imaging surveys (LSST, WFIRST, ...) and giant telescopes (GMT, ELT, TMT). The project is now entering preliminary design phase after successfully completing its conceptual design. We will present the current architecture of the observatory as well as the expected performance characteristics of the project and describe the science that is driving this unique facility: unveiling the properties of the faint universe, whether they relate to the origin and diversity of stellar systems, Milky Way archaeology at the earliest time, galaxy evolution across cosmos times, or illuminating the dark universe. Finally, we will conclude with an overview of the project's partnership and organization.

Cold gas plays a central role in feeding and regulating star formation and growth of supermassive black holes (SMBH) in galaxy nuclei. Particularly powerful activity occurs when interactions of gas-rich galaxies funnel large amounts of gas and dust into nuclei of luminous and ultra luminous infrared galaxies (LIRGs/ULIRGs). These dusty objects are of key importance to galaxy mass assembly over cosmic time. It is also increasingly clear that feedback from star formation and AGNs is fundamental to regulating the evolution of galaxies in the nearby Universe as well as at earlier epochs. Mechanical feedback occurs in the form of winds, turbulence, supernova bubbles and superbubbles, AGN jets and backflows. There is mounting evidence that massive amount of cold molecular gas is being expelled from galaxy nuclei and starburst regions by the feedback process. With the advent of ALMA and the NOEMA telescopes we can now study the structure, physical conditions and chemistry of the cold flows and the dusty nuclei at unprecedented sensitivity and resolution. I will focus on recent ALMA and NOEMA studies of AGN and starburst outflows from dusty galaxies. I will, for example, present recent ALMA studies with resolutions of 20 milli arcseconds (2 – 7 pc) of the launch regions of molecular outflows and jets in the nearby LIRGs NGC1377 and IC860. These outflows are different from each-other where NGC1377 shows a 150 pc scale radio-quiet molecular jet (that appears to be precessing) while the IC860 flow is exceedingly compact and dense and appears to be in a young phase. I will also discuss observational methods that reach behind the curtain of dust in the most obscured centers of U/LIRGs , allowing us to undertake new studies of heretofore hidden, rapid evolutionary phases of galaxy nuclei.

Let's assume dark matter is a particle. The DM theories currently tested, either with direct or indirect detection, cover only a tiny range of the allowed DM parameters space. A new, viable, DM candidate, the Axion Quark Nugget (AQN), has been proposed by Zhitnitsky (2003), partly inspired by the quark nuggets (Witten 1984). In the AQN model, DM particles are very massive (gram mass) and interact very rarely, but very strongly, with the baryonic sector. They behave as cold dark matter, and yet are made of regular matter, without contradicting primordial nucleosynthesis. In this talk, I will review the basic properties of this model and some of its astrophysical successes obtained so far. I will then discuss recent work we have done on how this DM interacts with the solar corona and how the model can be more thoroughly tested in the future.

We will review the relevance of historical observations for current astrophysical problems, in particular for the reconstruction of solar activity in the 17th century Maunder Minimium and the pre-telescopic time - as well as the study of historical supernovae in our Galaxy. Among other observations, we will discuss the strong 14-C variation around AD 775 detected in trees around the world and discuss possible causes like a nearby supernova, a Galactic gamma-ray burst, a solar super-flare, etc.

Being complex systems containing vast amounts of gas, dust, and stars, galaxies allow us to study the Universe in great detail. It is inside these systems that stars form, and transform the simplest of elements, hydrogen, into heavy elements essential for life as we know it. In the last few years I have worked dissecting galaxies in an effort to obtain clues to their chemical evolution histories. Star clusters, both Globular and Young Massive Clusters (YMCs), are attractive test laboratories for several astrophysical reasons. Given that these objects can be observed and studied in detail at larger distances than individual stars, one can use them as tracers of stellar populations outside of our own Milky Way. Using spectroscopic observations of star clusters covering a broad range of ages (~2 Myr to ~12 Gyr) we probe the chemical enrichment history of the host galaxy. I will discuss recent work exploiting spectroscopic observations acquired with both the ESO Very Large Telescope and the Hubble Space Telescope where we proved that both detailed abundance and metallicity analyses are possible for star clusters at distances of several Mpc.

For the first time, horizon scale structure around a supermassive black hole was imaged with the EventHorizonTelescope. In this talk, I will discuss the physical interpretation of the ring-like structure emerging in the center of the galaxy M87. To compare the observations with theoretical expectations, a library of ~60000 theoretical images was obtained from 3D GRMHD simulations with different black hole spins, masses and orientations. The data is consistent with most simulations of a radiatively inefficient accretion flow and yields a black hole mass of 6.5x10^9 Msun, in excellent agreement with the stellar dynamical measurement. Further firm parameter constraints are currently thwarted by the stochastic nature of the underlying models as well as the uncertain modeling of electron physics in near collision-less regimes. More constraints are set by including multi-wavelength data and by using limits on the jet power. I will also briefly discuss implications to alternatives to GR and future prospects for physics with the EHT.

The classical picture of protoplanetary discs forming smooth, continuous structures of gas and dust has been challenged by the growing number of spatially resolved observations. These observations indicate that radial discontinuities and large-scale asymmetries may be common features of the emission of protoplanetary discs, which are often interpreted as signatures of the presence of (unseen) planetary companions. During this seminar, I will report our recent and ongoing efforts to predict the dust’s radio emission in protoplanetary discs due to the presence and orbital evolution of giant planets, through gas+dust hydrodynamical simulations post-processed with dust radiative transfer calculations. I will show via these models that recent ALMA observations strongly suggest the presence of several planets in the discs around MWC 758 and HD 169142.

Recently, X-ray observations revealed that some of evolved supernova remnants (SNRs) have plasmas in which the recombination process becomes more dominant than the ionization process. In most of these SNRs having the recombining plasma (RP), association of molecular and atomic clouds are observed. This implies that the evolution of SNRs are considered to be deeply related to the environment of the ambient gas, though they are not fully understood. In order to study physical and astrophysical causes of the formation of the RP in evolved SNRs, we develop a new framework that provides both X-ray spectra and images of evolved SNRs with an age of > 104 yr. Our model calculates the time evolution of temperatures of electron and ions, which are not considered in previous plasma models, based on a one-dimensional Lagrangian hydrodynamics simulation. We include physical processes of shock heating, energy exchange by Coulomb interaction, radiative cooling and evolution of ionization states. The spectra are composed of bremsstrahlung and emissions by atomic transition of major elements calculated from atomic properties of AtomDB. Since effects of the surrounding environment of SNRs is important in their evolution, we investigate the relation between plasma states in SNRs and interstellar medium (ISM) density using our model by changing ISM density (1, 3, 10, and 30 cm-3). In our simulation, the RP is naturally produced in evolved SNRs (~ 104 yr) which exploded in the dense ISM. We characterize spectra by the electron temperature and ionization temperature that is an indicator of describing the ionization state. As a result of comparing these temperatures of our model with the observations, we successfully demonstrate that the time evolution of ionization and recombination are in excellent agreement with the observed values. Our model holds promising application for future X-ray missions with a high resolution spectrometer.

The PTOLEMY project aims to develop a scalable design for a Cosmic Neutrino Background (CNB) detector, the first of its kind and the only one conceived that can look directly at the image of the Universe encoded in neutrino background produced in the first second after the Big Bang. The scope of the work for the next three years is to complete the conceptual design of this detector and to validate with direct measurements that the non-neutrino backgrounds are below the expected signal from the Big Bang. In this talk I discuss in details the theoretical aspects of the experiment and its physics goals. In particular, I mainly address three issues. First the sensitivity of PTOLEMY to the standard neutrino mass scale. I then consider the perspectives of the experiment to detect the CNB via neutrino capture on tritium as a function of the neutrino mass scale and the energy resolution of the apparatus. Finally, I consider an extra sterile neutrino with mass in the eV range, coupled to the active states via oscillations, which has been advocated in view of neutrino oscillation anomalies. This extra state would contribute to the tritium decay spectrum, and its properties, mass and mixing angle, could be studied by analyzing the features in the beta decay electron spectrum.

From the cosmic-ray spectrum, we know that there must be objects in our galaxy that can accelerate particles to above PeV energies, but it's not clear what they are. Very-High-Energy gamma-rays (E>100 GeV to >100 TeV) provide a useful tool for searching for these accelerators, since they provide a view of non-thermal photon emission from the sites where particles are accelerated. I will present an overview of the problem, how we are using telescopes like HESS (and later CTA) to search for these "PeVatrons" and what difficulties have been encountered. Finally, I will show the latest results, including evidence for an acceleration event in the Galactic Center.

In this talk, I shall review the most peculiar aspects of cosmology in the radio band, with a special focus on the Square Kilometre Array (SKA) radio-telescope and its pathfinders. I shall present the main radio probes that can be exploited for late-time cosmology: continuum and 21-cm line galaxy surveys, neutral hydrogen intensity mapping, and even weak lensing cosmic shear at radio frequencies. Moreover, I shall also discuss the added value of multi- wavelength synergies, presenting some show-case example of the power of radio-optical cross-correlations to test the fundaments of the concordance cosmological model, such as the nature of dark matter and dark energy, or tests of inflation and gravity.

Strong gravitational lenses with measured time delays between the multiple images can be used to determine the Hubble constant that sets the expansion rate of the Universe. Measuring the Hubble constant is crucial for inferring properties of dark energy, spatial curvature of the Universe and neutrino physics. I will describe techniques for measuring the Hubble constant from lensing with a realistic account of systematic uncertainties. A program initiated to measure the Hubble constant to <3.5% in precision from strong lenses is in progress, and I will present the latest results and their implications. Search is underway to find new lenses in imaging surveys. An exciting discovery of the first strongly lensed supernova offered a rare opportunity to perform a true blind test of our modeling techniques. I will show the bright prospects of gravitational lens time delays as an independent and competitive cosmological probe.

The study of the filamentary structures in massive star-forming regions is undergoing a revolution, thanks in large part to the unprecedented high angular resolution and sensitivity that ALMA provides. We have used ALMA to conduct an observational study of two massive filaments and a hub-filament system with the main goal of building a picture of their global dynamical properties and fragmentation. We present the results for the Monoceros R2 (hereafter MonR2) molecular cloud, one of the nearest and clearest examples of a hub-filament system. The central hub hosts a cluster of massive protostars associated with an expanding HII region, where a number of filaments are converging. We have estimated total the mass accretion rate along the filaments on the order of 10^(- 3) Msun/yr. Inside the central hub, the filaments appear twisted forming a spiral-like structure, with signs of rotation and infall motions. Overall, the hub-filament system in MonR2 suggests a scenario of non- isotropic global collapse, forming a massive stellar cluster. We also present our results for G357, which is a massive filament similar to the integral shaped filament (ISF) in Orion A, but shows remarkably low star formation activity. The comparison of the fragmentation and dynamics of G357 and the ISF enables us to address the early evolution of massive filaments.

The cosmic microwave background (CMB) research told us a remarkable story: the structure we see in our Universe such as galaxies, stars, planets, and eventually ourselves originated from tiny quantum fluctuations generated in the early Universe. With the WMAP we have confirmed many of the key predictions of inflation including flatness and statistical homogeneity of our Universe, Gaussianity and adiabaticity of primordial density fluctuations, and a small but non-zero deviation from the scale-invariant spectrum of density fluctuations. Yet, the extraordinary claim requires extraordinary evidence. The last prediction of inflation that is yet to be confirmed is the existence of primordial gravitational waves whose wavelength can be as big as billions of light years. To this end we have proposed to JAXA a new satellite mission called LiteBIRD, whose primary scientific goal is to find signatures of gravitational waves in the polarisation of the CMB. In this presentation we describe the current state of affairs regarding our understanding of the early Universe, physics of polarisation of CMB, and the LiteBIRD mission.

Formulating a Predictive Theory of Galaxy Evolution requires understanding star formation and its dependence on the local environment, spanning the scales from individual stars to kpc–size structures. The physical conditions within galaxies determine the formation of stars, star clusters, and larger structures, and their subsequent evolution. In turn, these structures, through feedback, affect the evolution of the host galaxy. HST observations of external galaxies have enabled the characterization of the young stellar populations with unprecedented accuracy and detail, thus aiding the census and description of those populations. These observations are being used to quantify the spatial distribution and clustering of young stars, and investigate the impact and imprint of the physical conditions of both the local and global environment on the formation and evolution of the multi-scale structures. I will concentrate mainly on the results of the Legacy ExtraGalactic UV Survey (LEGUS), an HST Treasury programs that is investigating these issues using multi-color imaging, from the near-UV to the I, of a sample of nearby galaxies. I will also briefly introduce successor programs that promise to expand our understanding of star formation and feedback on galactic scales.

The discovery and characterization of extrasolar planets has been data-driven:  clearly there are more things in heaven and earth than are dreamt of in our philosophies.  As the demographics of the myriad diverse systems becomes known, we begin to piece together the larger story of their formation and evolution. Ultimately, we seek to understand the prospects for life elsewhere in the Universe. In addition to this scientific quest, ‘exploration’ also plays a role. In particular, the nearest star systems provide an opportunity to explore in detail strange new worlds. The announcement of a planet < 10 Mearth in the liquid-water zone of Proxima Centari sent shock waves through the community. What is the nature of this planetary system found in our own galactic backyard? Could it be habitable? Here we will review plans to try to image small planets from the ground in thermal emission around the nearest stars, including development of a new generation of mid-infrared detectors with high quantum efficiency, low noise, and suitable for ground-based use, as well as instruments planned for the next generation extremely large telescopes such as METIS on the E-ELT. We will also discuss the power of imaging planets both in reflected light and thermal emission, and the possibility of detecting the greenhouse effect in a world outside the Solar System.

The birth of a neutron star with an extremely strong magnetic field, called a magnetar, has emerged as a promising scenario to power a variety of outstanding explosive events. This includes gamma-ray bursts, supernovae with extreme kinetic energies called hypernovae and super-luminous supernovae. The origin of these extreme magnetic fields (of the order of 10^15 Gauss) is not fully understood yet and requires an amplification over several orders of magnitude during the formation of the neutron star. I will describe our current understanding of the physical processes that may lead to this magnetic field amplification and the consequences for the explosion properties.

Recent observations have emphasized the importance of the formation and evolution of magnetized filamentary molecular clouds in the process of star formation. Theoretical and observational investigations have provided convincing evidence for the formation of molecular cloud cores by the gravitational fragmentation of filamentary molecular clouds. Thus, the mass function and rotations of molecular cloud cores should be directly related to the properties of the filamentary molecular cloud, which determines the initial size and mass distribution of a protoplanetary disk around a protostar created in a core. In this talk I explain our current understanding of the star formation processes in the Galactic disk, and summarize various processes that are required in describing the filamentary molecular clouds to understand the star formation rate/efficiency, the stellar initial mass function, and the angular momentum distribution of protoplanetary disks in their early evolutionary phase.

Star formation is one of the main drivers of galaxy evolution, but an understanding of this process remains elusive. This is caused by a lack of systematic observational constraints on cloud scales. Star formation in galaxies is expected to be highly dependent on the galactic structure and environment, as it results from a competition between mechanisms such as gravitational collapse, shear, spiral arm passages, cloud-cloud collisions, and feedback. A statistically representative sample of galaxies is therefore needed to probe the wide range of conditions under which stars form. I will present the first systematic characterisation of the evolutionary timeline of molecular clouds and star-forming regions, derived by applying the statistical method of Kruijssen & Longmore (2014) and Kruijssen et al. (2018) to homogeneous ALMA + optical observations at 50 pc resolution of a large sample of star- forming disc galaxies out to 17 Mpc (obtained in the context of the PHANGS collaboration). This method uses the multi-scale nature of the star formation relation to constrain the timeline and efficiencies for star formation and feedback on the cloud scale, across a wide variety of galactic environments. I will show that star formation is regulated by efficient stellar feedback, driving GMC dispersal on short timescales (1-5 Myr) due to radiation and stellar winds, prior to supernova explosions. This feedback limits GMC lifetimes to about one dynamical timescale (10-30 Myr), with integrated star formation efficiencies of only a few percent. Our findings reveal that galaxies consist of building blocks undergoing vigorous, feedback-driven lifecycles, that vary with the galactic environment and collectively define how galaxies form stars. These observations settle a long-standing question on the multi-scale lifecycle of gas and stars in galaxies, and open up the exciting prospect of studying cloud-scale star formation and feedback in galaxies across cosmic time.

MAXI (Monitor of All-sky X-ray Imager) was launched in 2009 and installed on the International Space Station.It consists of the Gas Slit Camera (GSC) and the Solid-State Camera. The GSC, gas proportional counter array, covers the energy range from 2.0kev to 30keV while the SSC, CCD cameras, covers the energy range from 0.7keV to 7keV. In the seminar, I will focus on the SSC. The SSC consists of 32 CCDs in total with a mechanical slit. The CCD performance is gradually degrading in orbit due to its harsh radiation environment. I will report on the diffuse X-ray background maps obtained in energies of 0.7--1.0, 1.0--2.0, and 2.0--4.0 keV, respectively. They are the first ones that were derived with a solid-state instrument. The diffuse soft X-ray background was discovered in the past by using sounding rocket experiments and studied in detail by ROSAT All Sky Survey (RASS). After that, we learnt that the solar wind charge exchange (SWCX) was a nuisance in X-ray astronomy, particularly below 1.0keV. The SWCX is believed to depend on the solar activity and seriously affects the diffuse X-ray background. RASS was done in high solar activity while SSC was done in low solar activity separating about 20 years. Our result shows a good correlation with that by RASS.

Star formation is a complex process that involves dusty gaseous structures covering orders of magnitude in spatial scales and gas densities. How the physical properties and dynamical evolution of these structures relate to a particular star formation event is yet to be fully uncovered. In the past decade, some progress has been made on linking the properties of low-mass star-forming cores to those of the interstellar filaments in which they most often form. On the other hand, there is also a growing body of evidence suggesting that the reservoirs from which massive (proto)stars accrete gas from are typically much larger than those for low-mass protostars. Trying to determine what physical process fixes the properties of these mass reservoirs, and finding out how they evolve towards the formation of individual stars and stellar clusters is at the heart of current star formation research. In this context, I will present recent observational studies aiming at understanding how gas flows from the scale of a giant molecular cloud to individual massive-star forming cores, and how feedback from recently formed OB stars affect their parent molecular cloud. I will discuss how the corresponding findings impact our current knowledge on molecular cloud structure and dynamical evolution of dense star-forming clumps.

The Universe is infinitely large and dramatically dark, apparently dominated by unknown components which make up most of the matter/energy budget. Fortunately, that tiny 4.6% of baryons act under the robust laws of nuclear physics and stellar evolution, theories which we can use to understand the bright side of the Universe. In this talk I shall discuss interpretative models for distant galaxies and illustrate the historical path that paved the way to modern calculations. I shall then use those models to infer conclusions on the formation and evolution of the most massive galaxies.

Distant galaxy clusters are powerful laboratories for observing the hierarchical growth of large-scale structure, constraining cosmological parameters, and for studying the formation of galaxies. However, distant (z>1.5) clusters are extremely rare and faint, so locating and studying them poses a significant observational challenge. In this seminar, I will review the theory of cluster formation and present recent advances we have made in detecting and studying distant galaxy clusters.

The top recommendation for a large space mission in the US 2010 Decadal Survey was the Wide Field Infrared Survey Telescope (WFIRST). Similarities in hardware requirements between proposed dark energy, exoplanet microlensing, and near infrared surveyor missions allowed for a single mission that would accomplish all three goals. The gift of an existing 2.4 meter telescope to NASA by another US government agency allowed for the addition of a coronagraph that will take images and spectra of nearby exoplanets; this instrument will be a technological stepping stone to imaging other Earths in the 2030s. I will give an overview of WFIRST's proposed instrumentation, science goals, and implementation plan.

Star forming dwarf galaxies are by far the most abundant type of galaxies in the local Universe. They also lie at the base of the hierarchical structure formation ladder - as they later merge into larger halos. Understanding the baryon cycle in these galaxies is critical towards solving the major mismatches between observations and simulations of structure formation. Empirically constraining the relationship between gas and star formation in these galaxies remains challenging though, given their faintness across all observed wavelengths. I will describe our efforts to empirically quantify the relation between gas and star formation using the 21 cm emission line from atomic hydrogen (HI) as a tracer of gas, not only in dwarfs but also in the HI-dominated outskirts of spirals.

eROSITA (extended ROentgen Survey with an Imaging Telescope Array) is the core instrument on the Russian/German Spektrum-Roentgen-Gamma (SRG) mission which is current scheduled for launch in 2018. In the soft band (0.5-2 keV), the deep All-sky survey will be 30 times more sensitive than the previous ROSAT All-sky survey, while the first ever true all-sky survey will be mapped in the hard band (2-8 keV). The design driving science is the detection of large samples of galaxy clusters to redshifts z > 1, in order to study the large scale structure in the Universe and test cosmological models including Dark Energy. In addition, eROSITA is expected to yield a sample of around 3 million active galactic nuclei, which is bound to revolutionize our view of the evolution of supermassive black holes and their impact on the process of structure formation in the Universe. Finally, the survey will also provide new insights into a wide range of astrophysical phenomena, including neutron stars and pulsars, X-ray binaries, active stars and diffuse emission from supernova remnants. The talk reports on the status of eROSITA and its scientific prospects. In the end, I will also briefly discuss how the German eROSITA consortium is activated for ensuring an adequate follow-up of the sources to be discovered.

The ability to obtain high quality data in a short amount of time or indeed to recover high resolution images from from incomplete blurred and noisy data can significantly improve the results of experiments potentially leading to new and exciting scientific discoveries. Mathematical techniques such as compressed sensing and sparse regularisation provide these benefits for many sources of data in a variety of different fields. Compressed Sensing for Magnetic Resonance Imaging and Cosmology (COSMIC) is a CEA DRF funded project that brings together MRI experts at NeuroSpin with astronomical image analysis experts at CosmoStat in order to develop an open source software package called PySAP (Python Sparse data Analysis Package) that implements these signal processing tools. This talk will provide a brief introduction to the types of problems encountered in acquiring/processing MRI and astrophysical images and demonstrate how the tools provided in PySAP can be beneficial.

The formation of stars is a fundamental aspect of how matter evolves in the Universe. It dictates timescales, chemical and structure evolution of baryons. It is the respiration of galaxies; star formation makes galaxies “boil”, bubble and fragment. Without it the Universe would have ended up in a sterile collection of gravitational singularities. Star formation creates structures as a result of specific non-linear physical processes. In that respect, a galaxy is a complex, self-organized system. This complexity is revealed by the multi-scale and multi-phase nature of the interstellar medium. This talk will be about the use of multi-wavelength, and especially hyper-spectral data, to uncover aspects of the energy and matter cascade of the interstellar medium of the Milky Way. I will present how such data (dust, CO, 21 cm) and their comparison to numerical simulations, can be used to get a clearer view of the evolution of diffuse matter in a galaxy like the Milky Way. In particular I will present recent results on the use of dust scattering to trace the cascade of the ISM cascade down to very small scales, as well as our current work on the analysis of large 21 cm datasets to uncover the first steps of the formation of cold and dense structures in the diffuse ISM.

Over the past 45 years, investigations of ultraviolet absorption features in stellar spectra have revealed that most of the heavy elements in the interstellar medium are depleted from the gas phase to values well below solar or B star reference abundances. The strengths of such depletions reveal the composition of dust grains in space, and they can be characterized by a limited set of parameters that are closely linked to the average gas densities and the condensation temperatures of the elements. Two outstanding mysteries remain: one is the fact that the depletion of oxygen exceeds that needed for forming silicates or metallic oxides, and the other is that the chemically inert element krypton shows some depletion. When we observe absorption features to derive the element abundances in distant galaxies, we must understand how to correct for depletions by using the patterns found in our Galaxy or the Small Magellanic Cloud as examples. Comparisons of interstellar abundances to those found in circumstellar disks may help us to understand better the replenishment and dispersal of gaseous matter in such systems.

In this presentation I will talk mainly about Cassini discoveries and results concerning the outer edge of Saturn’s main rings, that is a very peculiar place called the «Roche limit». In this region, accretion processes are balanced by tidal forces producing a variety of time variable structures because of the endless competition of these two processes. Temporary moons, ringlets regularly destroyed by moonless interactions, a complex interplay have been discovered. I will talk about mainly about of strange physics of this region and show that moons and rings are the two sides of a same system. Many discovered processes are similar to still unobserved mechanisms invoked for planetary formation. The discussion will also extend to the formation of short-period planets around white dwarves, that can be explained by exactly the same processes.

The Multi-Unit Spectroscopic Explorer (MUSE) is an integral field spectrograph with unique capabilities on the Very Large Telescope. With its high sensitivity and by providing a complete view of the optical spectrum over 1 arcmin2 it has been a tremendous breakthrough in the way galactic and extragalactic observations are performed. The success of MUSE calls for new ideas for the next generation of IFUs, and I will present the concept of a BlueMUSE. With a field of view increased up to 1.4 x 1.4 arcmin2 and a higher spectral resolution, BlueMUSE is covering wavelengths down to the atmospheric cut-off (350 nm). The current instrumental concept currently being investigated includes the use of curved detectors. BlueMUSE opens up a new range of galactic and extragalactic science cases allowed by its specific capabilities: including for example the study of young stars, the properties of the gas in the circumgalactic medium, and high redshift clusters.

Wojtak, Hansen and Hjorth and others have measured the long-predicted gravitational redshift of light escaping from galaxy clusters. The effect is very small, corresponding to a velocity shift of only about 10 km/s, but the result appears to be fairly robust and seemed to be in good agreement with general relativity predictions and possibly in conflict with some alternative theories. The effect was initially imagined to be a simple astronomical analogue of the famous terrestrial Pound and Rebka experiment that verified Einstein's theoretical prediction. However, it was soon realised that the physics of this effect is considerably more complex. As I shall describe, there are actually three other contributions to the measured signal that need to be taken into account. I shall describe recent attempts to model these effects using N-body experiments, and how this effect may be useful for testing alternative theories of gravity. Understanding this apparently simple effect reveals some subtleties in special relativity and also sheds light on the interpretation of redshifts in cosmology.

The gas mass and star formation rate of damped Lyman-alpha absorbers (DLAs), a population of high-redshift absorption-selected galaxies, have been open questions in the field of galaxy evolution for more than three decades. This talk will describe new results from ALMA searches for CO and CII-158 micron emission from a sample of DLAs over a wide range of redshifts, z~0.5-4.2. These are the first CO and CII-158 micron detections in DLA host galaxies, providing a new window on physical conditions in absorption-selected galaxies, and yielding a new tool to identify DLA host galaxies at high redshifts.

In the local universe, a star has a higher probability of being in a galaxy of the mass of the Milky Way than in any other galaxy, and we have the opportunity to be able to study one such galaxy from the inside. We can, in particular, study its stellar mass growth with time, and understand how each of the known stellar populations is connected to this mass growth history. While much is expected from the analysis of the Gaia data in this regard, it is safe to say that a change of paradigm concerning the stellar populations of our Galaxy is already under way, due in particular to important results coming from the analysis of recent spectroscopic surveys. I will present and discuss some of these results.

PILOT is an experiment with a stratospheric balloon designed to measure the thermal dust polarized emission at 240 microns which enables to measure the geometry of the magnetic field in the Interstellar Medium using multiplexed bolometric detectors developed by CEA for the Herschel PACS mission. In this talk, we will describe the instrument and its performances measured during the first two flights that took place in 2015 and 2017 from Canada and form Australia respectively. We will discuss the first scientific results on the geometry of the magnetic field in the central molecular zone of our Galaxy. We will insist on the strict control of systematic instrumental effects crucial for this type of measurements and the associated difficulties in the data treatment and calibrations. Finally, we will talk of the future PILOT project and in particular its evolution to COPILOT designed to measure the integrated emission of the C+ line in the ISM and to become a demonstrator of the detection chain for the SPICA-POL instrument.

With recent advances in numerical techniques and computing power theoretical modeling of a core-collapse supernova (CCSN), a cataclysmic event marking the end of the lifetime of a massive star, has become feasible in three spatial dimensions. In this talk, I will review recent progress which have been made in modeling the long-term evolution of CCSN explosion starting from the collapse and explosion phase until the SN ejecta transform into the early SN remnant phase. I will discuss how simulation results can be compared with observables such as explosion asymmetries, element distributions, SN light curves, and pulsar kick velocities that are obtained from recent observations of SN and SN remnants.

We will present the science goals of the SVOM mission and how the Microchannel X-ray Telescope (MXT) will contribute to reach them. SVOM a a Sino-French mission (to be launched by the end of 2021) dedicated to Gamma-Ray Bursts and transient sky studies, and MXT is part of the payload that will be delivered by France. It is a focussing soft X-ray (0,3-6 keV) telescope, which is based on a new optical concept called "Lobster-Eye", coupled to a low noise pn CCD detector. The Irfu/DAp carries the scientific responsibility of the entire telescope, and is in charge of the development of the camera, including all the functions around the detector to get optimal performance. We will present the design of the camera, the associated challenges and the recent achievements.

The Sloan Digital Sky Survey (SDSS) has been mapping the sky for almost a decade, providing crucial information on the dark universe though measurements of BAO and RSD (redshift space distortions). As one of the SDSS components, the Lyman-alpha forest survey is a rich source of information. Because it gives access to small (tens of Mpc) scales, it allows one to probe the impact on the clustering of matter of neutrino mass and warm dark matter. I will briefly recall the major goals of SDSS, and introduce the quasar survey where the Lyman-alpha forest is measured. I will then present one of the strongest constraints on neutrino mass from a combination of CMB and Lyman-alpha data. Finally, I will show how the study of clustering in the Lyman-alpha forest can also lead to competitive constraints on warm dark matter and on several models of keV sterile neutrinos.

In 2015, at COP21, governments invited the IPCC to prepare this special report. It was approved by delegates from all governments in October 2018, on the basis of the assessment performed by 91 authors from 40 countries, with 133 contributors, of 6000 publications, after 3 rounds of review (1131 reviewers, more than 42 000 review comments). This report provides the current state of global warming, with 1°C due to human activities; the consequences of an additional half a degree or one degree of global warming; the greenhouse gas emission trajectories consistent with stabilisations at 1.5°C or 2°C; the systems transitions, with an assessment of 6 dimensions of feasibility; the multiple intersections with sustainable development goals. This report is so stimulating that governements could not find words to receive it. In December 2018, at COP24, four of them (Saudi Arabia, Kuweit, USA and Russia) refused to welcome it. The COP24 decision expresses its appreciation for the work done, welcomes the timely completion of the report, and invites parties to make use of it...

Over the last few years, enormous progress has been made probing galaxies in the first two billion years thanks to the incredible capabilities of the Hubble and Spitzer Space Telescopes. Already, more than 1500 probable galaxies are known at redshifts above z~6, and now the current frontier is at z~9-10, with 50 plausible galaxy identifications to date, and a credible spectroscopic redshift determination to z=11.1. Deriving physical properties for these distant galaxies is also an important frontier, and progress has been impressive even as early as z~7-8, with probes of nebular emission-line strengths and specific star formation rates to z~8.5 and new constraints on dust-enshrouded star formation at z>~2 from ALMA. One exciting emerging frontier has been probes of ultra-faint galaxies in the early universe with the Hubble Frontier Fields (HFF) program using gravitational lensing and long exposures. To guarantee the best results, accurate determinations of both the size distribution and lensing models are required. In this colloquium, I describe new work on the HFFs, while surveying many current highlights on early galaxy research.

Exoplanet detection surveys over the last twenty years have revealed a surprising diversity of planets orbiting other stars— this revolution is fuelled by fundamental questions about the place of the Earth and the Solar System in the Universe. How do planets form? What range in architectures of planetary systems exist? How does our Solar System fit into this context? And perhaps the most exciting of all: do other life-bearing planets exist? The study of exoplanet atmospheres is the next step in leveraging exoplanetary detections. This is because a planet’s atmosphere provides a fossil record of its primordial origins and controls its fate, size, appearance, and ultimately its habitability. In this context, I present comparative exoplanetology programs that aim at characterising planetary systems transiting nearby stars through the observations of their atmospheres. Our findings on the atmospheric composition and physical properties provide insights into the formation and evolution of planetary systems and enhance our understanding of our own Solar System’s formation. Finally, I also present strategies for probing habitable exoplanet atmospheres in the quest for bio-signatures.

Over a large range of equilibrium temperatures clouds seem to dominate the transmission spectrum of exoplanets atmospheres, but no trends allowing the classification of these objects have yet emerged. Recently, Kepler observations of the light reflected by hot Jupiters show that an inhomogeneous, asymmetric and time-dependent cloud coverage is present in these planets. Interestingly, this asymmetry depends on the equilibrium temperature of the planet. Using state-of-the-art three dimensional models of hot Jupiters atmospheres, I will show that longitudinal and latitudinal asymmetry in the cloud coverage is expected for these hot planets. The presence of such an inhomogeneous cloud coverage can bias the retrieved abundances from transmission and secondary eclipse spectra and even lead to erroneous molecular detections. Thermal phase curves are also affected, and our understanding of heat transport by the atmosphere cannot be complete without taking clouds into account. The longitudinal cloud asymmetry being a strong function of the condensation temperature of the cloud species, it is a telltale of the cloud composition. Observations and models converge towards a similar conclusion: an L/T-like transition is expected for hot Jupiters, with silicate clouds disappearing from the cooler planets and being replaced by manganese sulfide clouds.

Gamma-ray bursts are the most luminous electromagnetic events in the universe. They fall into two, broad categories: long-duration (more than 2 s) bursts, which are powered by the core collapse of rapidly rotating massive stars, and short-duration (less than 2 s) bursts, for which binary neutron star and neutron star-black hole mergers are the leading progenitor candidates. In both scenarios, gravitational waves are expected to accompany the gamma-ray burst, making these transient phenomena promising events for gravitational-wave follow-up. In this talk, I review the status of targeted searches for gravitational waves in association with gamma-ray bursts and discuss the prospects of joint electromagnetic and gravitation-wave observations. I also present the results of these searches obtained during the first Advanced LIGO observing run, which was carried out between September 2015 and January 2016.

With the novel world-leading radio telescope LOFAR (the Low Frequency Array), astronomers are expected to detect the cosmological radiation emitted billions of years ago, from the time of the first ‘stars’. However, detection of this weak emission is difficult. Synchrotron emission from our own Galaxy intervenes, like mist on an autumn morning. To clear the view towards the early childhood of the Universe, we need to study the emission from our Galaxy in great detail. During my talk I will give an overview of the LOFAR-EoR key science project, its challenges and present its most recent results. A special focus will be given to the rich morphological features discovered with the LOFAR in several fields at high Galactic latitudes, associated with small column densities of the interstellar medium located somewhere within the Local Bubble. At the end I will discuss their puzzling correlation with the Planck dust polarisation data and HI data.

Polarized emission from cold Galactic dust is the most important and troublesome foreground for searches of an inflation-probing B-mode signal in the polarization of the cosmic microwave background (CMB). To get to the primordial B-modes, we need to subtract polarized emission of magnetized interstellar dust with high accuracy. A critical piece of this puzzle is the 3-d structure of the magnetic field threading dust clouds, which cannot be accessed through microwave observations alone. However, observations of a large number of stars at known distances in optical polarization, tracing the same CMB-obscuring dust, can map the magnetic field between them. The Polar Area Stellar Imaging in Polarization High Accuracy Experiment (PASIPHAE) will deliver such a map combining novel-technology wide-field-optimized optical polarimeters and an extraordinary commitment of observing time by the Skinakas observatory in Crete and the South African Astronomical Observatory. We will cover >9000 square degrees in the areas of the sky targeted by CMB experiments, measuring linear optical polarization at 0.2% accuracy of over 360 stars per square degree, a 1000-fold increase over the state of the art. Such a map would not only boost CMB polarization foreground removal, but it would also have a profound impact in a wide range of astrophysical research, including interstellar medium physics, high-energy astrophysics, and galactic evolution.

The field of gravitational microlensing is booming, in particular due to the success of several space-based missions. I will review recent discoveries and developments in exoplanet search through gravitational microlensing, with a special focus on statistics of exoplanets, brown dwarfs and free-floating planets, and the Spitzer and Kepler/K2 follow-up of microlensing events using space-based parallax. I will outline the prospects of future techniques and instruments, such as the observations of microlensing events through interferometry and the promise of the WFIRST mission for microlensing.

Observations reveal that star formation is progressively quenched in more massive galaxies and in denser environments. What are the main physical mechanisms able to moderate and stop star formation? An obvious one is the energetic feedback from AGN, where recently massive molecular outflows have been observed. Observational evidence will be shown with ALMA and NOEMA results. The mass outflow rate is estimated between 1-5 times the star formation rate. When driven by AGN, these outflows are therefore a clear way to moderate or suppress star formation. However, AGN feedback can be also positive, and evidence will be presented. Group and cluster environment can perturb considerably galaxies, quench their star formation, and transform their morphology in very short time-scales. I will present evidence of gas removal, where not only the external atomic gas is involved, but also inner molecular gas. Star formation still occurs in the tails, however with a much lower efficiency. The survival of dense clouds in harsh environments will be discussed.

In a first part of the seminar I shall discuss how from the observed surface abundances of extremely iron-poor stars, it is possible to deduce interesting properties of the first massive star generations in the Universe. These very iron-poor low mass (and therefore long-lived) stars are made of material made of a mixture of interstellar medium and of ejecta by a few, may be only one star. The very low iron content implies that not many generations of stars could enrich the pocket from which these iron-poor stars formed and thus favor short lifetimes stars as massive ones. The massive star(s) responsible for the main abundance properties of these very iron-poor stars are called the source star(s). First, based on nucleosynthetic arguments, we will deduce that necessarily some mixing processes occurred in the source stars and that only its outer layers have been ejected. Second we shall show how rotation might provide both the driving for the mixing and for the envelope ejection. Third, we shall discuss other consequences of these models for the production of nitrogen, carbon isotopes and s-process elements in the early Universe. In a second part, if time permits, we would like to discuss the origin of some short lived radionuclides that were present, still non-decayed, in the cloud that gave birth to the solar system and were incorporated in some meteorites. We will see that the analysis of tiny amounts of meteoritic material can provide wonderful constraints on the near stellar environment of the solar system 4.56 Gyr ago. In that context we shall discuss the importance of mass loss by stellar winds that seems to be a key ingredient to explain the observed amounts of 26Al and 60Fe.

Structure formation is very sensitive to the primordial conditions and dynamical properties of the Universe. In fact, it is a promising probe of dark energy, dark matter properties, primordial non-gaussianity or neutrino masses. A major difficulty to harvest these results is that a significant fraction of the information lies at non-linear scales. It is thus essential (in particular to extract new physics) to develop efficient tools to study large scale structure beyond linear theory. In this talk I will describe the methods based on perturbation theory of a fluid-like medium, emphasising the new developments. The latter are particularly relevant to understand the evolution of the BAO and to parameterise the influence of small scales on mildly non-linear scales

The interstellar medium (ISM) of galaxies drives galaxy evolution. However, its multi-phase structure is typically unresolved in cosmological galaxy formation simulations. I present recent progress on high-resolution numerical simulations (the SILCC project) investigating the differential impact of major physical processes setting the chemical and thermal multi-phase structure of the ISM including OB stellar winds, radiation and supernova explosions. We find evidence that stellar winds and radiation from massive stars primarily regulate star formation, while supernova explosions set the properties of the outflow driving hot gas. I also discuss the potential impact of non-thermal ISM components - magnetic fields and cosmic rays - on galactic outflows. With these simulations we also make first attempts towards more accurate predictions of important emission lines which are a major observables for galaxy formations studies at all cosmic epochs.

Supernova remnants 101: The large amount of energy released in the supernova explosion leads to the creation of a fast shock wave which is an important source of kinetic and thermal energy in the interstellar medium. This shock wave is also believed to accelerate the bulk of Galactic cosmic rays. As I believe that there has not been a general Supernova remnant (SNR) seminar in a long time, I will take this opportunity to make a short and biased introduction to SNRs, present the current scientific questions, and what we’ve learned from high-energy observations in the recent years. In particular, I will focus on our recent work on the source RX J1713.7−3946, an excellent target to investigate particle acceleration in SNRs since it is one of the brightest sources of the TeV sky and exhibits strong synchrotron emission in X-rays. I will conclude by discussing SNRs from a population point of view in gamma-rays with the Fermi-LAT SNR catalog in the context of time dependent evolution models.

Stars originate by the gravitational collapse of a turbulent molecular cloud of a diffuse medium, and are often observed to form clusters. Stellar clusters therefore play an important role in our understanding of star formation and of the dynamical processes at play. However, investigating the star formation is difficult because its physics is complex to be properly modeled, and because star forming regions are obscured by dust, which severely limits observations to infrared and radio bands only. As a consequence hierarchical-step approaches to decompose the problem into different stages are required, as well as reliable assumptions on the initial conditions in the clouds. In this seminar I will report for the first time on the use of asteroseismology, namely the study of stellar oscillations, to put strong constraints on the early formation stages of open clusters, up to more than 8 billion years old. I will introduce you to asteroseismology, and then describe the analysis performed on a sample of 50 red giant stars in the old open clusters NGC 6791 and NGC 6819 observed by NASA Kepler, for which nearly 4000 oscillation modes have been fully characterized. I will therefore present the important discovery made about the rotation history of these clusters and how 3D hydrodynamical simulations for stellar cluster formation can be used to constrain the physical processes of turbulence and rotation that are in action during the proto-cluster formation. The results and implications of this work will be relevant for different fields in astrophysics, including planetary formation and galaxy formation, structure, and evolution.

In this talk I will focus on three aspects of interstellar dust that have a direct bearing on its chemistry and its effects on interstellar chemistry. These are:
- the nano-particle-driven catalytic formation of the key interstellar species H2 and OH,
- the relationship between dust and the diffuse interstellar bands (DIBs) and
- the nature and evolution of core/mantle grains in the interstellar medium.
I will introduce these three topics and discuss what I would consider to be the fundamental links between them within the framework the recent interstellar dust model THEMIS (The Heterogeneous dust Evolution Model for Interstellar Solids; Jones et al. 2013, Köhler et al. 2014, 2015). In essence, it is my view that we can no longer think of dust as only providing a passive surface for the hit-stick-react-unstick formation of radicals and simple molecules such as molecular hydrogen. Instead we should consider the dust itself as a chemically-active source. As proposed within the THEMIS framework, dust is likely undergoing continuous evolution as it responds to its local environment, with the nature of the outer mantle layers playing a key role in that evolution (e.g., Jones et al. 2016, Ysard et al. 2016). This talk takes these ideas further and explores the consequences of an active evolution of dust within the ISM and its effects on the chemistry of the ISM. All of the ideas presented within this talk are published in a series of paper in Royal Society Open Science (Jones 2016a,b,c).

Low-mass galaxies are the most numerous type of extragalactic system at all epochs of the universe. The population of low-mass galaxies in the local volume allows unique astrophysical and cosmological perspectives that are unavailable in more distant or more massive systems. The ALFALFA blind extragalactic HI survey has cataloged tens of thousands of gas-rich galaxies in the local universe and has populated the faint end of the HI mass function with statistical confidence for the first time. In this talk I will present results from comprehensive follow-up observing campaigns designed to study the low-redshift, low-mass, gas-rich population discovered by ALFALFA. The centerpiece of this effort is the Survey of HI in Extremely Low-mass Dwarfs (SHIELD), an ongoing multi-wavelength investigation of the properties of 82 extremely low-mass galaxies selected from the complete ALFALFA catalog. I will also discuss results from parallel ongoing observing programs that explore more exotic low-mass objects, including "ultra compact high velocity clouds" (HI clouds with structural parameters that match those of gas-bearing "mini-halos" if located within ~1 Mpc), candidate "dark galaxies" (systems with extreme hydrogen mass to stellar light ratios), and targeted studies of individual sources of interest (including two of the most metal-poor galaxies known in the universe). Taken as a whole, these observing programs are furthering our understanding of the continuum of galaxy properties in the low-mass regime.

Massive black holes, weighing millions to billions of solar masses, inhabit the centers of today's galaxies. Black hole masses typically scale with properties of their hosts, such as bulge mass and velocity dispersion. The progenitors of these black holes powered luminous quasars within the first billion years of the Universe. The first massive black holes must therefore have formed around the time the first stars and galaxies appeared, and then evolved along with their hosts for the past thirteen billion years. I will discuss some aspects of the cosmic evolution of massive black holes, from their formation to their growth and how different physical processes shape the relation between black holes and galaxies.

I will present cosmology constraints from a combined analysis of galaxy clustering and weak gravitational lensing, using 1321 deg^2 of griz imaging data from the first year of the Dark Energy Survey (DES Y1). The analysis combines (i) the cosmic shear correlation function of 26 million source galaxies in four redshift bins, (ii) the galaxy angular autocorrelation function of 650,000 luminous red galaxies in five redshift bins, and (iii) the galaxy-shear cross-correlation of luminous red galaxy positions and source galaxy shears. These three measurements yield consistent cosmological results, and provide constraints on the amplitude of density fluctuations (S_8 = 0.794+0.029-0.027) and dark energy equation of state (w = -0.80+0.20-0.22) that are competitive and compatible with those from Planck cosmic microwave background measurements. I will also provide an outlook on upcoming weak lensing results from DES on clusters of galaxies and density tomography, a newly developed higher-order statistic.

The evolution of protoplanetary disks is regulated by the interplay of various physical processes related to the interaction between the star and the disk, such as accretion of material onto the star and emission of material through winds. These processes are best studied spectroscopically. Instruments like the VLT/X-Shooter spectrograph allow us to observe simultaneously the signatures of the accretion process, such as the UV-excess and the emission lines, together with lines tracing winds and outflows, such as helium lines and forbidden lines. At the same time, such spectra allow us to robustly derive the physical parameters of the central objects, such as their temperature and their mass.
When this information is combined with observations of disks at sub-mm wavelengths with ALMA it is then possible to quantitatively constrain disk evolution mechanisms.
I will report on the dependence of the mass accretion rate with stellar mass and disk mass for the complete samples of low-mass objects in the Lupus and Chamaeleon star-forming regions, and discuss the theoretical framework we are working on to explain these observations.
I will also present how we are using Gaia data to study young clusters, and how we are preparing to use future Gaia DR2 data to understand the effect of interactions between stars in the cluster on the evolution of disks.

Radio astronomy is entering a new golden age with the emergence of continental-scale ground-based interferometers such as LOFAR, MeerKAT and SKA. They provide a large field of view as well as high angular ("), spectral (Hz) and temporal resolutions (microsecond) at huge sensitivity over a large frequency spectrum (from about 50 MHz to 10s of GHz). At the same time, the recent mathematical framework of "Compressed Sensing" led to new signal processing algorithmic developments that can be used for robust and sparse signal reconstructions. After introducing these two topics, I will present some developments done at their interface that are led by the team Cosmostat and LEPCHE in collaboration with SKA South Africa. Using the general « compressed sensing » framework combined with sparse representations and convex optimization, we developed two important applications for image reconstruction from interferometric data. First, the improved performance of new instruments can be better exploited to study "slow" (more than 1min) and "fast" (less than 1min) radio transients in the image plane. Unlike frame-by-frame detection, we extended the sparse reconstruction to the third dimension by constraining the reconstruction in time, therefore increasing the detection and characterization of the transient sources. Second, LOFAR and SKA are essentially spectrometers which provide measurements in a very large number of frequency channels. Each channel contains a mix of contributions from various astrophysical sources in the field of view. Based on a sparse source separations method, it is possible to disentangle both spatially and spectrally the various contributions for proper spectral imaging. I will then discuss why more developments are required in this field to improve the scientific return of SKA-class instruments with the advanced calibration of the deluge of data generated by these instruments.

Birmingham University