3 sujets IRFU/DPhP

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• Astrophysics

 

Detecting the first clusters of galaxies in the Universe in the maps of the cosmic microwave background

SL-DRF-24-0595

Research field : Astrophysics
Location :

Service de Physique des Particules (DPHP)

Groupe Cosmologie Millimétique

Saclay

Contact :

Jean-Baptiste Melin

Starting date : 01-09-2024

Contact :

Jean-Baptiste Melin
CEA - DRF/IRFU/DPHP/Cosmo mm

01 69 08 73 80

Thesis supervisor :

Jean-Baptiste Melin
CEA - DRF/IRFU/DPHP/Cosmo mm

01 69 08 73 80

Laboratory link : https://irfu.cea.fr

Galaxy clusters, located at the node of the cosmic web, are the largest gravitationally bound structures in the Universe. Their abundance and spatial distribution are very sensitive to cosmological parameters, such the matter density in the Universe. Galaxy clusters thus constitute a powerful cosmological probe. They have proven to be an efficient probe in the last years (Planck, South Pole Telescope, XXL, etc.) and they are expected to make great progress in the coming years (Euclid, Vera Rubin Observatory, Simons Observatory, CMB- S4, etc.).
The cosmological power of galaxy clusters increases with the size of the redshift range covered by the catalogue. The attached figure shows the redshift ranges covered by the catalogues of galaxy clusters extracted from experiments observing the cosmic microwave background (first light emitted in the Universe 380,000 years after the Big Bag). One can see that Planck detected the most massive clusters in the Universe in the redshift range 0 Only the experiments studying the cosmic microwave background will be able to observe the hot gas in these first clusters at 2 One thus needs to understand and model the emission of the gas as a function of redshift, but also the emission of radio and infrared galaxies inside the clusters to be ready to detect the first clusters in the Universe. Irfu/DPhP developed the first tools for detecting clusters of galaxies in cosmic microwave background data in the 2000s. These tools have been used successfully on Planck data and on ground-based data, such as the data from the SPT experiment. They are efficient at detecting clusters of galaxies whose emission is dominated by the gas, but their performance is unknown when the emission from radio and infrared galaxies is significant.
This thesis will first study and model the radio and infrared emission from galaxies in the clusters detected in the cosmic microwave background data (Planck, SPT and ACT) as a function of redshift.
Secondly, one will quantify the impact of these emissions on existing cluster detection tools, in the redshift range currently being probed (0 Finally, based on our knowledge of these radio and infrared emissions from galaxies in clusters, we will develop a new cluster extraction tool for high redshift clusters (2
Data analysis and fundamental physics with LISA and Pulsar Timing Array

SL-DRF-24-0288

Research field : Astrophysics
Location :

Service de Physique des Particules (DPHP)

Groupe Astroparticules (GAP)

Saclay

Contact :

Marc Besancon

Antoine PETITEAU

Starting date : 01-10-2024

Contact :

Marc Besancon
CEA - DSM/IRFU/SPP


Thesis supervisor :

Antoine PETITEAU
CEA - DRF/IRFU


There are two types of instruments to observe gravitational waves (GW) at low frequency: space-based interferometer in the milliHertz (mHz) band, and Pulsar Timing Array (PTA) in the nanoHertz (nHz) band. They are complementary either by observing two parts of the same sources as for stochastic backgrounds or two parts of the same population of sources as for massive black hole binaries.
LISA is space-based GWs observatory which is planned for launch in 2035. It consists of three satellites in the free fall in the heliocentric orbit forming an equilateral triangle. Satellites exchange laser light forming multiple interferometers allowing to observe a plethora of astrophysical and cosmological sources of GWs. These sources include galactic white dwarf binaries, extreme mass-ratio inspirals, massive black hole binaries, stochastic backgrounds.
PTA is using the timing of millisecond pulsars to observe GWs. Millisecond pulsars emit about hundreds of radio pulses per second with very high regularity. GWs passing between pulsar and Earth, modifies the time of arrival of the pulses. The timing an array of pulsars, enable to make a galactic scale GW detector. Multiple radio-telescopes contribute to PTA, in particular the Nançay Radio-Telescope. In June 2023, 4 PTA collaborations announced the results of 20 years of pulsar timing: strong evidence for a GWs signal. The signal still needs to be characterized and its origin established. It could have been emitted by an ensemble of super-massive black holes or by processes in the primordial Universe. While the two observing systems are different, the data analysis methods are similar. A large parameter space needs to be sampled to extract overlapping sources and disentangle them from the non-stationary noises.
GWs are a new way to learn about fundamental physics. For example, we can test general relativity with the merger of super-massive black holes binary and Extreme Mass ratio Inspiral and test particle physics beyond the standard model, thanks to the detection of stochastic background (SGWB) from phase transitions in the early Universe. The candidate will work at the CEA-IRFU (Institut de Recherche sur les Lois Fondamentales de l'Univers) as part of a cross-disciplinary team conducting research into GWs. This activity ranges from instrumental involvement in the LISA mission to the astrophysical or cosmological consequences of exploiting the signals, via the development of algorithms, simulations and data analysis. IRFU is also involved in PTA-France and International PTA. Developing methods for detecting gravitational wave sources and deducing the associated physical consequences is at the heart of the proposed thesis topic. The candidate will have the opportunity to take an interest in all aspects of the host team's activity and to interact with each of its members. The main objectives of the proposed work are to develop data analysis methods for LISA, taking advantage of developments in PTA and LISA, and to study the synergy between LISA and PTA observations for fundamental physics, in particular with SGWBs and Massive Black Holes (MBHs). The methods developed can also be adapted and applied to real PTA data. The candidate will be a member of the collaborations LISA, PTA-France, EPTA and IPTA. He/she will interact with members of the Groupement de Recherche Ondes Gravitationnelles and collaborate with physicists from the Astroparticles et Cosmologie (APC) laboratory. He will present his results within the LISA and PTA consortiums and at international conferences.
Studying inflation with quasars and galaxies in DESI

SL-DRF-24-0627

Research field : Astrophysics
Location :

Service de Physique des Particules (DPHP)

Groupe Cosmologie (GCOSMO)

Saclay

Contact :

Etienne Burtin

Christophe YECHE

Starting date : 01-10-2024

Contact :

Etienne Burtin
CEA - DRF/IRFU/DPHP/GCOSMO

01 69 08 53 58

Thesis supervisor :

Christophe YECHE
CEA - DRF/IRFU/SPP/Bao

01-69-08-70-50

Measurements of the statistical properties of the large-scale structure (LSS) of the universe provide information on the physics that generated the primordial density fluctuations. In particular, they enable us to distinguish between different models of cosmic inflation by measuring primordial non-Gaussianity (PNG), the deviation from the initial conditions of the Gaussian random field.

Our strategy for studying LLS is to use a spectroscopic survey, DESI, whose instrument was commissioned at the end of 2019. DESI will observe 40 million galaxies and quasars. Observations take place at the 4-m Mayall telescope in Arizona. In the spring of 2021, the project began a five-year period of uninterrupted observations, covering a quarter of the sky.

For this thesis project, LSS are measured with two tracers of matter: very luminous red galaxies (LRG) and quasars, very distant and very luminous objects. These two tracers enable us to cover a wide redshift range from 0.4 to 4.0.

During the first year of his/her thesis, the student will contribute to the final analysis of the first year of DESI observations. In particular, he/she will study LSS with quasars and galaxies (LRG). His/her work will also involve assessing all possible sources of bias in the selection of quasars and LRGs that could contaminate a cosmological signal. In a second phase, the student will develop a more sophisticated analysis using three-point statistics such as the bispectrum with an extended sample to the first three years of DESI observations.

 

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