Galaxy formation and evolution

Three colour (BVI) image of a distant overdense region of galaxies taken by the Hubble Space Telescope. The image is focused on a spiral galaxy similar to the Milky Way but located at z = 1, i.e. 8 billion years ago. Twice the mass of the Milky Way, it has a star formation rate thirty times higher due to the surrounding galaxy overdensity.

Observational Cosmology has reached an important turning point. After years of seeking the parameters that govern the evolution of the Universe, there seems to be increasing consensus in acknowledging the dominant influence of dark matter on baryons and that of dark energy on dark matter. Paradoxically, the behaviour of the two “dark” components that make up 95% of the energy content of the Universe is easy to model (dark matter is nondissipative and subject only to gravity, while dark energy acts as an anti-gravitational factor), even though our knowledge of their nature remains highly speculative. This has led to the scientific community’s leaning increasingly toward what has become the conundrum that best stands up to theoretical attack: the behaviour of baryons and the origin of the light we receive from stars, galaxies and galaxy clusters. It is now acknowledged that it is not possible to understand how galaxies form and evolve without using the entire electromagnetic spectrum to study their various components (stars, gasses and dust) in their different states (neutral, ionized, young/old, dense/not very dense).


Last update : 10/18 2005 (604)


A key for unsderstanding galaxy evolution
As part of an observing program carried out with the Hubble Space Telescope, a group of researchers from the “Service d’Astrophysique-Laboratoire AIM” of CEA-IRFU led by Anita Zanella discovered the birth cry of a massive star-forming clump in the disk of a very distant galaxy. This giant clump is less than 10 million years old, and it is the very first time that such a young star-forming region is observed in the distant Universe. This discovery sheds new light on how stars were born within distant ... More »
The hot gas found in stars produced by laser pulses
A major international collaboration [1], involving researchers from the CEA-IRFU Astrophysics Department, CEA-IRAMIS and CEA-DAM, has succeeded in measuring for the first time the effects of light absorption by nickel in high temperature plasmas similar to those found around Cepheid-type variable stars. These stars are important indicators of distance in the Universe. They exhibit a periodic pulsing behavior caused by sudden increases in the absorption of light by the hot gas surrounding the star. These variations ... More »
The most famous collision of galaxies decoded using ‘high-resolution’ simulations
‘High-resolution’ numerical simulations carried out by scientists at the Astrophysics Department of the CEA-Irfu/AIM  have just revealed that the most famous galactic collision ever, the Antennae collision, produces far more stars than observations suggested. When two galaxies meet, the resulting gas compression causes the ignition of new stars. Until now, it seemed that these new stars appeared only in high-density regions, mainly near the core of the collision. A computer re-creation of the ... More »
The giant gas ring in Leo, formed when two galaxies collided
An international team led by astrophysicists from the Lyon Observatory (CRAL, CNRS/INSU, Université Lyon 1) and the AIM laboratory (CEA-Irfu, CNRS, Université Paris 7) has just shed some light on the origins of the giant gas ring in Leo.  The astrophysicists were able to detect an optical counterpart to this cloud, which corresponds to stars in formation, using the Canada-France-Hawaii telescope (INSU-CNRS, CNRC, U. Hawaii). The scientists then carried out numerical simulations on the supercomputers ... More »
The dark galaxy may just be tidal debris (15 novembre 2007)
What is a galaxy ? Stars, gas, some dust and surrounding them an invisible dark matter halo. The discovery a few years ago of a so-called « dark galaxy »  devoid of its most famous component - the stars - raised a lot of interest in the public and among astrophysicists puzzled by a specimen which had not been predicted by classical models. A team from the Service d'Astrophysique (SAp) and laboratory AIM (CNRS, CEA-Saclay, Université Paris Diderot has used numerical simulations to show that ... More »
The role of dust unveiled by the ISOCAM camera Our understanding of the history of the universe, or more precisely of galaxy formation, has recently been subject to an important revision. It all started in 1995 with the launch of an infrared camera named ISOCAM onboard the ISO satellite, the Infrared Space Observatory, launched by the European Space Agency (ESA). One of the ajor goals of the ISOCAM camera ... More »
Quantification of the star-formation and black-hole growth rate in galaxies Until the middle of the last decade, mergers of galaxies and the star formation episodes triggered by these phenomena had been considered as a major, even dominant, phase in the cosmic history of the formation of stars. This view of galaxy evolution stemmed from the increasing (i) fraction of interacting galaxies as a function of redshift (measured by the density of galaxy pairs or morphological analysis) and (ii) bolometric luminosity of ... More »


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