Astronomy and Astrophysics – Astrophysics – Cosmology and Extragalactic Astrophysics
Scientific paper
2011-08-22
Astronomy and Astrophysics
Astrophysics
Cosmology and Extragalactic Astrophysics
15 pages, 13 figures, submitted to A&A
Scientific paper
Galaxies accrete their mass both from smooth accretion from the cosmic web, and through merging of smaller entities. We want to quantify the respective role of these two modes of accretion, which could control the morphological types of galaxies observed today. Multi-zoom cosmological simulations are used to estimate as a function of time the evolution of mass in bound systems, for dark matter as well as baryons. Baryonic content of dark matter haloes are studied. Merger histories are followed as a function of external density, and the different ways mass is assembled in galaxies, and the stellar component is accumulated are quantified. We find that most galaxies assemble their mass through smooth accretion, and only the most massive galaxies grow also significantly through mergers. The mean fraction to assemble mass through accretion is 77%, and through mergers 23%. We provide typical accretion histories for hundreds of galaxies: if the more massive galaxies are monotonously growing in mass, mainly through accretion, many medium-mass objects also cross mass-loss events through tidal stripping and evaporation. The time to assemble half of the mass, both in dark matter and in baryons, is a decreasing function of mass, which is compatible with the observations of downsizing. At every epoch in the universe, there exist small-mass galaxies forming stars actively, while massive galaxies form their stars in a reduced period, at half the universe age.
Combes Francoise
L'Huillier Benjamin
Semelin Benoit
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