# Approches semi-analytiques et numériques de la formation des halos de matière

Abstract : Galaxy formation and evolution, particularly in cluster environment, are studied from a theoretical point of view.
Assuming that cold dark matter (DM) is the dominant component of the Universe, DM halos form first, the less massive earlier, those with larger masses later, by merging of smaller objects. Galaxies form from the baryonic gas within DM halos, and they evolve with and within them. To study galaxy formation it is therefore necessary to describe the history of both dark and baryonic matter.
For the DM component, we first discuss a model based on the linear theory of the growth of density fluctuations in the Universe. The model (proposed by Rodrigues & Thomas 1996 and called the "Merging Cell Model") has been completely re-coded, applied to a SCDM cosmology, and analysed in many details. It is particularly suitable to study local clusters of galaxies, and the population of Lyman-break galaxies at redshift $z\simeq 3$.
To obtain a more reliable description of the DM halos merging history, we have then dealed with numerical simulations. In particular, we have re-simulated at high resolution 10 massive DM halos, that, under our working assumptions, correspond to the sites hosting galaxy clusters. The resimulation technique is carefully described, and its main advantages and drawbacks are stressed. It allows to precisely reproduce the selected halos, but of course, in many more details. The results of the 10 massive halos resimulations are presented, and they are the starting point for the next step.
The physical processes acting on the baryonic component within DM halos, and driving galaxy formation and evolution, are described by means of the hybrid model "GALICS". The combination of this technique with the high resolution resimulations of the 10 massive halos, allows us to describe hierarchical galaxy formation in clusters. A special attention is given to the effects of the dynamical processes thought to be particularly important in the cluster environment (dynamical friction, ram pressure stripping and direct collisions). Ram pressure stripping makes galaxies redder and the colour--magnitude relation thinner, in a better agreement with observations. It has smaller effects on galaxy morphology, that is mainly affected by the rate of direct mergers. On average, more massive clusters have more luminous and redder galaxies, as well as a higher fraction of ellipticals, with respect to less massive clusters. This holds both at the present time, and at redshift $z=0.5$, where galaxies are bluer, on average. Our (preliminary) results suggest that the bright end ($M_B \lsim -17$) of the luminosity function is steeper in high mass clusters than in less rich systems.
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https://tel.archives-ouvertes.fr/tel-00003165
Contributor : Barbara Lanzoni <>
Submitted on : Thursday, July 24, 2003 - 6:49:11 PM
Last modification on : Wednesday, December 9, 2020 - 3:05:26 PM
Long-term archiving on: : Tuesday, September 11, 2012 - 9:15:11 PM

### Identifiers

• HAL Id : tel-00003165, version 1

### Citation

Barbara Lanzoni. Approches semi-analytiques et numériques de la formation des halos de matière. Cosmologie et astrophysique extra-galactique [astro-ph.CO]. Université Paris-Diderot - Paris VII, 2000. Français. ⟨tel-00003165⟩

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