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Title: Galaxy populations in clusters and proto-clusters
Authors: Contini, Emanuele
Supervisore/Tutore: Borgani, Stefano
Cosupervisore: De Lucia, Gabriella
Issue Date: 20-Mar-2014
Publisher: Università degli studi di Trieste
The aim of my Thesis is to explore the physical properties of the galaxy population in clusters and proto-clusters. A large number of physical processes
plays an important role in the formation and evolution of galaxies: cooling, that allows the condensation of gas in the centre of dark matter haloes;
star formation, that converts cold gas in stars; feedback from Active Galactic Nuclei (AGN), that prevents the gas in the central regions of haloes
from "over-cooling"; feedback from Supernovae, which liberates energy in the surrounding, mixing the gas and enriching it with heavy metals.
Galaxy clusters are special environments in which additional important processes take place, and play an important role in the evolution
of the cluster galaxy population. Galaxy merging, harassments, tidal interactions, ram pressure stripping and strangulation are all processes acting
in dense environments such as clusters of galaxies.

I will take advantage of a {\it state of the art}-semi-analytic model of galaxy formation and of a set of 27 high-resolution dark matter only simulations:
the semi-analytic model is based on physically motivated and observationally constrained prescriptions for the physical processes listed above and makes
use of merger-trees extracted from the simulations to generate mock catalogues of galaxies.
First, I make use of this set of simulations to carry out a statistical study of dark matter substructures. In the framework of modern theories of galaxy
formation, dark matter substructures can be considered as the birth-sites of luminous galaxies.
Therefore, the analysis of subhaloes, and in particular of their mass and spatial distributions,
merger and mass accretion histories, provides important information about the expected properties of galaxies in the framework of hierarchical galaxy
formation models. I have studied the amount and distribution of dark matter substructures within dark matter
haloes, focusing mainly on the measured properties of subhaloes as a function of the mass and physical properties of their parent haloes, and redshift.
I show that the fraction of halo mass in substructures increases with increasing mass, reaching $10 \%$ for haloes with mass of the order
of $10^{15} \,M_{\odot} \hm$. The scatter in the relation is driven by halo concentration, with less concentrated haloes having
larger fractions of mass in substructures. Most of this mass is locateted in the external regions of the parent haloes, in relatively few,
but massive subhaloes, thus giving rise to a mass segregation which appears to be stronger at increasing redshift. Tidal stripping is
found to be the process responsible for that. In fact, haloes that are more massive at the time of accretion, and that are supposed to host more
luminous galaxies, are brought closer to the centre on shorter time-scales by dynamical friction, and therefore suffer of a more significant stripping.
The results confirm that the main properties of galaxies, such as luminosity or stellar mass, are related to the mass of subhalos at infall, as found
in previous studies.. The main results discussed in this part of the Thesis have been published in Contini et al. (2012), MNRAS.420.2978C.

In a second part, I describe the implementation of physical processes responsible for the generation of the Intra-Cluster Light (ICL)
in the available semi-analytic model, that, in its original form, does not account for them. The inclusion of these physical processes
is, thus, an important improvement of the model.
I take advantage of this upgrade of the model to investigate the origin of the ICL and to understand how the main properties of galaxies change
with respect to a model that does not include these additional prescriptions. I find the fraction of ICL in groups and clusters predicted by the model
to range between $10 \%$ and $40 \%$, with a large scatter and no halo mass dependence. Large part of the scatter on cluster scales is due to a range
of dynamical histories, while on smaller scales it is mainly driven by individual accretion events and stripping of relatively massive satellites, with mass of the order
of $10^{10.5} \, M_{\odot} \hm$, found to be the major contributors to the ICL. The ICL forms very late, below $ z \sim 1$ and a non
negligible fraction (between $5 \%$ and $25 \%$) has been accreted during the hierarchical growth of haloes. Moreover, the ICL is made of stars
which cover a relatively large range of metallicity, with the bulk of them being sub-solar, in agreement with recent observational data. The
main results of this analysis have been submitted to MNRAS (Contini et al. 2013).

In the last part of the thesis, the updated model is used to investigate the properties of the galaxy population in proto-cluster regions.
The work is still in progress. I am testing the predictions of the semi-analytic model and comparing them with observations
in terms of properties such as galaxy colours, star formation and stellar mass. A preliminary analysis of one very massive proto-cluster region shows that
the galaxy population gets red and tend to cluster around the most massive galaxy as time goes by.
There are, in literature, only a few attempts to probe such peculiar regions of the Universe from a theoretical point of view. The novelty of this
work lies in the connection between massive clusters observed in the local Universe and the proto-cluster regions from which they have formed.
I will try to define what a proto-cluster region is, and how it looks like, by studying the main properties of
progenitors it contains. Specifically, I will investigate the spatial and velocity distributions of galaxies in simulated proto-clusters, looking
at the red and blue galaxy distributions in these regions, as well as at BCG and satellite properties as a function of redshift. The main results of
this work will be the subject of a paper in preparation.
Ciclo di dottorato: XXV Ciclo
metadata.dc.subject.classification: SCUOLA DI DOTTORATO DI RICERCA IN FISICA
Keywords: Galaxy formation clusters
Language: en
Type: Doctoral Thesis
Settore scientifico-disciplinare: FIS/05 ASTRONOMIA E ASTROFISICA
NBN: urn:nbn:it:units-12248
Appears in Collections:Scienze fisiche

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