Galaxias virtuales en simulaciones cosmológicas: morfología, dinámica y evolución

“VIRTUAL GALAXIES IN COSMOLOGICAL SIMULATIONS: Morphology, Dynamics and Evolution” The work carried out in this Thesis is part of the field of Numerical Cosmology and focuses on the study of the characteristics, evolution and differentiation of galaxies obtained from cosmological simulations. Numerical cosmology is the only laboratory that allows us to form galaxies with different "cosmological ingredients" and study their evolution, distinguishing which are the most relevant physical processes in their formation. The advantage of cosmological simulations is that they offer the possibility of controlling and monitoring the evolution of the simulated system at all times. Galaxies are the basic organizing components in the structure of the Universe. They are the link between the large-scale structure of the Universe and the most basic luminous components, since they are found populating the clusters of galaxies, the walls and the filaments but, in turn, they are formed by the stars and all the ingredients that are found in the Universe (gas, dust and dark matter). Its internal dynamics and the relationship with its morphology, its composition, its ability to form stars and the relationships between them continue to be a current issue in the study of cosmological evolution (Somerville & Davé, 2015; Wechsler & Tinker, 2018). In order for the observables of the virtual galaxies to be as faithfully comparable as possible to the observational plane, a whole series of observational spectral information has been included in the structures generated by the cosmological code through its stellar particles. MILES and MIUSCAT libraries (Vazdekis et al., 2012; Ricciardelli et al. 2012). In order to identify the different galactic structures and extract some of their characteristics without losing the evolutionary information of these structures, work has been done improving some existing tools and developing others. All of this aimed at treating virtual galaxies in a similar way to how real galaxies are treated in an observational analysis. The main lines of research followed in this work are, therefore, (i) obtaining images of the simulated galaxies directly comparable with the observations, (ii) development of analysis software capable of obtaining observable characteristics of said galaxies and (iii) ) to relate the dynamic and morphological characteristics of synthetic galaxies with their formation history throughout their evolution in order to better understand the processes that lead early-type galaxies to have the dynamics and morphology that they present today. The synthetic galaxies analyzed in this Thesis have been obtained from the results of the simulations carried out with the MASCLET cosmological code (‘Mesh Adaptive Scheme for CosmologicaL structurE evoluTion’) (Quilis, 2004). This hydrodynamic code for cosmological applications based on an Adaptive Mesh Refinement (AMR) scheme allows gas to be described as a fluid by discretizing it on a mesh. For the description of dark matter and particles, he uses an 'N-body' scheme. The HALMA finder (‘HALo finder for MAsclet’) is used to obtain virtual galaxies from among the results of the cosmological simulation carried out by MASCLET. As its name indicates, it is a stellar halo search engine specific to the MASCLET cosmological code and is based on the 'Friends-of-friends' (FoF; Davis et al., 1985) algorithm. Part of the work developed in this Thesis is to expand the capacity of HALMA allowing to obtain morphological and dynamic characteristics of the halos found (in the case of the present study the virtual galaxies analyzed) as well as their evolutionary history. Finally, the MIUSCAT stellar population synthesis models (Vazdekis et al., 2012b; Ricciardelli et al., 2012) have been used to “brighten” the virtual galaxies obtained, thus transforming physical quantities into observables. These models are an extended version of the MILES models (Vazdekis et al., 2010) and the CaT models (Vazdekis et al., 2003). Once the sample of virtual galaxies within a simulated volume of 44Mpc has been obtained, the work carried out has focused on the analysis of the most massive ones, those that at zero redshift have a stellar mass M_{*} > 10^{ 11}M_{sun} and are not in a merger process. Finally, a sample of 21 virtual galaxies that meet these conditions is obtained. One of the analyzes carried out consists of studying the characteristics of the sample according to three broad criteria: (i) the dynamic, (ii) the evolutionary and (iii) the morphological. For the dynamic criterion, one-dimensional profiles are used to calculate (V /σ). This quantity makes it possible to separate the sample into two groups, the fast rotors and the slow rotors. The second criterion used to study the galaxies in the sample is evolutionary. Through the study of the evolutionary history of galaxies, they are separated into two large categories: galaxies that have suffered at least one collision and those with a smooth evolution that have not suffered any collisions recognized by the halo finder. Finally, the third criterion used to order the sample is morphology. To do this, the light profile of each object is adjusted to a Sérsic profile, separating the sample into ellipticals or spirals. The conclusion of this analysis is that the evolutionary history (mergers with other galaxies) of a galaxy is mainly responsible for its current appearance, more than its morphology or dynamics. In this way, the galaxies that present a greater number of interactions with other galaxies are also the most massive in the sample and those that present the highest metallicity gradients. Another of the analyzes refers to the star formation history ('Star Formation History') of the galaxies in the sample. From this study it is concluded that mergers with other galaxies contribute only a minority fraction (10%-50%) of the total mass of the galaxy, with most of the stellar component formed 'in situ'. It is also verified that stellar particles Embedded, originating from other galaxies or from the medium, are significantly older (∼ 3 Gyr) and, on average, less metallic (0.1 dex) than those that form within the main branch of the galaxy. In the sample used, it is observed that most of the galaxies that present mergers (10 of the 11) can be classified as dissipative mergers with a lot of star formation. It is also observed that galaxies that have not undergone major collisions contain notable percentages of accreted stellar material. This material comes from the medium or from small stellar halos not identified by the search engine. In the virtual galaxies analyzed in this study, the accreted stellar component occupies mostly the outermost regions, specifically, the mass-half radius of the accreted material is ∼1.5 times the mass-half radius of the stellar material formed 'in situ'. '. Finally, the studied galaxies show a factor of ×2 − ×3 of stellar overproduction, this overproduction can be partly explained by the resolution limit of the cosmological simulation.