Semi-analytical galaxies in the multidark-universe.A perspective on the evolution of the most luminous and massive galaxies throughout cosmic history

Resumen

Understanding the formation and evolution of galaxies within a self-consistent cosmological context is one of the outstanding and most challenging topics of astrophysics. This dissertation is dedicated to investigating the concepts of galaxy formation with cosmology, in particular, the formation of large-scale structures and the assembly and evolution of their associated galaxies over cosmic time. This forms part of a vibrate and innovative field of research spanning all imaginable scales from The Big Bang to the Milky Way Galaxy with its many satellites. Over the last few decades a lot of effort has been invested into the development of models which can produce statistically significant sets of galaxy properties in a computationally efficient way. These models included the population of dark matter halos using simplified phenomenological treatments of baryonic processes and coarse-graining the properties of galaxies. As a result, relevant equation systems can be solved more efficiently – a semi-analytical model (SAM) was born. The MultiDark-Galaxies was an ambitious project dedicated to the release of galaxy catalogues from three different SAMs: Galacticus, SAG, and SAGE; run on the MultiDark Planck 2 N-body simulation covering a cubic volume of 1h−1 Gpc as part of this thesis work. To this point, the released galaxy catalogues remain one of the largest of their kind based on SAMs. We perform a comparison of the outputs of the three models and their conformity with fundamental galaxy properties derived from observations. Each model of galaxy formation has its unique recipe followed by individual calibration and tuning, therefore we highlight their differences and similarities. We demonstrate further that SAMs are an exceptional resourceful method of studying statistically significant samples of galaxy properties. We identify modelled galaxies from Galacticus, which show similar properties as observational samples and therefore are truly comparable with luminous red galaxies (LRGs) from e.g. SDSS at z ∼ 0.1 or BOSS-CMASS at z ∼ 0.5. We extract CMASS-mock samples from Galacticus using the original photometric selection as well as alternative methods mimicking such a selection. We study these mock samples in detail and find correlations of properties related to star formation: (specific) star formation rate, gas-phase metallicity ZCold , and cold-gas fraction MCold /M∗ , but also properties such as the halo mass M200c or the black hole mass MBH ; with the large-scale structure environment e.g. filaments or knots. We emphasise that, the bimodalities found in the properties of Galacticus’ CMASS-mocks, manifesting themselves as two distinct populations, could provide insights in the galaxy evolution in the context of the origin of the fundamental luminosity/mass-metallicity relation, merger- induced star formation, or “downsizing”. Our results may further challenge the paradigm that the large-scale environment does not influence the galaxy formation and predictions on the evolution of a galaxy inside its halo can be derived only from the halo mass and the occupation distribution, also know as the galaxy assembly bias. We trace the progenitors of Galacticus’ LRG-samples at low redshift to z ∼ 0.5 and identify 20% of them as CMASS. We show further the full mass growth history of the progenitors of the most diverse populations, red and blue, found in the CMASS-mock of Galacticus. We find that those samples have distinct properties, cluster differently, and have been assembled at different cosmic times, most probably throughout different evolutionary paths. We will conduct further analyses in order to confirm the possible detection of a galaxy assembly bias signal in our SAM.