Garaldi, Enrico: From galaxies to the cosmic web and back: the interplay of different scales in galaxy formation and cosmic reionization. - Bonn, 2020. - Dissertation, Rheinische Friedrich-Wilhelms-Universität Bonn.
Online-Ausgabe in bonndoc:
author = {{Enrico Garaldi}},
title = {From galaxies to the cosmic web and back: the interplay of different scales in galaxy formation and cosmic reionization},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2020,
month = oct,

note = {The evolution of the Universe is primarily governed by gravity, that triggers the development of a complex web-like distribution of galaxies. The latter are embedded in larger structures, called haloes, mainly composed by an exotic form of matter that does not interact with light, and is therefore called dark. Within this cosmic web, astrophysical phenomena occur on a large variety of spatial scales. Although ubiquitous, the interaction between them is often neglected because of the difficulties in their simultaneous modeling. In this Thesis we employ advanced numerical simulations of structure formation in the universe to investigate three cases where this interplay is of primary importance, namely: the assembly bias, the radial acceleration relation and the epoch of cosmic reionization.
Assembly bias denotes the fact that dark matter haloes of the same mass have clustering properties that depend on their formation time. This effect is due to the cosmic environment of such haloes, that halts the accretion of new material in regions where the tidal field exerted by nearby structures is strong. Therefore, the assembly of objects strongly clustered is more efficiently suppressed. In this Thesis, we study the properties of satellite galaxies that reside within haloes with different assembly histories, and therefore cosmic environments. We show that their content is insensitive to the large-scale geometry of the matter distribution. However, the latter has a strong impact on the satellite dynamics, producing a preferentially-radial motion in objects embedded in a knot of the cosmic web, and isotropically-distributed velocities in region within filaments. We apply this knowledge to the satellites of the Milky Way and infer that our Galaxy must reside in a prominent filamentary structure.
Recent observations of a large sample of galaxies unveiled a tight correlation between the total radial acceleration experienced by bodies orbiting around the galactic center and the same quantity inferred only from the galactic baryonic content. Theoretical models of structure formation have been tested against this radial acceleration relation (RAR) only for large structures. Here, we predict for the first time the RAR of small satellite galaxies, opening up the possibility to test our knowledge of galaxy formation mechanisms in an uncharted territory. Additionally, we study the redshift evolution of this relation and its secondary dependence on physical properties of the satellites. We then make use of these results to devise an observational test that can distinguish between the standard cosmological model and one popular alternative theory, the Modified Newtonian Dynamics.
Finally, we study the role of quasars in the reionization of the Universe on the largest scales. We do so by simulating a reionization scenario where the ionizing photons production is dominated by quasars and compare it with one where galaxies are the main source of such photons. We show that, despite the peculiar emission properties of quasars, the former leads to global properties of the inter-galactic medium that are in agreement with observations. Additionally, we produce synthetic absorption spectra and use them to show that, in a quasar-dominated scenario, the properties of helium absorption features are incompatible with available observations. However, we also find indications that a modest contribution from quasars can explain the observed distribution of patches of inter-galactic neutral hydrogen. To unravel these apparently-controversial findings, we identify and investigate two promising methods that, using future observations, will enable a determination of the quasar contribution to cosmic reionization.},

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