Understanding how galaxies form, interact, and evolve comes largely from comparing theory predictions with observational data. Numerical simulations of galaxies provide the most accurate approach... Show moreUnderstanding how galaxies form, interact, and evolve comes largely from comparing theory predictions with observational data. Numerical simulations of galaxies provide the most accurate approach to testing the theory, as they follow the non-linear evolution of gas and dark matter in great detail and incorporate numerous baryonic processes, among which are energy feedback from supernovae (SNe) and Active Galactic Nuclei (AGN). In this thesis, we show the results of the development of the new model COLIBRE for cosmological simulations of galaxy formation that include a cold interstellar medium. First, we present a new SN feedback recipe developed for COLIBRE, whereby SN energy is injected into the gas in thermal and kinetic forms, and the total energy and momentum of the system of gas and stars are exactly conserved. Second, we conduct a detailed comparison of different ways in which SN energy is distributed in the gas environment around young stellar populations. Third, by using our simulation setup originally developed to test COLIBRE’s SN feedback, we show that the radioactive isotope Fe60 that has been detected on Earth is likely of SN origin. Finally, we present the calibration of the SN and AGN feedback of the COLIBRE model using machine learning. Show less
Following the Big Bang, structure in the Universe started collapsing under the force of gravity. This resulted in the formation of the first stars, galaxies and clusters of galaxies. The majority... Show moreFollowing the Big Bang, structure in the Universe started collapsing under the force of gravity. This resulted in the formation of the first stars, galaxies and clusters of galaxies. The majority of the baryonic mass in a galaxy cluster is part of the hot intracluster medium, which permeates the entire cluster As this medium cools down, it accretes onto the central galaxies where it triggers the formation of new stars. However, it also feeds the central supermassive black hole, creating an active galactic nucleus (AGN) that injects a large amount of energy into the intracluster medium again, resulting in a feedback cycle. This feedback cycle is an essential ingredient in the formation and evolution of galaxies. Using new high-resolution radio observations taken with the LOw Frequency ARray (LOFAR), we study AGN feedback in galaxy clusters in unprecedented detail, gaining insight into both the duty cycle of the AGN as well as the energy budget of the feedback cycle. Show less
Pérez-González, P.G.; Costantin, L.; Langeroodi, D.; Rinaldi, P.; Annunziatella, M.; Ilbert, O.; ... ; María Mérida, R. 2023
Galaxies in the local Universe fall into two main categories of spirals and ellipticals. In this Thesis, we explore the structural evolution of galaxies into this bimodal distribution. To do so, we... Show moreGalaxies in the local Universe fall into two main categories of spirals and ellipticals. In this Thesis, we explore the structural evolution of galaxies into this bimodal distribution. To do so, we study galaxies in the context of the Fundamental Plane, the tight scaling relation between galaxy size, kinematics and luminosity, which connects the structural and stellar population properties of galaxies. This work is built on a combination of observational data and theoretical models. Large spectroscopic surveys are used to construct a representative sample of massive quiescent and star-forming galaxies across 8 Gyr of cosmic time. We hence show that there is strong variation and evolution in the mass-to-light ratios of galaxies, due to evolution in the stellar populations. However, surprisingly, all galaxies lie on a single mass Fundamental Plane, which does not evolve with time. Cosmological simulations are used to assess the structural properties that may underlie the observed mass Fundamental Plane. Based on the simulations, we propose that this relation may originate from a systematic variation in the central dark matter content within galaxies as a function of their size and mass. Show less
Li, R.; Napolitano, N.R.; Roy, N.; Tortora, C.; La Barbera, F.; Sonnenfeld, A.; ... ; Liu, S. 2022
One of the major unresolved questions in astronomy is: how do galaxies form and evolve? In the local universe we can distinguish between actively star-forming and quiescent galaxies. Quiescent... Show moreOne of the major unresolved questions in astronomy is: how do galaxies form and evolve? In the local universe we can distinguish between actively star-forming and quiescent galaxies. Quiescent galaxies are typically the most massive, with elliptical morphologies and red optical colors. The mechanisms that cause star-formation in galaxies to be turned off, so that star-forming galaxies become quiescent, are not yet well understood. Using the FourStar Galaxy Evolution Survey (ZFOURGE), comprising near-infrared data of over seventy thousand galaxies, we aim to find and study the first quiescent galaxies. First we describe the data products of ZFOURGE. Then we present the discovery of 15 very massive quiescent galaxies over 12 billion years ago, when the universe was only 1.6 billion years old. The implication is that they must have formed extremely rapidly, with explosively high star-formation rates. They are very compact, and much smaller than nearby quiescent galaxies as well as equally distant star-forming galaxies. Considering number counts and average properties of star-forming galaxies at even earlier times, we speculate that their formation history may have included a dust-obscured star-burst, possibly also forming a dense stellar core. Finally, we present a study of star-forming galaxy kinematics 11 billion years ago. Show less
In this thesis we used numerical simulations to explore the role that chemistry plays in galaxy formation. Simulations of galaxies often assume chemical equilibrium, where the chemical reactions... Show moreIn this thesis we used numerical simulations to explore the role that chemistry plays in galaxy formation. Simulations of galaxies often assume chemical equilibrium, where the chemical reactions between ions and molecules have reached a steady state. However, this assumption may not be valid if the physical conditions of the gas are evolving rapidly. Therefore, we developed a chemical model to follow the non-equilibrium evolution of ions and molecules. We then incorporated this model into hydrodynamic simulations of galaxies. We ran simulations with different metallicities (i.e. different proportions of heavy elements) and UV radiation fields, first using our full non-equilibrium chemical model and then assuming chemical equilibrium. We found that the total star formation rate is higher at higher metallicity and for weaker radiation fields. In contrast, non-equilibrium chemistry does not strongly influence the total star formation rate or outflow properties of the galaxy. However, it does affect the abundances of individual chemical species, for example in molecular outflows. Finally, we explored the properties of molecular clouds in our simulations. At low metallicity, the molecular fraction of young clouds tends to be below equilibrium, as the molecules are still forming. This also affects the observable CO emission from young clouds. Show less
The question of how the first stars formed and assembled into galaxies lies at the frontier of modern astrophysics. The study of these first sources of cosmic illumination was transformed by the... Show moreThe question of how the first stars formed and assembled into galaxies lies at the frontier of modern astrophysics. The study of these first sources of cosmic illumination was transformed by the installation of new instrumentation aboard the Hubble Space Telescope during one of the final Space Shuttle missions in 2009. Hubble has since unveiled a population of ultra-faint galaxies seen just a few hundred million years after the Big Bang, an epoch often termed the Cosmic Dawn. This thesis presents pioneering observational studies of the first generations of galaxies, enabling an examination of their properties and the physics that governed the illumination of the early cosmos. Show less
In this dissertation we explore the effects that the processes associated with galaxy formation __ such as feedback - may have on the clustering of matter. We also explore the contribution of... Show moreIn this dissertation we explore the effects that the processes associated with galaxy formation __ such as feedback - may have on the clustering of matter. We also explore the contribution of matter in haloes to the clustering of all matter, the impact of halo shape and alignment on galaxy clustering, and constraining galaxy formation in semi-analytical modelling using the estimated correlation function. Show less
We study several aspects of the formation of galaxies, using numerical simulations. We investigate the influence of about thirty different sub-grid physics recipes for cooling, star formation,... Show moreWe study several aspects of the formation of galaxies, using numerical simulations. We investigate the influence of about thirty different sub-grid physics recipes for cooling, star formation, supernova feedback, AGN feedback etc. on the resulting galaxy populations with large SPH simulations. We investigate several parameters that quantify the environment of galaxies and present the strongest measure of halo mass and a new parameter that is insensitive to halo mass. We look at the effects of input physics and dust attenuation on the simulated luminosity functions and compare luminosity functions directly obtained from simulations, with those using observers' tools on mock images. Regardless of most parameters used for the mock image creation and the detection of sources, these two LFs agree well. The last chapter compares several ways of sampling stellar IMFs in clusters that follow a cluster mass function in order to see how the choice of CMF and sampling method influence the resulting integrated galactic initial mass function. The effects are only significant if the CMF extends as a steep power-law down to a few solar masses. We study the effects of these IGIMFs on the galaxies' integrated photometry and metal and O-star content. Show less
The first stars formed a few hundred million years after the Big Bang, when the Universe was only a small fraction of its present age. Their radiation transformed the previously cold and neutral... Show moreThe first stars formed a few hundred million years after the Big Bang, when the Universe was only a small fraction of its present age. Their radiation transformed the previously cold and neutral hydrogen that filled intergalactic space into the hot and ionised cosmic plasma that is observed today. This milestone in the history of the Universe is called the epoch of reionisation. Much about reionisation is still unknown. Computer simulations are one of the most promising theoretical tools to study reionisation. The wealth of high-quality data that will soon be provided by the next generation of telescopes, specifically designed to observe the reionisation event, make it a particularly exciting time to perform such simulations. The thesis "Simulating Cosmic Reionisation" presents TRAPHIC, a novel method to include the transport of ionising radiation emitted by the first stars in simulations of reionisation. TRAPHIC (TRAnsport of PHotons In Cones) is one of the first of a new type of radiative transfer methods that allow the accurate and efficient computation of the growth of ionised regions in representative models of the Universe that contain hundreds of millions of stars. First simulations that employ TRAPHIC on the Dutch national supercomputer Huygens demonstrate the importance of the concepts that underly its design. Show less
In this thesis I discuss recent observations of distant (z > 2) radio galaxies. There is strong evidence that radio galaxies are the progenitors of the brightest cluster ellipticals and are... Show moreIn this thesis I discuss recent observations of distant (z > 2) radio galaxies. There is strong evidence that radio galaxies are the progenitors of the brightest cluster ellipticals and are among the most luminous and massive galaxies at any epoch, allowing relatively detailed studies of their formation process out to large distances. Submillimeter emission has been detected in many, implying star formation rates of order 1000 Msun/yr over scales of tens of kpc, consistent with a scenario in which these galaxies are currently forming the bulk of their eventual stellar population. Many radio galaxies also host giant (~ 150 kpc) emission line nebulae. We obtaind very deep narrow-band Ly-a images for a select few of these. The observations show spectacular detail with a wealth of morphological structure, such as extended (~ 80 kpc) filamentary structures, giving insight in feedback processes during their formation. I discuss the possible origin and the ionization source of these halos in connection with the sub-mm results, and discuss possible implications for theories of galaxy formation. Show less
