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Formation of Disc Galaxies from Cosmological Simulations: Galactic Outflows and Chemical Evolution

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Formation of Disc Galaxies from Cosmological Simulations: Galactic Outflows and Chemical Evolution Scuola Internazionale Superiore di Studi Avanzati - Trieste Formation of disc galaxies from cosmological simulations: galactic outflows and chemical evolution Author: Milena Valentini Supervisors: Prof. Stefano Borgani, Prof. Alessandro Bressan, Dr. Giuseppe Murante International School for Advanced Studies SISSA/ISAS A thesis submitted in fulfilment of the requirements for the degree of Doctor Philosophiae in ASTROPHYSICS and COSMOLOGY October 2018 SISSA - Via Bonomea 265 - 34136 TRIESTE - ITALY To Nicola Abstract In this Thesis, I study the formation of late-type galaxies and the role that feedback from stars and supermassive black holes (SMBHs) plays in galaxy evolution across cosmic time. By carrying out cosmological hydrodynamical simulations, I investigate how different processes, such as the cosmological gas accretion from the large scale environment, star formation and chemical enrichment, stellar and AGN (Active Galactic Nucleus) feedback, affect the early stages of forming galaxies and contribute to determine their present-day properties. Driven by the challenging task of simulating late-type galaxies with a limited bulge and a dominant disc in a cosmological context, I study the impact of galactic outflow modelling on the formation and evolution of a disc galaxy. I find that galactic outflows regulate the timing of gas accretion and determine the star formation history of the forming galaxy. Also, I quantify the strong interplay between the adopted hydrodynamical scheme and the sub-resolution model describing star formation and stellar feedback. Throughout this Thesis, I devote particular emphasis to connect chemical evolution and gas dynamics, in order to interpret observations of metal abundance in the interstellar medium (ISM) and circumgalactic medium (CGM). I investigate the metal content of gas and stars, and explore how the variation of the essential elements contributing to define the model of chemical evolution determine final metal abundance trends. The investigation that I present is guided by observations and focusses on the results at redshift z = 0, with particular emphasis on the role played by the high-mass end of the IMF. Moreover, I introduce a novel methodology to generate synthetic stars from star particles. The technique that I developed takes properties of star particles from simulations as input and allows to obtain a catalogue of mock stars, provided with photometric properties, whose characteristics are drawn from the input features. The ultimate goal of this method is to translate the populations of star particles of a simulation into stellar populations, thereby enabling a direct and accurate comparison with observations. This technique will be of paramount importance with ongoing survey data releases (e.g. GAIA and surveys of resolved stellar populations). Also, I investigate the role of AGN feedback in regulating the formation and evolution of late-type galaxies. I introduce a new model aimed at investigating the interaction between the central SMBH and the various gas phases which coexist in the ISM of the host galaxy. Contents Abstract List of Figures xiii List of Tables xvii List of Abbreviations xix Publication list xxi This Thesis1 1 Introduction3 I General background7 2 Late-type galaxies in the local Universe9 2.1 The diversity of the galaxy population . .9 2.2 Growth of cosmic structures . 13 2.3 Formation of disc galaxies: theoretical scenario . 17 2.4 Disc galaxies: observational results . 21 2.4.1 The multiphase ISM . 22 2.4.2 Scaling relations . 23 2.4.3 Stars and their metal content . 25 2.4.4 Galactic outflows . 28 2.4.5 AGN feedback . 30 vii 3 Simulating galaxies in a cosmological context 33 3.1 Numerical approach to astrophysics and the role of simulations . 34 3.2 Simulating galaxies: challenges . 37 3.3 The angular momentum problem . 41 3.4 Modelling ISM and sub-resolution processes . 43 II Methods 49 4 Numerical methods 51 4.1 Collisionless matter and gravity . 52 4.2 Hydrodynamics . 55 4.3 Smoothed Particle Hydrodynamics . 58 4.4 Successes and shortfalls of SPH . 63 5 The simulations setup 69 5.1 The code . 69 5.2 Improved SPH formulation . 72 5.3 The model of star formation and stellar feedback . 75 5.4 Additional physics: cooling and chemical enrichment . 81 5.5 Initial conditions . 83 III Results 87 6 On the effect of galactic outflows in cosmological simulations of disc galaxies 89 6.1 Numerical description matters . 90 6.2 Numerical models . 92 6.2.1 Coupling MUPPI with the improved SPH . 92 6.2.2 A new switch for AC . 94 6.3 Implementation of galactic outflow models . 95 6.3.1 FB1: Dalla Vecchia & Schaye model . 96 6.3.2 FB2: modified MUPPI kinetic feedback . 98 6.3.3 FB3: fixing the mass loading factor . 99 viii 6.4 The set of simulations . 102 6.5 Results . 104 6.5.1 The importance of the AC switch . 104 6.5.2 Effect of the new SPH scheme . 107 6.5.3 Changing the galactic outflow model . 118 6.5.3.1 Tuning the models . 118 6.5.3.2 Comparing results . 120 6.6 Discussion . 130 6.6.1 Effect of the resolution . 130 6.6.2 Parameter space of galactic outflow models . 136 6.7 Summary and Conclusions . 140 7 Chemical evolution of disc galaxies from cosmological simulations 143 7.1 Chemical evolution in simulations: an overview . 144 7.2 Numerical simulations . 147 7.2.1 The set of simulations . 148 7.3 Impact of IMF on the number of massive stars . 150 7.4 Results . 152 7.4.1 Main properties of the simulated galaxies . 153 7.4.2 Stellar ages and SN rates . 157 7.4.3 Metallicity profiles . 163 7.4.3.1 Stellar metallicity gradient . 163 7.4.3.2 Gas metallicity gradient . 167 7.4.4 Stellar α-enhancement . 169 7.4.5 Metals in and around galaxies . 176 7.4.6 Stellar yields . 178 7.5 Discussion and Conclusions . 180 ix 8 Colour-magnitude diagram in simulations of galaxy formation 183 8.1 The need for going from star particles to stars . 184 8.2 Cosmological simulations of a disc galaxy . 186 8.2.1 Simulations . 186 8.2.2 Main features of the simulated galaxies . 188 8.3 Building the stellar content of star particles: method . 189 8.3.1 Parent particle selection . 190 8.3.2 Generation of synthetic stars: the TRILEGAL Code . 192 8.3.3 Producing the star catalogue . 193 8.3.4 Construction of the CMD . 195 8.4 Observational data set for the comparison . 197 8.5 Results . 199 8.5.1 CMD from cosmological simulations . 200 8.5.2 Properties of synthetic stars . 202 8.6 Discussion . 208 8.6.1 Solar neighbourhood sampling variance . 208 8.6.2 Comparison with results from the GCS . 212 8.6.3 Comparison with the MDF of other surveys . 213 8.7 Summary and Conclusions . 214 9 AGN feedback in simulations of disc galaxies 217 9.1 AGN feedback in cosmological simulations . 218 9.2 AGN feedback modelling . 220 9.2.1 Introducing BHs: seeding and pinning . 220 9.2.2 AGN feeding . 222 9.2.3 Controlling BH accretion . 224 9.2.4 AGN feedback . 225 9.2.5 Including AGN feedback within MUPPI . 226 9.2.6 Coupling AGN feedback energy to a multiphase ISM . 228 9.2.6.1 Constant coupling parameters . 229 9.2.6.2 Locally varying energy coupling . 230 9.3 The suite of simulations . 231 x 9.4 Results . 234 9.4.1 Disc galaxies with AGN feedback . 235 9.4.2 BH evolution . 238 9.4.3 BH-galaxy coevolution . 244 9.4.4 Effect of BH seed mass . 251 9.4.5 Does AGN feedback affect metallicity profiles? . 254 9.4.6 Coupling AGN feedback energy according to ISM properties 259 9.4.7 Angular momentum dependent accretion . 262 9.5 Concluding remarks . 267 10 Conclusions and future perspective 271 Appendix 281 A Essentials of cosmology 283 A.1 Basics of our Universe . 283 A.2 Origin of cosmic structures . 286 A.3 The spherical collapse . 288 Bibliography 291 Acknowledgements 307 xi List of Figures 2.1 Elliptical and spiral galaxies . 11 2.2 Representative illustration of the Hubble diagram . 12 2.3 Temperature map of the CMB and the clustered matter distribution in the present-day Universe . 13 2.4 Cooling function . 17 2.5 Tully-Fisher, luminosity-size, and velocity-size scaling relations . 25 2.6 Correlations between BH mass and stellar mass of bulge, and BH mass and stellar velocity dispersion . 31 3.1 Morphology of simulated galaxies in the Aquila Comparison Project 45 3.2 Prominence of the stellar disc component in simulated galaxies . 46 5.1 Multiphase particle: cartoon . 75 5.2 Original galactic outflow model: cartoon . 80 5.3 Metal-dependent cooling function . 82 5.4 Zoomed-in initial conditions . 84 6.1 Phase diagram of all the gas particles of the AqC5-newH simulation 93 6.2 FB2 galactic outflow model: cartoon . 98 6.3 Phase diagram of gas particles of the AqC5-newH galaxy simulation with AC off . 106 6.4 Distribution of gas particles with AC off . 107 6.5 Impact of the hydrodynamic solver: gas and stellar density maps of simulations . 108 6.6 Impact of the hydrodynamic solver: star formation history . 109 6.7 Impact of the hydrodynamic solver: circularity of stellar orbits . 111 6.8 Impact of the hydrodynamic solver: mass accretion history . 112 6.9 Impact of the hydrodynamic solver: phase diagrams . 113 xiii 6.10 Impact of the hydrodynamic solver: radial profiles . 115 6.11 Impact of the hydrodynamic solver: Tully-Fisher relation and baryon conversion efficiency . 117 6.12 Galactic outflow models: gas density maps .
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