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Formation and Evolution of Galactic Discs

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ECOLE DOCTORALE ED352 : PHYSIQUE ET SCIENCES DE LA MATIERE Discipline : Astrophysique et Cosmologie Thèse présentée pour obtenir le grade universitaire de docteur Nicolas PESCHKEN Formation and evolution of galactic discs Soutenue le 03/11/2016 devant le jury : Philippe AMRAM Laboratoire d’Astrophysique de Marseille Directeur du jury François HAMMER GEPI Observatoire de Paris Rapporteur Olivier BIENAYME Observatoire Astronomique de Strasbourg Rapporteur Carlos GARCIA GOMEZ Universitat Rovira i Virgili Examinateur Albert BOSMA Laboratoire d’Astrophysique de Marseille Examinateur Evangelie ATHANASSOULA Laboratoire d’Astrophysique de Marseille Directeur de thèse Aknowledgments I first want to thank my supervisor, Lia Athanassoula, for following, helping and supporting me consistently during these three years of PhD. She has been very present and available for me, allowed me to study many different and interesting aspects of galaxy simulations, and I learned a lot by working with her. I would also like to thank the other people in our team, who were always very helpful when I needed it. Jean-Charles Lambert has been essential as the skill- full computer engineer of the group, and besides having developped or installed most softwares I was using, he has helped me countless times for fixing bugs or helping me with my codes, as I would drop by his office saying "It doesn’t work!". Sergey Rodionov has always been available to help me with physics issues or giv- ing me some of his codes to save time. I also want to thank Albert Bosma for helping me with my postodc applications, by patiently reviewing and correcting all my documents. I also thank Marie Treyer for taking the time to listen about my research progress, and caring about the good proceeding of my PhD. I would like to express my gratitude to the jury members Carlos Garcia Gomez, Philippe Amram and Albert Bosma for accepting to be part of my thesis commit- tee, and especially to François Hammer and Olivier Bienaymé for their careful reading of my thesis, as well as their useful comments. I want to thank all the PhD students, postdocs or interns, with which we would meet every day for lunch breaks, wich allowed me to chill out and stop thinking about work. They have truly become friends and have contributed very much to the excellent atmosphere I was feeling in the laboratory. Here are the names of some of them (I apologize for the ones I forgot) : Mario, Anna, Pedro, Miguel, David, Anna, Darko, Samuel, Javier, Ana, Marie, Axel, Deborah, Sergey, Grze- gorz, Arthuro, Loren, Francesca, ... Finally, a very special thanks Pauline for her love, support and patience during these three years. I asked her to follow me in the South for two years and she accepted without hesitation. She has always been here to hear me talk about my 3 PhD over and over again, in good and in bad times, and never complained once. I could not ask for more. 4 Contents Aknowledgments 3 List of Figures 8 Introduction 10 I. Study of simulated disc galaxies 14 1 Context 15 1.1 The Hubble sequence 15 1.1.1 Elliptical galaxies (Early Type) 15 1.1.2 Spiral galaxies (Late type) 16 1.1.3 Lenticulars 16 1.1.4 Irregulars 17 1.1.5 From early type to late type? 17 1.2 Disc galaxies 19 1.2.1 How they form 19 1.2.2 Bar 20 1.2.3 Bulges 20 1.2.4 Disc 22 2 Our simulations 26 2.1 Creating a disc galaxy from a major merger 26 2.1.1 Paper I 26 2.1.2 My contribution to Paper I 44 2.1.3 Beyond the three fiducial examples: whole sample 44 2.1.4 Merging period 46 2.2 Stellar migration 54 2.2.1 Presence of radial stellar migration 54 2.2.2 What causes this migration? 56 2.3 Bar pattern speed 59 2.3.1 What is the pattern speed? 59 2.3.2 Description of the Tremaine-Weinberg Method 59 5 2.3.3 Computing the pattern speed with the TW method in sim- ulations 60 2.3.4 Conclusion about the pattern speed 64 II. On the surface density profile of disc galaxies 65 3 Context 66 3.1 Observations 66 3.2 Bulge part 68 3.3 Bar 69 3.4 Disc part 70 3.4.1 Single Exponential 70 3.4.2 Downbending disc 71 3.4.3 Upbending disc 72 3.4.4 Disc types frequencies and Hubble sequence 73 4 Study of the density distribution in our simulations 75 4.1 Two-dimensional analysis 75 4.1.1 GALFIT 75 4.1.2 BUDDA 77 4.2 One-dimensional analysis 78 4.2.1 Fitting Procedure 78 4.2.2 Difficulties 80 4.3 Inner regions 84 4.3.1 Bulge 84 4.3.2 Bar 89 4.4 Disc part 91 4.4.1 Understanding the profile 91 4.4.2 Paper III: Linking the profile with angular momentum 96 4.4.3 Paper IV: Radial projected surface density profiles 110 4.4.4 Type III isolated 121 4.4.5 Comparison to observations: Scaling relations 126 4.5 Thick disc 130 4.5.1 Thickness of the disc 130 4.5.2 Thick disc radial profile 132 Conclusion 135 Perspectives 137 Bibliography 140 Appendix 151 A Merging morphology 152 6 B How to compute the circularity parameter ǫ 154 C How to compute the guiding radius 154 D Bar evolution over time 156 E Computation of the spin parameter λ 157 E.1 Whole System 157 E.2 One component 158 F Evolution of the radial density profile from type III to type II 161 Résumé 162 Abstract 164 7 List of Figures 1.1 Hubble Sequence 15 1.2 Color-magnitude diagram 18 1.3 Sombrero galaxy 19 1.4 Vertical distribution of a galaxy 24 2.1 Star Formation Rate as a function of time 48 2.2 Black hole mass as a function of time 50 2.3 Fraction of ǫbirth > 0.5 particles as a function of time. 95% method. 51 2.4 Fraction of ǫbirth > 0.5 particles as a function of time. Derivative method. 53 2.5 Migration in the Ri-Rf plane. 55 2.6 Mean migration as a function of the radius 56 2.7 Face-on view of inward migrating stars over time 57 2.8 Face-on view of outward migrating stars over time 58 2.9 Pattern Speed results: Bar constraint 62 2.10 Pattern speed results: two different times 63 3.1 Sérsic function for different indexes n 69 3.2 Surface brightness profiles: disc types 71 3.3 Surface brightness profiles: type II + III 73 3.4 Disc types as a function of Hubble type 74 4.1 GALFIT results: presence of a discy bulge 77 4.2 Radial density profile: Bar 81 4.3 Radial density profile: Spirals 82 4.4 Radial density profile: fit and spirals 83 4.5 Radial density profile: quality of the the fit and spirals 84 4.6 Radial density profile: 1 bulge fit 85 4.7 Radial density profile: 2 bulges fit 86 4.8 Radial density profile: Upbending end 87 4.9 Radial density profile: Fitting the upbending end 88 4.10 Radial density profile: Upbending end and vertical cut 89 4.11 Radial density profile: Fitting the bar 90 4.12 Radial density profile: Gas profile 91 4.13 Radial density profile: Gas profile fit 92 4.14 Gaseous - stellar breaks correlation 93 8 4.15 Star Formation Rate as a function of the radius 95 4.16 Spiral morphology and break 96 4.17 Scalelengths correlations with λ including low resolution simulations 108 4.18 Effect of orbit and spin on the computation of λ 109 4.19 Migration distance as a function of λ, for inward and outward migration110 4.20 Type III isolated galaxy profile 122 4.21 Type III isolated galaxies in λ correlations 123 4.22 Isolated galaxy type II profile underneath 124 4.23 Type III isolated galaxies in λ correlations, with an ǫ cut. 125 4.24 Comparison of scalelengths and break radius with observations 127 4.25 Comparison of scalelengths and break radius with observations, for isolated galaxies 127 4.26 Comparison to observations: break radius - inner scalelength 128 4.27 Comparison to observations: scalelengths and central surface bright- ness 129 4.28 Comparison to observations of scalelengths and break radius, for type III isolated galaxies 130 4.29 Vertical density profile 131 4.30 Thin and thick disc separation 132 4.31 Thick disc radial density profile 132 A.33 Merging periods: face-on views 152 A.34 Merging periods: face-on views 153 A.35 Bar evolution over time: face-on view 156 A.36 Bar evolution over time: radial density profile 157 A.37 Radial density profile transition from type III to II 161 9 Introduction The Milky Way has fascinated humanity for thousands of years, being very easy to observe in the night sky with its bright band shape. Already in the ancient Greece, philosophers such as Democritus (460–370 BCE) or Aristotle (384–322 BCE) were trying to understand what was this particular structure. They gave it the greek name Galaxias, which can be translated as Milky One, and the hypoth- esis of an agglomeration of distant stars was already proposed. Nervertheless, it was not until 1610 that this was finally proven by Galileo, using one of the first telescopes. The picture of the Milky Way being a rotating disc then first appears in 1750 with Thomas Wright, an english astronomer, as well as the idea that the solar system is part of it.
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