University of Groningen Chemical analysis of the Fornax dwarf galaxy Letarte, Bruno IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite from it. Please check the document version below. Document Version Publisher's PDF, also known as Version of record Publication date: 2007 Link to publication in University of Groningen/UMCG research database Citation for published version (APA): Letarte, B. (2007). Chemical analysis of the Fornax dwarf galaxy. [s.n.]. Copyright Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons). The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license. More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne- amendment. Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. Download date: 08-10-2021 Rijksuniversiteit Groningen Chemical Analysis of the Fornax Dwarf Galaxy Proefschrift ter verkrijging van het doctoraat in de Wiskunde en Natuurwetenschappen aan de Rijksuniversiteit Groningen op gezag van de Rector Magnificus, dr. F. Zwarts, in het openbaar te verdedigen op vrijdag 30 maart 2007 om 14.45 uur door Bruno Letarte geboren op 12 juni 1976 te Québec, Canada Promotor: Prof. dr. E. Tolstoy Copromotor: Dr. V. Hill Beoordelingscommissie: Prof. dr. M. Spite Prof. dr. P. C. van der Kruit Prof. dr. J. W. Pel ISBN 90-367-2927-0 ISBN 90-367-2928-9 (electronic version) In the beginning the Universe was created. This has made a lot of peo- ple very angry and has been widely regarded as a bad move. –Douglas Adams Cover page – Fornax Dwarves, by Jesse Giroux Contact information: Bruno Letarte [email protected] [email protected] This thesis has been funded by: With support from: LKBF Leids Kerkhoven-Bosscha Fonds Contents 1 Introduction 9 1.1 The Cosmological Importance of Dwarf Galaxies . 9 1.2 The Formation of the Elements . 11 1.3 Abundances in Galaxies . 12 1.3.1 The Milky Way . 13 1.3.2 The Magellanic Clouds & Dwarf Galaxies . 14 1.4 The DART project . 15 1.4.1 Photometry . 15 1.4.2 Spectroscopy . 15 1.4.3 This Thesis . 17 2 Fornax and the Local Group 19 2.1 Dwarf galaxies in the Local Group . 19 2.2 Fornax dSph . 21 2.3 Globular Clusters in Fornax . 24 3 Using stellar atmospheric models ... chemical abundances 27 3.1 Describing the stellar atmosphere . 27 3.1.1 The flux . 28 3.1.2 The absorption coefficient . 30 3.1.3 Stellar atmospheric models . 35 3.2 Determining Stellar Atmospheric parameters . 35 3.2.1 Effective Temperature (Teff )...................... 35 3.2.2 Surface Gravity (log g)......................... 36 3.2.3 Metallicity . 39 3.2.4 Microturbulence velocity . 39 3.3 The abundance determination . 39 3.3.1 Measuring the equivalent widths . 40 3.3.2 The Stellar Models used . 40 3.3.3 Computing the abundances . 42 3.4 The line list . 43 3.4.1 Building a line list . 43 vi CONTENTS 3.4.2 The line by line selection . 45 4 Abundances with the FLAMES multi-fibre instrument 47 4.1 UVES vs FLAMES . 48 4.1.1 UVES . 49 4.1.2 FLAMES . 49 4.2 The FLAMES Spectra . 50 4.2.1 Extracting, calibrating . 50 4.2.2 Combining . 50 4.2.3 Determining the radial velocities (Vrad) . 52 4.2.4 Measuring the Equivalent Widths . 52 4.2.5 Cleaning up the spectra . 56 4.3 Selecting our stellar parameters . 57 4.3.1 Photometric gravity . 57 4.3.2 Photometric Teff ............................ 57 4.3.3 Iterating on the parameters . 62 4.3.4 Precision and error estimates . 65 4.4 Systematics and corrections . 68 4.4.1 Systematics . 68 4.4.2 Hyperfine splitting correction . 71 Appendix 4.A Large tables . 72 5 HR spectroscopy in Fornax Globular Clusters 77 5.1 Introduction . 78 5.2 Observations . 79 5.3 Data Reduction and Analysis . 81 5.4 Interpretation . 85 5.4.1 The Iron abundance . 85 5.4.2 The Alpha elements . 86 5.4.3 Deep mixing pattern . 89 5.4.4 Iron-peak elements . 90 5.4.5 Heavy elements . 92 5.5 Conclusions . 95 Appendix 5.A Large tables . 97 6 HR spectroscopic study of Fornax Field Stars 105 6.1 Sample selection . 106 6.2 Results . 107 6.2.1 Iron abundance . 107 6.2.2 Alpha Elements . 108 6.2.3 Iron peak elements . 113 6.2.4 Deep-mixing pattern . 114 6.2.5 The Na-Ni relationship . 115 6.2.6 Heavy elements . 116 6.3 Discussion . 120 6.3.1 Comparison of Fornax and Sculptor . 121 6.3.2 Age and [Fe/H] . 122 6.4 Conclusions . 123 CONTENTS vii Appendix 6.A Large tables . 124 7 Conclusions 141 7.1 New Data Reduction and Analysis Techniques . 141 7.2 The Fornax Globular Clusters . 142 7.3 Fornax Field stars . 142 Bibliography 145 Nederlandse samenvatting 151 Résumé français 155 Acknowledgements 159 Chapter 1 Introduction warf galaxies are in principle the most simple and straightforward type of galaxy D and their study can be used to test numerous theories of the formation and evolution of stars and galaxies in a range of environments. This thesis concentrates on the detailed study of the chemical elements in individual stars in the nearby dwarf spheroidal galaxy, Fornax. A dwarf spheroidal galaxies are small roughly spherical galaxies that are typically found in the vicinity of larger galaxies, such as the Milky Way. They typically do not have any ongoing star formation, nor to they appear to have any gas associated to them. The abundance ratios of different elements in individual stars with a range of ages provide a detailed insight into the various chemical enrichment processes (e.g., supernovae, stellar winds) which in turn improves our understanding of the global processes of formation and evolution of a galaxy as a whole. 1.1 The Cosmological Importance of Dwarf Galaxies The most straightforward model of galaxy formation is that all galaxies form in the early Universe in a rapid collapse scenario (so called monolithic collapse, Eggen, Lynden-Bell, & Sandage 1962). These galaxies then evolve solely by changing their gas mass into a stellar mass with time. This model assumes that the majority of the mass of all galaxies was in place at their formation. However this basic picture was updated (e.g., Searle & Zinn 1978) to a model which assumes that galaxies are not formed in a single collapse, but that they are built up in time from smaller fragments. This theory came in parallel with the very successful “cold dark matter” (CDM) vision of structure formation in the Universe which assumes that the dark matter content of a galaxy is built up through the continuous accretion of small clumps, to build up the galaxies and clusters of galaxies we see today (e.g., White & Rees 1978; Navarro, Frenk, & White 1995). If we take the CDM model of structure formation and assume that the ratio of bary- onic to dark matter is roughly constant and known then this naturally results in the concept of numerous “building blocks”, or small galaxies, which are continuously being accreted onto larger galaxies over the history of the Universe. These small galaxies, with 10 chapter 1: Introduction a similar mass to the dwarf galaxies we see today, might act as stellar nurseries, creating the stars we see in the Milky Way (MW) today. Stars within the Galactic halo are some of the oldest objects ever observed and they should be representative of the earliest star formation in the Local Group (LG). These stars either formed in the proto-Milky Way or they may have formed in smaller satellite galaxies that were accreted to the Milky Way at a later time. CDM based models thus suggest that a considerable fraction of the stars in the Milky Way today should have formed in smaller building blocks. For example, the Sagittarius dwarf galaxy behaves exactly like a CDM building block, showing signs of being tidally disrupted and merging in its entirety into the Milky Way (Ibata et al. 1994). As required by the CDM view of the Universe small galaxies do appear to be dark matter dominated (e.g., Mateo 1998). Observations of dwarf spheroidal galaxies in the Local Group, such as Fornax dSph, suggest that dwarf galaxies must be considerably 9 10 more massive than the visible mass would suggest (e.g., ∼ 10 − 10 M , as compared 7 8 to visible masses of ∼ 10 − 10 M ), (Mateo et al. 1991; Walker et al. 2006; Battaglia et al. 2006). However there are inconsistencies in the predicted properties of the DM profiles of the observed dwarfs and the predictions of CDM (e.g., Wilkinson et al. 2006). It also appears that the properties of the stellar populations, the dark to baryonic matter ratio, and the kinematic properties of dwarf galaxies we see today are inconsistent with the requirements of building blocks of the Milky Way, i.e., adding together all the small galaxies we see today, or at any time in the past, will not result in a galaxy like the Milky Way (e.g., Shetrone et al.