UNIVERSIDAD DE CHILE FACULTAD DE CIENCIAS F´ISICAS Y MATEMATICAS´ DEPARTAMENTO DE ASTRONOM´IA SPATIALLY RESOLVED STAR FORMATION HISTORY OF MILKY WAY SATELLITES: THE CASE OF CARINA TESIS PARA OPTAR AL GRADO DE DOCTOR EN CIENCIAS, MENCION´ ASTRONOM´IA FELIPE ANTONIO SANTANA ROJAS PROFESOR GU´IA: RICARDO RODRIGO MUNOZ~ VIDAL MIEMBROS DE LA COMISION:´ JULIO CHANAME´ DOM´INGUEZ ANDRES´ ESCALA ASTORQUIZA GUILLERMO BLANC MENDIBERRI SANTIAGO DE CHILE ENERO 2016 RESUMEN DE LA TESIS PARA OPTAR AL GRADO DE DOCTOR EN CIENCIAS, MENCION´ ASTRONOM´IA HISTORIA DE FORMACION´ ESTELAR ESPACIALMENTE RESUELTA DE SATELITES´ DE LA V´IA LACTEA´ En este trabajo presento un estudio acerca de la historia de formaci´onestelar de galaxias del Grupo Local y su aplicaci´onpara el caso de la galaxia enana esferoidal, Carina. La primera secci´onde este trabajo presenta un cat´alogode alta precisi´onde sat´elitesdel Halo externo de la V´ıaL´actea. Este cat´alogova a proveer informaci´on muy importante acerca de los par´ametrosestructurales y poblaciones estelares de los sat´elitesde la V´ıaL´actea. Esta tesis tambi´enpresenta el estudio de estrellas azules rezagadas encontradas en sat´elitesde la V´ıa L´actea. Con esta informaci´onen mano derivamos una t´ecnica para discriminar entre el n´umerode estrellas azules rezagadas y el numero de estrel- las j´ovenes. Esta t´ecnicaayudar´asignificativamente a derivar fracciones de estrellas jovenes sin el sesgo que producen las azules rezagadas, al momento de derivar las his- torias de formaci´onestelar. Luego, presento nuestro m´etodo para derivar la historia de formacion estelar, llamado Talos. Esta rutina presenta varias ventajas con respecto a otras implementaciones, principalmente porque usa la informacion de todas las regiones del CMD, usa tambi´en la distribuci´onde metalicidad del sistema como input y por tanto no es necesario hacer suposiciones previas acerca de la relacion entre la metalicidad y la edad, y finalmente porque considera varias propiedades de los datos observados al momento de construir los modelos sint´eticos,y de esta forma estos modelos son directamente comparables con los datos. Finalmente presento mi implementaci´onde la rutina Talos para derivar la historia de formaci´onestelar espacialmente resuelta de la galaxia enana esferoidal Carina. Gracias a la alta calidad de los datos usados, las ventajas del m´etodo usado para derivar la historia de formaci´onestelar y la implementaci´onde nuestra t´ecnicapara disciminar entre estrellas azules rezagadas y estrellas j´ovenes, los resultados aqu´ıpresentados al- canzan una alt´ısimaprecisi´oncon respecto a trabajos previos. En este trabajo pudimos descifrar que la poblaci´onde estrellas j´ovenes com´unmente encontradas en Carina, son en realidad estrellas azules rezagadas que han sido mal clasificadas. A partir de los resultados obtenidos concluimos que la formaci´onestelar de Carina est´adominada por un proceso de evolucin interna, y no por la influencia de marea que le ejerce la V´ıa L´actea,como mayoritariamente se concluye acerca de esta galaxia. i SUMMARY OF THESIS FOR THE DEGREE OF DOCTOR OF PHYLOSOPHY IN ASTRONOMY SPATIALLY RESOLVED STAR FORMATION HISTORY OF MILKY WAY SATELLITES: THE CASE OF CARINA I present a complete study about the derivation of star formation histories of local dwarf galaxies and apply our method to the case of the Carina dSph galaxy. The first section of the work presents a high quality photometric catalogue of Milky Way satellites in the outer Halo. This catalogue will then provide important information about the structural properties and stellar populations of Milky Way satellites. At the same time, these results, once derived, will shed valuable information about structure assembly, dark matter properties, formation of the Milky Way, galaxy interaction, and conditions of the early Universe, all of which are closely related to the properties of the systems in the Local Group. This thesis also presents a study of blue straggler stars found in Milky Way satellites. With this information we derived fundamental properties about these type of stars in very low stellar density galaxies, an environment in which these stars had practically never been studied before. With this information, we derived a new technique for discriminating blue straggler counts and young star counts. This technique will help significantly to derive unbiased young star population fractions in the studies of star formation histories of dwarf galaxies. After that, I present the routine I used for deriving the star formation history of Carina dSph galaxy, which is based on the synthetic CMD method, and is called Talos. This routine presents several advantages with respect to other implementations, mainly becuase it uses as input the information from all the CMD regions, it uses independent metallicity measurements that enable us to avoid assuming an age-metalicity relation, and because it consideres several characteristics of the observations when constructing the synthetic models and in this way this models are directly comparable to the data. Finally I present my implementation of the Talos routine to derive the spatially resolved star formation history of the Carina dSph. Thanks to the high quality data, the state-of-the-art routine, and the new technique to discriminate between blue stragglers counts and young star counts, the results presented in here reach an unprecedented accuracy. In this study, we were able to derive that the young star population often found in Carina, are actually missclassified blue stragglers, and hence, there are only two episodes of star formation in Carina instead of three as it has been often claimed. With all this new information in hand, we concluded that the star formation of Carina is dominated by an internal evolution process as opposed to tidal influence from the Milky Way as is the current consensus. ii Acknowledgements The work of this thesis was founded by two different projects. The first one is CONICYT-PCHA/Doctorado Nacional/2010-21100133, and the second one is CONI- CYT Anillo project ACT-1122. I thank the founding from those project, that enable me to carry out my PhD program and the consequent thesis. I thank my advisor Ricardo Mu~nozfor his support throughout all the length of my PhD program, for all the scientific discussions, and for all the opportunities he provided for me to travel abroad and work in different Universities during my PhD program. I also thank the committee for helpful comments on my thesis text that significantly helped improve the final result. I thank the professors in charge of the astronomy courses I received during all these years, which significantly help me to form my current knowledge about a variety of topics in astronomy. I sincerely thank my family for being around me throughout my life, for their advices, support, and for letting me follow my vocation with nothing but support and effort from them. I thank also my school friends, Ignacio, Pablo, Diego, Sebasti´an,Roc´ıo, Natalia y Constanza, with which I keep close relations until these days. Sharing with them filled me with very valuable advices and experiences, and were a tremendous injection of energy was received by them each time things during the PhD became a little messy. I also thank Pedro, a close friend from my time at Beaucheff, and with which I share very valuable memories. I also thank my office mates during this six years, Andr´es,Sergio, Thomas, Juli´an,and Sebasti´an.Their company was very useful for astronomical discussions, general advices about the student life, and mostly to make every day at the University more pleasent and fun. Finally, I thank my girlfriend the most, Celia, the love of my life, who was also my office mate during my PhD program. She significantly helped me with the text and work of this thesis, along with almost every decision I have made regarding my astronomical carrer and most of all, for making me extremely happy day after day, and motivating me to keep with my best effort every day. iii Table of Contents 1 Introduction 1 2 Photometric Catalogue of Outer Milky Way Satellites 6 2.1 Introduction: Milky Way Satellites and the Local Group . 6 2.1.1 Early History and Definitions . 6 2.1.2 Connecting Dwarf Galaxies with Dark Matter Halos and the Missing Satellites Problem . 8 2.1.3 Scaling relations in dwarf galaxies and connection to formation mechanisms . 12 2.2 Complete Catalogue: General Remarks . 22 2.3 Southern Region Catalogue Construction . 23 2.3.1 Photometry: Instrumental magnitude determination . 23 2.3.2 Astrometry . 25 2.3.3 Magnitude calibration: Sloan filters magnitude determination . 27 2.3.4 Merging Individual Files into Final Files . 32 2.4 Catalogue final results example . 34 3 Blue stragglers in Outer Milky Way Satellitesy 46 3.1 Introduction . 46 3.2 Data and Blue Straggler Selection . 49 3.3 Results . 53 iv 3.3.1 Blue Straggler Specific Fractions . 53 3.3.2 Blue straggler/Young Stars Discrimination . 57 3.3.3 Radial Distribution Analysis . 62 3.4 Discussion . 63 3.4.1 Dwarf Galaxies . 63 3.4.2 Globular Clusters . 64 3.4.3 Discriminating between Blue Straggler Counts and Young Star Counts . 66 3.5 Conclusions . 67 4 Star Formation History of Milky Way Satellites 69 4.1 Definitions and Generalities of the Star Formation History . 69 4.2 The Synthetic CMD Method . 71 4.2.1 Our Application of the Synthetic CMD Method: Talos . 78 4.3 Star Formation History Measurements on Milky Way Satellites . 82 5 Spatially Resolved Star Formation History of the Carina dSph Galaxy 91 5.1 Introduction . 91 5.2 Data . 93 5.2.1 Photometry . 93 5.2.2 Spectroscopy . 94 5.3 Method for deriving the Star Formation History of Carina .