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A Unified Formation Scenario for the Zoo of Extended Star Clustersand Ultra-Compact Dwarf Galaxies

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A UNIFIED FORMATION SCENARIO FOR THE ZOO OF EXTENDED STAR CLUSTERS AND ULTRA-COMPACT DWARF GALAXIES DISSERTATION zur Erlangung des Doktorgrades (Dr. rer. nat.) der Mathematisch-Naturwissenschaftlichen Fakultät der Rheinischen Friedrich-Wilhelms-Universität Bonn vorgelegt von RENATE CLAUDIA BRÜNS aus Bonn Bonn, 2013 Angefertigt mit Genehmigung der Mathematisch-Naturwissenschaftlichen Fakultät der Rheinischen Friedrich-Wilhelms-Universität Bonn 1. Gutachter: Prof. Dr. P. Kroupa 2. Gutachter: Prof. Dr. U. Klein Tag der Promotion: 16. Juni 2014 Erscheinungsjahr: 2014 Contents Abstract 1 1 Introduction 3 1.1 Old Star Clusters in the Local Group ......................... 3 1.2 Old Star Clusters beyond the Local Group ..................... 7 1.3 Ultra-Compact Dwarf Galaxies ............................ 8 1.4 Young Massive Star Clusters and Star Cluster Complexes ............. 9 1.5 Outline of Thesis .................................... 14 2 NumericalMethod 17 2.1 N-BodyCodes ..................................... 17 2.1.1 Set-Up of the Initial Conditions ....................... 18 2.1.2 The Integrator ................................. 22 2.1.3 Determination of Accelerations from the N Particles ............ 23 2.1.4 The Analytical External Tidal Field ..................... 26 2.1.5 Determination of the Enclosed Mass and the Effective Radius ...... 29 2.2 The Particle-Mesh Code SUPERBOX ......................... 29 2.2.1 Definition of the Grids and the Determination of Accelerations ...... 30 2.2.2 Illustration of the Combination of the Grid Potentials ........... 32 2.2.3 General Framework for the Choice of Parameters for the Simulations . 34 2.2.4 SUPERBOX++ versus Fortran SUPERBOX ................... 40 3 ACatalogofECsandUCDsinVariousEnvironments 43 3.1 Introduction ...................................... 43 3.2 The Observational Basis of the EO Catalog ..................... 44 3.2.1 EOs in Late-Type Galaxies .......................... 44 3.2.2 EOs in Early-Type Galaxies .......................... 44 3.3 Results ......................................... 45 3.3.1 Trends and Correlations of the EO Parameters ............... 45 3.3.2 Correlation of EO Parameters with those of their Host Galaxies. ..... 48 3.4 Discussion ....................................... 49 3.4.1 Distribution in the Effective Radius Versus Total Luminosity Space ... 49 3.4.2 EO Luminosity Functions ........................... 55 3.4.3 Spatial Distribution of EOs .......................... 60 3.5 Summary & Conclusions ............................... 63 I II CONTENTS 4 AnApplicationoftheFormationScenarioonSpecificEOs 65 4.1 Introduction ...................................... 65 4.2 Faint Fuzzy Star Clusters in NGC 1023 ....................... 66 4.2.1 Introduction .................................. 66 4.2.2 Set-up of the Numericial Simulations and Varied Parameters ....... 67 4.2.3 Results ..................................... 69 4.2.4 Discussion and Conclusions ......................... 74 4.3 The Milky Way EO NGC 2419 ............................ 78 4.3.1 Introduction .................................. 78 4.3.2 Set-Up and Varied Parameters ........................ 79 4.3.3 Results ..................................... 84 4.3.4 Discussion ................................... 93 4.3.5 Summary .................................... 96 4.4 Conclusions ...................................... 97 5 AGeneralStudyontheFormationofECsandUCDs 99 5.1 Introduction and General Set-Up ........................... 99 5.2 The Effect of the Initial CC Parameters Mass and Size ............... 102 5.2.1 Numerical Set-Up and Varied Parameters .................. 102 5.2.2 Results ..................................... 103 5.2.3 Comparison with Observations ....................... 111 5.3 The Influence of the Orbit on the Evolution of Merger Objects .......... 112 5.3.1 Numerical Set-Up and Varied Parameters .................. 112 5.3.2 Results from the Circular Orbits ....................... 113 5.3.3 Results from the Eccentric Orbits ...................... 120 5.3.4 Comparison with Observations ....................... 124 5.4 The Formation of Extremely Extended Clusters ................... 125 5.4.1 Numerical Set-Up and Varied Parameters .................. 126 5.4.2 Results ..................................... 126 5.4.3 Comparison with Observations ....................... 128 5.5 Discussion ....................................... 129 5.5.1 The Merging Star Cluster vs. the Galaxy Threshing Scenario ....... 129 5.5.2 The Gilmore Gap ............................... 132 5.6 Conclusion ....................................... 135 6 Summary 137 6.1 A Comprehensive Catalog of Observed EOs .................... 138 6.2 The Application of the Formation Scenario to Specific EOs ............ 138 6.2.1 Faint Fuzzy Star Clusters in NGC 1023 ................... 138 6.2.2 The Milky Way Cluster NGC 2419 ...................... 139 6.3 A General Study on the Formation of EOs ...................... 140 6.3.1 A Parameter Study of the Initial CC Parameters Mass and Size ...... 140 6.3.2 A Parameter Study of the Dependence on the Orbit ............ 140 6.3.3 A Parameter Study on the Formation of Extremely Extended EOs .... 141 6.4 Conclusion ....................................... 141 7 Outlook 143 7.1 Observational Constraints on the Initial CCs .................... 143 7.2 Computational Refinements of the Merging Star Cluster Scenario ........ 144 7.3 Computational Projects for the Galaxy Threshing Scenario ............ 146 CONTENTS III 7.4 Observational Requirements on EOs ......................... 146 A Catalog of Extended Stellar Dynamical Objects 149 B AManualforMergingStarClusterSimulations 169 B.1 Setup of a Cluster Complex on an Orbit Around a Galaxy ............. 169 B.1.1 Creation of a Star Cluster ........................... 169 B.1.2 Generation of a Cluster Complex Model .................. 173 B.1.3 Concatenation of the CC Distribution, the Individual SCs, and the Orbit 173 B.2 Running the Simulations ............................... 174 B.2.1 Determination of Merged Star Clusters ................... 176 C Summary Tables of the Simulation Results 181 C.1 Results of the Study of Faint Fuzzies in NGC 1023 ................. 182 C.2 Results of the Study of the Milky Way EO NGC 2419 ................ 183 C.3 Nomenclature of the Simulations of the General EO Study ............ 184 C.4 Results of the Study with Varied Initial CC Parameters Mass and Size ...... 185 C.5 Results of the Study with Varied Orbital Parameters ................ 187 C.6 Results of the Study on the Formation of Extremely Extended EOs ........ 188 Bibliography 189 Acknowledgements 199 IV CONTENTS List of Figures 1.1 Effective radii vs. distances of GCs/ECs of the Milky Way and its companions . 4 1.2 Effective radii vs. luminosities of GCs/ECs of the Milky Way and its companions 5 1.3 The Antennae galaxies and the exemplary CC knot S ............... 10 1.4 The Whirlpool galaxy and an exemplary CC in the galactic disk ......... 12 1.5 The Tadpole galaxy and an exemplary CC in the tidal tail ............. 13 2.1 Basic structure of an N-body code .......................... 18 2.2 Illustration of the leapfrog integrator ........................ 22 2.3 Geometry of the determination of the effective potential .............. 27 2.4 Illustration of the impact of the mass and size of a CC on its tidal radius ..... 28 2.5 Determination of the enclosed mass and effective radius of a merger object ... 29 2.6 Illustration of the three different grids used in SUPERBOX ............. 31 2.7 Illustration of the different combinations of the grid potentials .......... 31 2.8 Example of the determination of the total potential ................. 33 2.9 Illustration of the setup of the merging star cluster simulations .......... 35 2.10 Surface density profile of a merger object for different grid resolutions ...... 36 2.11 Surface density profile of a merger object for different numbers of particles ... 38 2.12 Illustration of the merging criterion ......................... 39 2.13 Comparison of results from SUPERBOX and SUPERBOX++ ............. 41 3.1 Effective radii of EOs versus their total V-band luminosities ............ 45 3.2 Effective radii and total luminosities of EOs vs. their projected distances .... 46 3.3 Histogram of the number of EOs at different total V-band luminosities ..... 47 3.4 Histogram of the number of EOs at different effective radii ............ 47 3.5 Histogram of the number of EOs at different projected radii ............ 47 3.6 EO parameters vs. the total V-band luminosity of their host galaxy ........ 49 3.7 EO parameters vs. distance of their host galaxy to the Galaxy ........... 50 3.8 EO parameters and trends of equal mean surface brightness ........... 51 3.9 Overview of confirmed and candidate EOs ..................... 52 3.10 Observed parameters of GCs, EOs, and early-type galaxies ............ 53 3.11 Histogram of the effective radii of all GCs and EOs ................ 54 3.12 Luminosity function of EOs in late-type galaxies .................. 55 3.13 Luminosity function of EOs in NGC 4365 ...................... 56 3.14 Luminosity function of EOs in early-type galaxies ................. 57 3.15 Luminosity function of EOs in early-type galaxies w/o NGC 4365 and NGC 1275 57 3.16 Turnover of the luminosity function as a function of the effective radius ..... 59 3.17 Overview of the distribution of EOs in M51 ..................... 61 3.18 Spectroscopically confirmed star clusters of the Hydra Cluster .......... 62 V VI LIST OF
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