X-RAY SCALING LAWS for GALAXY CLUSTERS and GROUPS By
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X-RAY SCALING LAWS FOR GALAXY CLUSTERS AND GROUPS by Donald J. Horner Dissertation submitted to the Faculty of the Graduate School of the University of Maryland, College Park in partial fulfillment of the requirements for the degree of Doctor of Philosophy 2001 Advisory Committee: Professor Richard F. Mushotzky, Advisor Professor Andrew S. Wilson, Chairman Professor Sylvain Veilleux Professor M. Coleman Miller Professor Theodore Jacobson Professor Craig L. Sarazin ABSTRACT Title of Dissertation: X-RAY SCALING LAWS FOR GALAXY CLUSTERS AND GROUPS Donald J. Horner, Doctor of Philosophy, 2001 Dissertation directed by: Professor Richard F. Mushotzky Department of Astronomy Scaling laws between galaxy cluster properties, such as the x-ray luminosity{ temperature relation (L{T), the total mass-temperature relation (M{T), and ve- locity dispersion { temperature relation (σ{T) reflect the underlying physics in cluster formation and evolution. The differences between empirically determined and theoretically predicted scaling laws can give useful insights into physical pro- cesses happening in clusters. To determine these scaling laws, we have developed a data reduction pipeline for clusters observed by the ASCA x-ray satellite to cre- ate a sample of 273 clusters and groups with measured x-ray luminosities, average temperatures, and metal abundances. This is the largest such sample yet created and will form a baseline for future studies with improved instruments like Chandra and XMM-Newton. We compare our ASCA cluster catalog to data in the literature to examine some of the biases and systematics that affect measurement of x-ray properties, and illuminate issues that affect the science results derived from such x-ray samples. We derive the L{T relationship over several orders of magnitude in luminosity, from rich clusters to groups. In combination with data from the literature, we examine the M-T relationship for a variety of mass estimators. We then examine the σ{ T relationship and other correlations between the optical and x-ray properties of galaxy clusters. In general, we find that these scaling laws are affected by non- gravitational processes which require additional physics, e.g., energy injection by supernovae. We also see little evolution of galaxy cluster properties with redshift to z ∼ 0:5. c Copyright by Donald J. Horner 2001 Preface This thesis was written under the supervision of Dr. Richard Mushotzky at the Laboratory for High Energy Astrophysics (LHEA) at Goddard Space Flight Cen- ter (GSFC). It is divided into nine chapters and two appendices. The figures in Chapter 2, which reviews x-ray instrumentation and data analysis, are nearly all taken from Appendix E of the ASCA Technical Description. The remaining fig- ures in the chapter were taken from the web site of the High Energy Astrophysics Science Archive Research Center (HEASARC). The initial version of the ASCA cluster catalog described in Chapter 3 was created by Dr. Keith Gendreau. Using this as a basis, I rewrote and improved the reduction and analysis routines to the present version described in Chapter 3. Except for parts of Chapter 7 which were previously published as Horner et al. (1999) in collaboration with Dr. Mushotzky and Dr. Caleb Scharf, the rest of the thesis is original work. This thesis has also utilized a number of on-line resources, including data obtained from the High Energy Astrophysics Science Archive Research Center (HEASARC), the NASA/IPAC Extragalactic Database (NED), and NASA's Astrophysics Data System (ADS) Abstract Service. ii DEDICATION To Yanga Rolando Fern´andez-Ponte Martin, who sent me the most postcards. iii ACKNOWLEDGEMENTS I would like to thank my advisor, Richard Mushotzky, for his advice, ideas, and patience. I also need to thank my thesis committee and all the people who read earlier versions of this thesis. It was greatly improved by their comments. At Goddard, I would like to thank Keith Arnaud, Keith Gendreau, and Koji Mukai for answering my many ques- tions about x-ray astronomy, data reduction, and analysis. I also have to thank the WARPS team for giving me the opportunity to become involved in the project, with a special thanks to Caleb Scharf who helped usher me through the early days of my research work. At the University of Maryland, I have to thank John Trasco and Mary Ann Phillips for helping me navigate through the dangerous water of the University and departmental administration. On a more personal note, I would also like to thank my office mates past and present, especially Wayne Baumgartner. I also need to thank Craig Markwardt, not only for his IDL expertise, but also for his sarcasm and Tali Figueroa for also writing his thesis at the same time. It helped to have someone else around dealing with similar pressures. I also thank Steve Fantasia and Mike Arida for not throwing me out when I stopped by their offices for no good reason and for keeping me with candy and gum. A special thanks to everyone in T{Club for the entertainment and cookies over the years, although this is somewhat offset by the repeated mocking. And to Maggie Masetti, I'm sorry you got fired. I would also like to thank fellow (former) graduate students Yan Fer- nandez and Laura Woodney for all the postcards they sent me (not to mention the love and support and all that stuff) and making grad school bearable. Even though they didn't send me as many postcards, I would like to thank Kip Kuntz, Leslie Looney, Arunav Kundu, Neil Nagar, Scott Miller and (most) of the rest of the grad students for their iv friendship. I also thank everyone else who sent me a postcard, espe- cially Barb Mattson, who is truly insane. I also have to mention Robert Greundl, Phil Esterle, and Jim Braatz for helping me get through the first few years of grad school. v TABLE OF CONTENTS List of Tables x List of Figures xi 1 Introduction 1 1.1 Optical Observations . 3 1.1.1 Catalogs . 3 1.1.2 Morphology and Spatial Distribution . 4 1.1.3 Luminosity Function of Galaxies . 5 1.1.4 Velocity Distribution of Galaxies . 5 1.1.5 Galactic Content of Clusters . 6 1.2 X-ray Observations . 7 1.2.1 Catalogs . 7 1.2.2 The X-ray Spectrum from Hot Plasma . 8 1.2.3 Spatial Distribution of the Gas . 10 1.2.4 Mass Estimates . 10 1.2.5 Cooling Flows . 11 2 X-ray Instrumentation and Data Analysis 13 2.1 The ASCA Satellite . 13 2.1.1 The X-ray Telescope . 14 2.1.2 The SIS . 15 2.1.3 The GIS . 17 2.1.4 Processing of ASCA data . 18 2.2 Other X-ray Astrophysical Missions . 19 2.3 The Basics of Spectral Fitting . 20 3 The ASCA Cluster Catalog 22 3.1 Introduction . 22 3.2 Constructing the Cluster Sample . 23 3.3 Extraction Region Selection . 26 vi 3.4 Reduction of the GIS Data . 28 3.5 Reduction of the SIS Data . 29 3.6 Combining Spectrum Files . 29 3.7 Spectral Fitting . 29 3.8 Luminosity Correction . 30 3.9 Consistency Checks . 32 3.9.1 Multiple Observations . 32 3.9.2 GIS versus SIS . 33 3.9.3 MEKAL versus Raymond-Smith models . 33 3.10 Conclusions . 36 4 Comparison to Other Catalogs 39 4.1 X-ray Temperature . 39 4.1.1 Previous ASCA Results . 39 4.1.2 Non-ASCA Temperatures . 44 4.1.3 Groups . 46 4.2 Metal Abundance . 48 4.2.1 Previous ASCA Results . 48 4.2.2 Non-ASCA Abundances . 50 4.2.3 Groups . 51 4.3 Bolometric Luminosity . 53 4.3.1 Clusters . 53 4.3.2 Groups . 56 4.4 Conclusions . 57 5 Luminosity { Temperature Relation 58 5.1 Introduction . 58 5.2 Theory . 59 5.3 Observations . 60 5.4 The Slope of the Lx − Tx Relation . 61 5.5 Dispersion in the Lx − Tx Relationship . 65 5.5.1 Cooling Flows . 65 5.5.2 Metal Abundance . 69 5.5.3 Central Density . 71 5.5.4 Spatial Distribution . 71 5.6 Redshift Evolution . 73 5.7 Discussion and Conclusions . 74 vii 6 Metal Abundance 78 6.1 Introduction . 78 6.2 Abundance { Temperature Correlation . 79 6.3 Cooling Flows . 81 6.4 Central Density and Core Radius . 84 6.5 Evolution . 84 6.6 Discussion and Conclusions . 86 7 Mass { Temperature Relation 89 7.1 Introduction . 89 7.2 Theory and Simulations . 91 7.3 Virial Theorem Mass Estimates . 92 7.3.1 Scatter in Virial Mass Estimator . 94 7.4 X-ray Mass Estimates . 96 7.4.1 Mass Estimates with Spatially Resolved Temperature Profiles 96 7.4.2 The Isothermal β-model . 98 7.4.3 Surface Brightness Deprojection . 101 7.5 Updated Results . 103 7.5.1 Virial Theorem Mass Estimates . 103 7.5.2 The Isothermal β-model . 104 7.5.3 Mass Estimates with Spatially Resolved Temperature Profiles 104 7.6 Conclusions . 105 8 Optical to X-ray Scaling Laws 107 8.1 Introduction . 107 8.2 Optical Velocity Dispersion . 107 8.2.1 The Velocity Dispersion { Temperature Relation . 109 8.2.2 The Velocity Dispersion { X-ray Luminosity Relation . 110 8.3 Optical Luminosity . 111 8.4 Optical Richness . 114 8.4.1 Abell Richness . 115 8.4.2 Bahcall Richness . 119 8.4.3 Two Point Correlation Function . 119 8.5 Conclusions . 121 9 Summary and Conclusions 123 9.1 Summary of Data Reduction and Analysis . 123 9.2 Summary of Science Results . 124 9.3 Discussion . 126 Appendix 128 viii A Data Tables 128 A.1 Clusters Not Included in the ASCA Sample .