A Dissertation entitled High Mass X-ray Binaries in Nearby Star-forming Galaxies by Blagoy Rangelov Submitted to the Graduate Faculty as partial fulfillment of the requirements for the Doctor of Philosophy Degree in Physics Dr. Rupali Chandar, Committee Chair Dr. John-David Smith, Committee Member Dr. S. Thomas Megeath, Committee Member Dr. Scott Lee, Committee Member Dr. Andrea H. Prestwich, Committee Member Dr. Patricia R. Komuniecki, Dean College of Graduate Studies The University of Toledo August 2012 Copyright 2012, Blagoy Rangelov This document is copyrighted material. Under copyright law, no parts of this document may be reproduced without the expressed permission of the author. An Abstract of High Mass X-ray Binaries in Nearby Star-forming Galaxies by Blagoy Rangelov Submitted to the Graduate Faculty as partial fulfillment of the requirements for the Doctor of Philosophy Degree in Physics The University of Toledo August 2012 High Mass X-ray Binaries (HMXBs), in which a compact object, either black hole or neutron star, is accreting material from a young, massive donor star, often dominate the high-energy emission from nearby star-forming galaxies. These high mass pairs are believed to form in star clusters, where most massive star formation takes place, but to become displaced from their parent clusters either because they are dynamically ejected or because their parent cluster has dissolved. We have con- ducted a systematic study of the formation and evolution of bright HMXBs in eight nearby galaxies, by detecting HMXBs from their X-ray emission in Chandra X-ray Observatory observations, and identifying their parent clusters and donor stars in optical observations taken with the Hubble Space Telescope. We use the X-ray and optical properties of these systems to determine the ages of the binaries, whether the compact objects are black holes or neutron stars, and to constrain the masses of the donor stars. iii This dissertation is dedicated to Iva, whose unwavering support and inspiration have carried me through this journey. Acknowledgments This dissertation could not have been written without my advisor, Prof. Rupali Chandar, who guided me through my academic program at the University of Toledo. She never accepted less than my best efforts. Thank you. I also wish to express my gratitude to Dr. Andrea Prestwich for her tremendously helpful and invaluable assistance and support. I would also like to thank my other Ph.D. committee members: Prof. JD Smith, Prof. Tom Megeath, and Prof. Scott Lee. v Contents Abstract iii Acknowledgments v Contents vi List of Tables ix List of Figures x 1 Introduction 1 1.1 X-rayBinaries............................... 3 1.2 High Mass X-ray Binaries in Nearby Galaxies . 6 1.3 HighMassX-rayBinariesandStarClusters . 8 1.4 TwoofNASA’sGreatestObservatories . 10 1.4.1 The Hubble Space Telescope ................... 10 1.4.2 The Chandra X-ray Observatory ................. 12 1.5 DissertationOutline ........................... 12 2 The Connection Between X-ray Binaries and Star Clusters in NGC 4449 14 2.1 Introduction................................ 15 2.2 X-ray Observations from Chandra .................... 16 2.2.1 DataandReduction ....................... 18 vi 2.2.2 SourceDetectionandX-rayProperties . 18 2.2.3 X-rayColorsandModels. .. .. 22 2.3 Optical Observations from HST ..................... 25 2.3.1 DataandPhotometry ...................... 25 2.3.2 ColorMagnitudeDiagramofDonorStars . 27 2.3.3 Cluster Selection . 29 2.3.4 ClusterAge,MassandSizeEstimates. 29 2.4 Formation and Disruption of the Clusters . 33 2.5 Spatial Correlation Between X-ray and Optical Sources . .. 37 2.5.1 Correlation Between the Positions of XRBs and Star Clusters 37 2.5.2 Optical Sources That are Coincident With HMXBs . 40 2.6 Discussion................................. 41 2.6.1 PropertiesofStarClustersClosesttoHMXBs . 41 2.6.2 A Population of Very Young, Massive Black Hole Binaries in NGC4449............................. 43 2.6.3 Processes Responsible for the Spatial Displacement Between BHBsandStarClusters . .. .. 45 2.6.4 The Nature of Older X-ray Binaries in NGC 4449 . 47 2.7 SummaryandConclusions ........................ 49 3 X-ray Binaries and Star Clusters in the Antennae: Optical Cluster Counterparts 52 3.1 Introduction................................ 53 3.2 DataandSourceCatalogs ........................ 55 3.2.1 X-rayObservationsandCatalogofXRBs. 55 3.2.2 Optical Observations and Catalog of Star Clusters . 59 3.3 Astrometric Matching of the X-ray and Optical Catalogs . 60 vii 3.4 OpticalStarClusterCounterpartstoXRBs . 61 3.5 Discussion................................. 69 3.5.1 Constraining the Nature of XRBs within Star Clusters . 69 3.5.2 The Nature of HMXBs Associated with Star Clusters in the Antennae ............................. 70 3.6 SummaryandConclusions ........................ 72 4 High Mass X-ray Binaries in Nearby Starburst Galaxies 74 4.1 Introduction................................ 74 4.2 X-ray Observations from Chandra .................... 77 4.3 Identification ofOpticalCounterpartstoXRBs . 78 4.4 Results................................... 84 4.5 Discussion................................. 88 4.5.1 The Nature of the Ultra Luminous X-ray Source in Henize 2-10 88 4.5.2 X-rayColorsofXRBs ...................... 88 4.5.3 Correlation Between the Positions of XRBs and Star Clusters 90 4.5.4 CandidateDonorStars. .. .. 93 4.6 SummaryandConclusions ........................ 93 5 Summary and Future Prospects 95 References 98 viii List of Tables 2.1 Chandra Observations ............................ 20 2.2 X-raysourcecatalogue ............................ 21 2.3 Model parameters for X-ray sources with > 50counts........... 23 2.4 HST Images ................................. 26 2.5 Starclustercatalogue............................. 30 2.6 Properties of Star Cluster Closest to XRBs in NGC 4449 . 41 3.1 OpticalcounterpartstoX-raysources. ... 63 4.1 SampleGalaxies ............................... 77 4.2 Chandra Observations ............................ 78 4.3 CatalogueoftheXRBCandidates. 79 4.4 CloseststarclusterstoXRBs . .. .. 81 4.5 DonorstarsofXRBs ............................. 83 ix List of Figures 1-1 Artist’sconceptionofanX-raybinary . 2 1-2 Accretionontoacompactobject . 4 1-3 Canonical spectral states of BHX-ray binaries . .... 7 1-4 OpticalandX-rayimagesofM101 . 9 1-5 PredictednumberofHMXBs . .. .. 11 2-1 ColorimageofNGC4449 .......................... 17 2-2 Locations of star cluster and X-ray sources on the V band HST image . 19 2-3 X-ray color-color diagram of X-ray binaries in NGC 4449 . .. 24 2-4 Color magnitude diagram of optical point sources . .. 28 2-5 Optical two-color diagrams of all star clusters . ... 31 2-6 Mass-agediagramofallclusters . 34 2-7 Age distribution of clusters in NGC 4449 . 35 2-8 Cumulative distribution of the displacement between X-ray binaries and starclusters.................................. 38 2-9 Same as Figure 2-8, but excluding all BHBs and the known LMXB . 50 3-1 OpticalimageoftheAntennaegalaxies . 57 3-2 The locations of the 22 XRBs that are coincident with a star cluster... 58 3-3 A2.5′′ × 2.5′′ region around each of the 22 coincident sources . 66 4-1 HST imagesofthesixstarburstgalaxies . 76 4-2 X-ray color-color diagram of X-ray binaries in nearby starburst galaxies . 85 x 4-3 Cumulative distribution of the displacement between X-ray binaries and star clusters in six starburst and Antennae galaxies . 86 4-4 Color magnitude diagram of optical point sources in six starburst galaxies 87 4-5 Retained and ejected from star clusters BH and NS . ... 91 xi Chapter 1 Introduction A major goal of astronomy in the last century has been to understand the broad sweep of stellar evolution. How do stars form and evolve? Our understanding of stellar evolution has come a long way from Hertzsprung-Russell diagrams to detailed population synthesis models. We now know that molecular clouds form thousands of protostars which then spend the majority of their lives on the main sequence before evolving into giants or supergiants, and after spectacular deaths, end their lives as compact objects − white dwarfs (WDs), neutron stars (NSs), or black holes (BHs). White dwarfs are the final evolutionary state of all stars whose initial masses do not exceed ∼ 8 M⊙. The remnants of main sequence stars with higher mass are NSs or BHs, depending on how much mass is left in their cores at the end of their main sequence (nuclear burning) lifetime (Heger et al. 2003). White dwarfs are compact < objects with masses ∼ 1.4 M⊙, the so-called Chandrasekhar limit (Chandrasekhar 1931). In stars that have core masses that exceed this limit at the end of their main sequence lives, the atoms are crushed, and the electrons and the protons fuse together to form an object composed almost entirely of neutrons − neutron stars. If the mass of the stellar remnant is more than ∼ 3 M⊙, neutron degeneracy pressure cannot halt the gravitational collapse, and the object will form a black hole. In this dissertation we will focus on NSs and BHs. 1 Figure 1-1 Artist’s conception of an X-ray binary. Compact object is accreting mass from companion star. The massive disk formed around the compact object is heated to such high temperatures that X-rays are emitted. (Credit: NASA/CXC). Over the last several decades, observing the universe at different wavelengths led to the discovery of previously unknown classes of objects. X-ray binaries (XRBs), for example, were an important and unexpected discovery. Shortly after the launch of the