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X-ray Binaries in Nearby Galaxies

Vicky Kalogera Northwestern University. X-ray Binaries in Nearby Galaxies. Super Star Clusters Starburst galaxies Ultra-Luminous X-Ray Sources Elliptical galaxies. Chandra observations of XRBs - some of the puzzles -. How does XRB formation and evolution depend on

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X-ray Binaries in Nearby Galaxies

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  1. Vicky Kalogera Northwestern University X-ray Binaries in Nearby Galaxies • Super Star Clusters • Starburst galaxies • Ultra-Luminous X-Ray Sources • Elliptical galaxies

  2. Chandra observations of XRBs - some of the puzzles - How does XRB formation and evolution depend on star-formation history and metallicity ? Do Super Star Clusters form High-Mass XRBs ? Whatdeterminestheshapeof X-Ray Luminosity Functions (XLF) ? Is it due to a blend of different XRB populations ? What is the nature of Ultra-Luminous X-ray Sources (ULX) ?

  3. Super-Star Clusters (SSCs) • Compact, young analog to globular clusters • Found frequently in starburst environments • Masses range from ~104 to ~106 Mo • Ages range from a few to tens of Myr

  4. Distribution of X-Ray point sources Kaaret et al. 2004 • Lx≥ (0.5-3)x1036 erg/s < 1 XRB per cluster!

  5. N1569 50% N5253 M82 Distribution of X-Ray point sources • XRBs closely associated with star clusters • Median distance ~30-100 pc Kaaret et al. 2004 Is this all due to Supernova Kicks ? • Lx≥ 5x1035 erg/s < 1 XRB per cluster!

  6. Theoretical XRB Distributions Sepinsky et al. 2005, ApJL Models: Population Syntheses of XRBs and Kinematic Orbit Evolution in Cluster Potential • cluster mass: ~5x104 Mo • LX > 5x1035 erg/s • average of 1,000 cluster simulations • Significant age dependence • < 1 XRB per cluster

  7. Conclusions XRB models without cluster dynamics appear in agreement with observations • Mean XRB number per SSC < 1 and spatial distribution: M < 105 Mo and 10-50Myr or more massive and ~50Myr • Supernova kicks: eject XRBs @ D > 10pc especially for M < 105 Mo • Results do not appear sensitive to binary evolution assumptions, but extended parameter study is needed. • Explore role of dynamics for more massive and older clusters

  8. NGC 1569 (post-)starburst galaxy at 2.2Mpc with well-constrained SF history: > ~100Myr-long episode, probablyended 5-10Myr ago,Z ~ 0.25 Zo >older population with continuous SF for ~ 1.5Gyr, Z ~ 0.004 or 0.0004, but weaker in SFR than recent episode by factors of >10 courtesy Schirmer, HST courtesy Martin, CXC,NOAO Vallenari & Bomans 1996; Greggio et al. 1998; Aloisi et al. 2001; Martin et al. 2002

  9. Old: 1.3 Gyr Young: 70 Myr SFR Y/O: 40 Old: 1.5 Gyr Young: 110 Myr SFR Y/O: 20 NGC 1569 XLF modeling Belczynski, VK et al. 2004, ApJL Old: 1.5 Gyr Young: 70 Myr SFR Y/O: 20 • Hybrid of • 2 populations: • underlying old • starburst young

  10. Current understanding of XRB formation and evolution produces XLF properties consistent with observations Model XLFs can be used to constrainstar-formation properties, e.g., age and metallicity Shape of model XLFs appear robust against variations of most binary evolution parameters Conclusions on Starbursts

  11. Ultra-Luminous X-ray Sources • First discovered with Einstein X-ray telescope • Extragalactic sources with LX≥ 1039 erg/s • Later observations determined many are off-nuclear & not associated with supernovae • What is the origin of these sources? • Intermediate-Mass Black Holes? (50 - 1000Mo) • Strongly Anisotropic XRB emission ?

  12. IMBH Binaries ? Cluster core simulations with binary evolution and multi-body dynamical interactions Do IMBH acquire mass-transfering binary companions in cluster cores ? Blecha, Ivanova, VK et al. 2005

  13. IMBH Companions Mass distribution Orbital separation distribution

  14. Conclusions on IMBH Binaries • Optimal IMBH mass range: 100-200 Mo • MT is relatively rare; highest incidence at 100Mo about 3-5% of cluster lifetime with MT IMBH binary • MS mass-transferring companions are more common & spend more time in MT BUT ARE THEY ULXs? Blecha, Ivanova, VK et al. 2005

  15. Brightest XRBs in Elliptical Galaxies Upper-end XLF slope (LX: from ~0.5 - 2 1039 erg/s) : footprint of accreting BH mass spectrum modified by probability of XRB detection due to transient mode of accretion Ivanova & VK 2005, ApJ

  16. What to Expect in the Future ? • For example: • Long-term time monitoring will become possible; • identification of X-ray transients • and clues to ULX nature • Bigger source samples will allow probing the rare • brightest sources and questions of BH formation • Systematic modeling of galaxy samples will • reveal sensitivity to SFR and Z …

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