X-ray Binaries in Nearby Galaxies Vicky Kalogera Northwestern University • Super Star Clusters • Starburst galaxies • Ultra-Luminous X-Ray Sources • Elliptical galaxies
Jan 21, 2016
X-ray Binaries in Nearby Galaxies
Vicky Kalogera Northwestern University
• 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 star-formation history and metallicity ?
Do Super Star Clusters form High-Mass XRBs ?
What determines the shape of 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) ?
Super-Star Clusters (SSCs)
• Compact, young analog to globular clusters• Found frequently in starburst environments
• Masses range from ~104 to ~106 M
•Ages range from a few to tens of Myr
Kaaret et al. 2004
• Lx ≥ (0.5-3)x1036 erg/s
Distribution of X-Ray point sources
< 1 XRB per cluster!
Kaaret et al. 2004
• Lx ≥ 5x1035 erg/s
Distribution of X-Ray point sources
• XRBs closely associated with star clusters• Median distance ~30-100 pc
< 1 XRB per cluster!M82N5253
N1569
50%
Is this all due to Is this all due to Supernova Kicks ?Supernova Kicks ?
Theoretical XRB Distributions
• cluster mass: ~5x104 Mo
• LX > 5x1035 erg/s• average of 1,000 cluster simulations
• Significant age dependence
• < 1 XRB per cluster
Models: Population Syntheses of XRBs and Kinematic Orbit Evolution in Cluster Potential
Sepinsky et al. 2005, ApJL
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
• 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
Supernova kicks: eject XRBs @ D > 10pc especially for M < 105 Mo
NGC 1569NGC 1569(post-)starburst galaxy at 2.2Mpcwith well-constrained SF history: > ~100Myr-long episode, probably ended 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
Vallenari & Bomans 1996;Greggio et al. 1998;Aloisi et al. 2001; Martin et al. 2002
courtesySchirmer, HST
courtesyMartin, CXC,NOAO
Belczynski, VKet al. 2004, ApJL
NGC 1569 XLF modeling
Hybrid of 2 populations:
underlying old starburst young
Old: 1.5 GyrYoung: 110 MyrSFR Y/O: 20
Old: 1.5 GyrYoung: 70 MyrSFR Y/O: 20
Old: 1.3 GyrYoung: 70 MyrSFR Y/O: 40
Conclusions on Starbursts
Current understanding of XRB formation and evolution produces XLF properties consistent with observations Model XLFs can be used to constrain star-formation properties, e.g., age and metallicity
Shape of model XLFs appear robust against variations of most binary evolution parameters
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 ?
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
IMBH Companions
Mass Mass distributiondistribution
Orbital separation Orbital separation distributiondistribution
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
Brightest XRBs in Elliptical Galaxies
Upper-end XLF slope (LX: from ~0.5 - 2 1039 erg/s) :
footprint of accreting BH mass spectrummodified by probability of XRB detection due to
transient mode of accretion
Ivanova & VK 2005, ApJ
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 rarebrightest sources and questions of BH formation
* Systematic modeling of galaxy samples will reveal sensitivity to SFR and Z …