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[46.02] Young and Old X-ray Binary and IXO Populations in Spiral and Elliptical Galaxies

E. Colbert, T. Heckman, A. Ptak, D. Strickland (JHU), K. Weaver (NASA/GSFC)

We have analyzed Chandra ACIS observations of 32 nearby spiral and elliptical galaxies and present the results of 1441 X-ray point sources, which are presumed to be mostly X-ray binaries (XRBs) and Intermediate-luminosity X-ray Objects (IXOs, a.k.a. ULXs). The X-ray luminosity functions (XLFs) of the point sources show that the slope of the elliptical galaxy XLFs are significantly steeper than the spiral galaxy XLFs, indicating grossly different types of point sources, or different stages in their evolution. Since the spiral galaxy XLF is so shallow, the most luminous points sources (usually the IXOs) dominate the total X-ray point source luminosity L_XP. We show that the galaxy total B-band and K-band light (proxies for the stellar mass) are well correlated with L_XP for both spirals and ellipticals, but the FIR and UV emission is only correlated for the spirals. We deconvolve L_XP into two components, one that is proportional to the galaxy stellar mass (pop II), and another that is proportional to the galaxy SFR (pop I). We also note that IXOs (and nearly all of the other point sources) in both spirals and ellipticals have X-ray colors that are most consistent with power-law slopes of Gamma ~ 1.5--3.0, which is inconsistent with high-mass XRBS (HMXBs). Thus, HMXBs are not important contributors to L_XP. We have also found that IXOs in spiral galaxies may have a slightly harder X-ray spectrum than those in elliptical galaxies. The implications of these findings will be discussed.

Bulletin of the American Astronomical Society, 35#2
© 2003. The American Astronomical Soceity.