[Normal Galaxies, Clusters of Galaxies -- Oral ]

X-ray source populations in nearby spiral and star-forming galaxies

Andreas Zezas, Harvard-Smithsonian Center for Astrophysics, University of Crete (Greece)
V. Antoniou (CfA), K. Gazeas (CfA), P. Sell (U. Wisconsin), G. Fabbiano (CfA), V. Kalogera (Northwestern U.), D. Pooley (U. Wisconsin)

We present results on the X-ray source populations of nearby spiral and star-forming galaxies. The sample of galaxies includes the nearby spiral galaxy M81 and star-forming galaxies with stellar populations in the 10-100Myr range. We use HST data in order to classify the X-ray sources to HMXBs, LMXBs and globular clusters, and identify any SNRs or background AGNs. We discuss the spectral and temporal characteristics of the different sub-populations in these galaxies, and their implications for the sources' nature. We present the X-ray luminosity functions (XLF) of the discrete sources from the individual as well as the co-added observations and we discuss the dependence of the XLF on the age of the stellar populations. In the case of M81 we find a population of sources in the $10\^{36}-10\^{37}\rm{erg s\^{-1}}$ luminosity range with early-type counterparts, while the HMXBs in the star-forming galaxies have generally higher luminosities. We also present results from Chandra observations of the SMC which extend the XLFs down to luminosities of $10\^32\rm{erg s\^{-1}}$ and show evidence for the onset of the propeller effect at low luminosities.