Astrophys. J., 602, 231-248 (2004/February-2)
Old and young X-ray point source populations in nearby galaxies.
COLBERT E.J.M., HECKMAN T.M., PTAK A.F., STRICKLAND D.K. and WEAVER K.A.
Abstract (from CDS):
We have analyzed Chandra ACIS observations of 32 nearby spiral and elliptical galaxies and present the results of 1441 X-ray point sources that were detected in these galaxies. The total point-source X-ray (0.3-8.0 keV) luminosity LXPis well correlated with the B-band, K-band, and FIR+UV luminosities of spiral host galaxies and is well correlated with the B-band and K-band luminosities of elliptical galaxies. This suggests an intimate connection between LXPand both the old and young stellar populations, for which K and FIR+UV luminosities are reasonable proxies for the galaxy mass M and star formation rate SFR. We derive proportionality constants α=1.3x1029 ergs/s/M☉ and β=0.7x1039 ergs/s (M☉/yr)–1, which can be used to estimate the old and young components from M and SFR, respectively. The cumulative X-ray luminosity functions for the point sources have significantly different slopes. For the spiral and starburst galaxies, γ~0.6-0.8, and for the elliptical galaxies, γ~1.4. This implies that the most luminous point sources–those withLX≳1038ergs/s–dominateLXPfor the spiral and starburst galaxies. Most of the point sources have X-ray colors that are consistent with soft-spectrum (photon index Γ∼1-2) low-mass X-ray binaries, accretion-powered black hole high-mass X-ray binaries (BH HMXBs), or ultraluminous X-ray sources (ULXs, also known as IXOs). We rule out hard-spectrum neutron star HMXBs (e.g., accretion-powered X-ray pulsars) as contributing much to LXP. Thus, for spirals, LXPis dominated by ULXs and BH HMXBs. We find no discernible difference between the X-ray colors of ULXs (LX≥1039 ergs/s) in spiral galaxies and point sources with LX~1038-1039 ergs/s. We estimate that ≳20% of all ULXs found in spirals originate from the older (Population II) stellar populations, indicating that many of the ULXs that have been found in spiral galaxies are in fact Population II ULXs, like those in elliptical galaxies. We find that LXPdepends linearly (within uncertainties) on both M and SFR for our sample galaxies (M≲1011 M☉and SFR≲10 M☉/yr).
X-Rays: Binaries - X-Rays: Galaxies
VizieR on-line data:
<Available at CDS (J/ApJ/602/231): table1.dat table2.dat tablea1.dat>
Table A1: [CHP2004] JHHMMSS.s+DDMMSS N=1441.
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