LOW-MASS X-RAY BINARIES AND GLOBULAR CLUSTERS IN EARLY-TYPE GALAXIES. I. CHANDRA OBSERVATIONS

We present a Chandra survey of LMXBs in 24 early-type galaxies. Correcting for detection incompleteness, the X-ray luminosity function (XLF) of each galaxy is consistent with a power law with negative logarithmic differential slope, beta similar to 2.0 However, beta strongly correlates with incompleteness, indicating the XLF flattens at low-L(X). The composite XLF is well fitted by a power law with a break at (2.21(-0.56)(+0.65)) x 10(38) ergs s(-1) and beta = 1.40(-0.13)(+0.10) and 2.84(-0.30)(+0.39) below and above it, respectively. The break is close to the Eddington limit for a 1.4M(circle dot) neutron star, but the XLF shape rules out its representing the division between neutron star and black hole systems. Although the XLFs are similar, we find evidence of some variation between galaxies. The high-L(X) XLF slope does not correlate with age, but may correlate with [alpha/Fe]. Considering only LMXBs with L(X) > 10(37) ergs s(-1), matching the LMXBs with globular clusters (GCs) identified in HST observations of 19 of the galaxies, we find the probability a GC hosts an LMXB is proportional L(GC)(alpha)Z(Fe)(gamma) where alpha = 1.01 + 0.19 and gamma = 0.33 +/- 0.11. Correcting for GC luminosity and color effects, and detection incompleteness, we find no evidence that the fraction of LMXBs with L(X) > 10(37) ergs s(-1) in GCs (40%), or the fraction of GCs hosting LMXBs (similar to 6.5%) varies between galaxies. The spatial distribution of LMXBs resembles that of GCs, and the specific frequency of LMXBs is proportional to the GC specific luminosity, consistent with the hypothesis that all LMXBs form in GCs. If the LMXB lifetime is tau(L) and the duty cycle is F(d), our results imply similar to 1.5(tau(L)/10(8) yr)(-1) F(-1) LMXBs LMXBs are formed per gigayear per GC, and we place an upper limit of one active LMXB in the field per 3.4 x 10(9) L(circle dot) of V-band luminosity.