The ACS Virgo Cluster Survey.: III.: Chandra and Hubble Space Telescope observations of low-mass X-ray binaries and globular clusters in M87

The ACIS instrument on board the Chandra X-Ray Observatory has been used to carry out the first systematic study of low-mass X-ray binaries (LMXBs) in M87, the giant elliptical galaxy near the dynamical center of the Virgo Cluster. These images-with a total exposure time of 154 ks-are the deepest X-ray observations yet obtained of M87. We identify 174 X-ray point sources, of which similar to150 are likely LMXBs. This LMXB catalog is combined with deep F475W and F850LP images taken with ACS on the Hubble Space Telescope (HST) ( as part of the ACS Virgo Cluster Survey) to examine the connection between LMXBs and globular clusters in M87. Of the 1688 globular clusters in our catalog, f(X) = 3.6% +/- 0.5% contain an LMXB. Dividing the globular cluster sample by metallicity, we find that the metal-rich clusters are 3 +/- 1 times more likely to harbor an LMXB than their metal-poor counterparts. In agreement with previous findings for other galaxies based on smaller LMXB samples, we find the efficiency of LMXB formation to scale with both cluster metallicity Z and luminosity, in the sense that brighter, more metal-rich clusters are more likely to contain an LMXB. For the first time, however, we are able to demonstrate that the probability p(X) that a given cluster will contain an LMXB depends sensitively on the dynamical properties of the host cluster. Specifically, we use the HST images to measure the half-light radius, concentration index, and central density rho(0) for each globular and define a parameter Gamma, which is related to the tidal capture and binary-neutron star exchange rate. Our preferred form for p(X) is then p(X) proportional to Gamma rho(0)(0.42+/-0.11)(Z/Z(.))(0.33+/-0.1). We argue that if the form of p(X) is determined by dynamical processes, then the observed metallicity dependence is a consequence of an increased number of neutron stars per unit mass in metal-rich globular clusters. Finally, we present a critical examination of the LMXB luminosity function in M87 and reexamine the published LMXB luminosity functions for M49 and NGC 4697. We find no compelling evidence for a break in the luminosity distribution of resolved X-ray point sources in any of these galaxies. Instead, the LMXB luminosity function in all three galaxies is well described by a power law with an upper cutoff at L-X similar to 10(39) ergs s(-1).