Strong Evidence For Globular Cluster Low-mass X-ray Binaries Seeding The Field Population Within Nearby Elliptical Galaxies

Low-mass X-ray binaries (LMXBs) are thought to form through either dynamical interactions within dense stellar environments, such as globular clusters (GC LMXBs), or in situ via binary stellar evolution within the field of the galaxy (field LMXBs). Previous studies have suggested the GC LMXB population could be responsible for seeding the field population, either through ejection of GC LMXBs into the field or GC evaporation during encounters with parent galaxies. We investigate the origin of the field LMXB population, using a sample of 24 nearby (D < 25 Mpc), early-type galaxies that have coverage from both Chandra ACIS and two-color HST ACS imaging. We use these multi-wavelength data to classify each of the 2060 X-ray sources as GC LMXBs (620), background sources (110) or field LMXB candidates (1330), and we fit the X-ray luminosity function (XLF) for each source type. We find that the LMXB XLF of the field LMXB population both increases in normalization per stellar mass and flattens in slope with increasing GC specific frequency (number of GC per optical luminosity) providing strong evidence that GC LMXBs are indeed responsible for a non-negligible population of field LMXBs.