S. Mineo, G. Fabbiano, R. D'Abrusco, T. Fragos, D. -W. Kim, J. Strader, J. P. Brodie, J. S. Gallagher, A. Zezas, B. Luo
We report on a detailed investigation of the spatial distribution of the low-mass X-ray binary (LMXB) population in the elliptical galaxy NGC 4649. Using Chandra and Hubble data we separate the field and globular cluster (GC) populations. We find that on average the population of GCs with LMXBs has the same radial distribution as the parent red and blue GC distributions. Red GCs contain 3.3 times more LMXBs than blue GCs as already reported for this galaxy in previous works. There is a clear agreement between the radial profile for field LMXBs and the V-band profile within the D25 of NGC 4649. An excess of field LMXBs with respect to the V-light is observed in the galaxy's outskirts, likely due to unidentified GC sources or natal kicks. The radial profile of LMXBs in red GCs is fairly consistent with the stellar mass profile of the host galaxy but not near the galaxy center, where a lack of LMXBs is evident. We find that LMXBs in red GCs are on average more luminous than LMXBs in the field. We construct a stellar mass surface density map using a combination of 2MASS H-band and SDSS g- and i-band images. Using the map we prove that the global galaxy-wide relations between cumulative number and luminosity of LMXBs and the integrated stellar mass hold on local scales, except for the disagreement at large radii/small mass densities. We find statistically significant differences between the field-LMXB populations in high and low stellar mass density regimes.
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http://arxiv.org/abs/1306.6490
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