Lx-SFR-Z Relationship in NGC 300

We examine the relationship between the integrated X-ray luminosity (LX) of high mass X-ray binaries (HMXBs), star formation rate (SFR), and metallicity (Z) on sub-galactic scales within the nearby star-forming galaxy NGC 300 using new and archival Chandra/ACIS-I observations in conjunction with Hubble ACS and WFC, GALEX FUV, and Spitzer 24 μm imaging. We use a Bayesian optimized inference code to identify sources as likely X-ray binaries (XRBs) based on their projected location within NGC 300, their X-ray spectral shape, long- and short-term X-ray variability, and multiwavelength properties, and we determine the most probable Z of each XRB based on the published metallicity gradient in NGC 300. The XRB candidates are sorted into subsamples based on galactocentric distance (a proxy for metallicity), and X-ray luminosity functions down to ~10^36 erg/s are obtained and modeled as a linear combination of high- and low-mass X-ray binary components. The LX-SFR-Z relationship for high-mass XRBs is significantly steeper than reported in previous studies. We propose that this steeper slope is the result of two factors: (1) the use of direct metallicity measurements from stars and auroral nebular emission compared to metallicities inferred from strong-line methods, and (2) the “washing out” of metallicity gradients and variations that occurs in galaxy-integrated studies.