A Panchromatic Study of the X-Ray Binary Population in NGC 300 on Subgalactic Scales

The population-wide properties and demographics of extragalactic X-ray binaries (XRBs) correlate with the star formation rates (SFRs), stellar masses ( M ⋆ ), and environmental factors (such as metallicity, Z ) of their host galaxy. Although there is evidence that XRB scaling relations ( L X /SFR for high-mass XRBs (HMXBs) and L X / M ⋆ for low-mass XRBs) may depend on metallicity and stellar age across large samples of XRB-hosting galaxies, disentangling the effects of metallicity and stellar age from stochastic effects, particularly on subgalactic scales, remains a challenge. We use archival X-ray through IR observations of the nearby galaxy NGC 300 to self-consistently model the broadband spectral energy distribution and examine radial trends in its XRB population. We measure a current (<100 Myr) SFR of 0.18 ± 0.08 M ⊙ yr −1 and stellar mass M ⋆ = ( 2.15 − 0.14 + 0.26 ) × 10 9 M ⊙ . Although we measure a metallicity gradient and radially resolved star formation histories that are consistent with the literature, there is a clear excess in the number of X-ray sources below ∼10 37 erg s −1 that are likely a mix of variable XRBs and additional background active galactic nuclei. When we compare the subgalactic L X /SFR ratios as a function of Z to the galaxy-integrated L X -SFR- Z relationships from the literature, we find that only the regions hosting the youngest (≲30 Myr) HMXBs agree with predictions, hinting at time evolution of the L X –SFR– Z relationship.