A Panchromatic Study of the X-ray Binary Population in NGC 300 on Sub-Galactic Scales
arxiv(2024)
摘要
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 [LMXBs]) 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 M_⋆=
(2.15^+0.26_-0.14)×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 AGN. 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.
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