Sub-galactic scaling relations between X-ray luminosity, star-formation rate, and stellar mass

Abstract

X-ray luminosity ($L_X$) originating from high-mass X-ray binaries (HMXBs) is tightly correlated with the host galaxy's star-formation rate (SFR). We explore this connection at sub-galactic scales spanning $\sim$7 dex in SFR and $\sim$8 dex in specific SFR (sSFR). There is good agreement with established relations down to $\mathrm{SFR}\simeq 10^{-3}{\mathrm{M}}_{\odot }\mathrm{y}{\mathrm{r}}^{-1}$, below which an excess of X-ray luminosity emerges. This excess likely arises from low mass X-ray binaries. The intrinsic scatter of the $L_X$-SFR relation is constant, not correlated with SFR. Different star formation indicators scale with $L_X$ in different ways, and we attribute the differences to the effect of star formation history. The SFR derived from H$\alpha$ shows the tightest correlation with X-ray luminosity because H$\alpha$ emission probes stellar populations with ages similar to HMXB formation timescales, but the H$\alpha$-based SFR is reliable only for $\mathrm{sSFR}>10^{-12}{\mathrm{M}}_{\odot }\mathrm{y}{\mathrm{r}}^{-1}/{\mathrm{M}}_{\odot }$.

19 pages, 13 figures, accepted for publication in MNRAS (2020-04-19)

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Cited by in corpus (2)

• A census of ultraluminous X-ray sources in the local Universe
• The Metallicity Dependence of the High-Mass X-ray Binary Luminosity Function