The Evolution of Normal Galaxy X-ray Emission Through Cosmic History: Constraints from the 6 Ms Chandra Deep Field-South

Understand

We present measurements of the evolution of normal-galaxy X-ray emission from $z \approx$ 0-7 using local galaxies and galaxy samples in the 6 Ms Chandra Deep Field-South (CDF-S) survey.

• The majority of the CDF-S galaxies are observed at rest-frame energies above 2 keV, where the emission is expected to be dominated by X-ray binary (XRB) populations; however, hot gas is expected to provide small contributions to the observed- frame < 1 keV emission at $z < 1$.
• We show that a single scaling relation between X-ray luminosity ($L_{\rm X}$) and star-formation rate (SFR) is insufficient for characterizing the average X-ray emission at all redshifts.
• We establish that scaling relations involving not only SFR, but also stellar mass ($M_\star$) and redshift, provide significantly improved characterizations of the average X-ray emission from normal galaxy populations at $z \approx$ 0-7.