X-Ray emission from star-forming galaxies - III. Calibration of the LX-SFR relation up to redshift z ≈ 1.3

Abstract

We investigate the relation between total X-ray emission from star-forming galaxies and their star formation activity. Using nearby late-type galaxies and ultraluminous infrared galaxies from Paper I and star-forming galaxies from Chandra Deep Fields (CDFs), we construct a sample of 66 galaxies spanning the redshift range z ≈ 0-1.3 and the star formation rate (SFR) range~0.1-103M⊙ yr-1. In agreement with previous results, we find that the LX-SFR relation is consistent with a linear law both at z = 0 and for the z = 0.1-1.3 CDF galaxies, within the statistical accuracy of ~0.1 in the slope of the LX-SFR relation. For the total sample, we find a linear scaling relation LX/SFR ≈ (4.0 ± 0.4) x 1039(erg s-1)/(M⊙ yr-1), with a scatter of ≈0.4 dex. About ~2/3 of the 0.5-8 keV luminosity generated per unit SFR is expected to be due to high-mass X-ray binaries.We find no statistically significant trends in the mean LX/SFR ratio with the redshift or SFR and constrain the amplitude of its variations by ≲ 0.1-0.2 dex. These properties make X-ray observations a powerful tool to measure the SFR in normal star-forming galaxies that dominate the source counts at faint fluxes. © 2013 The Authors.