Linking the X-ray and infrared properties of star-forming galaxies at z < 1.5

We present the most complete study to date of the X-ray emission from star formation in high-redshift (median z = 0.7; z -3 in both hard and soft X-ray bands. From the sources which are star formation dominated, only a small fraction are individually X-ray detected and for the bulk of the sample we calculate average X-ray luminosities through stacking. We find an average soft X-ray to infrared ratio of log (LSX/LIR) = -4.3 and an average hard X-ray to infrared ratio of log (LHX/LIR)=-3.8.We report that the X-ray/IR correlation is approximately linear through the entire range of LIR and z probed and, although broadly consistent with the local (z < 0.1) one, it does display some discrepancies. We suggest that these discrepancies are unlikely to be physical, i.e. due to an intrinsic change in the X-ray properties of star-forming galaxies with cosmic time, as there is no significant evidence for evolution of the LX/LIR ratio with redshift. Instead, they are possibly due to selection effects and remaining AGN contamination. We also examine whether dust obscuration in the galaxy plays a role in attenuating X-rays from star formation, by investigating changes in the LX/LIR ratio as a function of the average dust temperature. We conclude that X-rays do not suffer any measurable attenuation in the host galaxy. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society