Herschel/HerMES: The X-ray - Infrared correlation for star-forming galaxies at z~1

Abstract

For the first time, we investigate the X-ray/infrared (IR) correlation for star-forming galaxies at z~1, using SPIRE submm data from the recently-launched Herschel Space Observatory and deep X-ray data from the 2Ms Chandra deep field north (CDFN) survey. We examine the X-ray/IR correlation in the soft X-ray (SX, 0.5-2 keV) and hard X-ray (HX, 2-10 keV) bands by comparing our z~1 SPIRE-detected star-forming galaxies (SFGs) to equivalently IR-luminous (LIR >1010 Lsun) samples in the local/low redshift Universe. Our results suggest that the X-ray/IR properties of the SPIRE SFGs are on average similar to those of their local counterparts, as we find no evidence for evolution in the LSX/LIR and LHX/LIR ratios with redshift. We note however, that at all redshifts, both LSX/LIR and LHX/LIR are strongly dependent on IR luminosity, with luminous and ultraluminous infrared galaxies (LIRGs and ULIRGs,LIR >1011 Lsun) having up to an order of magnitude lower values than normal infrared galaxies (LIR <1011 Lsun). We derive a LSX-LIR relation and confirm the applicability of an existing LHX-LIR relation for both local and distant LIRGs and ULIRGs, consistent with a scenario where X-ray luminosity is correlated with the star-formation rate (SFR).

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