Herschel / HerMES : the X - ray – infrared correlation for star - forming galaxies at z ∼ 1

For the first time, we investigate the X-ray/infrared (IR) correlation for star-forming galaxies (SFGs) at z ∼ 1, using SPIRE submm data from the recently launched Herschel Space Observatory and deep X-ray data from the 2-Ms Chandra Deep Field-North 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 SFGs to equivalently IR-luminous (LIR > 1010 L ) 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 E-mail: [email protected] C © 2011 The Authors Monthly Notices of the Royal Astronomical Society C © 2011 RAS 2240 M. Symeonidis et al. luminosity, with luminous and ultraluminous IR galaxies (LIRGs and ULIRGs; LIR > 1011 L ) having up to an order of magnitude lower values than normal IR galaxies (LIR < 1011 L ). 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.