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 (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 (L_(IR) > 10^(10) 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 L_(SX)/L_(IR) and L_(HX)/L_(IR) ratios with redshift. We note, however, that at all redshifts, both L_(SX)/L_(IR) and L_(HX)/L_(IR) are strongly dependent on IR luminosity, with luminous and ultraluminous IR galaxies (LIRGs and ULIRGs; L_(IR) > 10^(11) L_⊙) having up to an order of magnitude lower values than normal IR galaxies (L_(IR) < 10^(11) L_⊙). We derive a L_(SX)–L_(IR) relation and confirm the applicability of an existing L_(HX)–L_(IR) relation for both local and distant LIRGs and ULIRGs, consistent with a scenario where X-ray luminosity is correlated with the star formation rate.

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