The link between SCUBA andSpitzer: cold galaxies atz≲ 1

Abstract

We show that the far-IR properties of distant Luminous and Ultraluminous InfraRed Galaxies (LIRGs and ULIRGs) are on average divergent from analogous sources in the local Universe. Our analysis is based on Spitzer MIPS and IRAC data of L_IR>10^10 L_solar, 70um-selected objects in the 0.1<z<2 redshift range and supported by a comparison with the IRAS Bright Galaxy Sample. The majority of the objects in our sample are described by Spectral Energy Distributions (SEDs) which peak at longer wavelengths than local sources of equivalent total infrared luminosity. This shift in SED peak wavelength implies a noticeable change in the dust and/or star-forming properties from z~0 to the early Universe, tending towards lower dust temperatures, indicative of strong evolution in the cold dust, `cirrus', component. We show that these objects are potentially the missing link between the well-studied local IR-luminous galaxies, Spitzer IR populations and SCUBA sources -- the z<1 counterparts of the cold z>1 SubMillimetre Galaxies (SMGs) discovered in blank-field submillimetre surveys. The Herschel Space Observatory is well placed to fully characterise the nature of these objects, as its coverage extends over a major part of the far-IR/submm SED for a wide redshift range.