IR and UV Galaxies at z = 0.6: Evolution of Dust Attenuation and Stellar Mass as Revealed by SWIRE and GALEX

Abstract

We study dust attenuation and stellar mass of z ∼ 0.6 star-forming galaxies using new SWIRE observations in IR and GALEX observations in UV. Two samples are selected from the SWIRE and GALEX source catalogs in the SWIRE/GALEX field ELAIS-Nl-00 (Ω = 0.8 deg2). The UV-selected sample has 600 galaxies with photometric redshift (hereafter photo-z) 0.5 ≤ z ≤ 0.7 and NUV ≤ 23.5 (corresponding to LFUV ≥ 109.6 L ⊙). The IR-selected sample contains 430 galaxies with f 24μm ≥ 0.2 mJy (Ldust ≥ 1010.8 L ⊙) in the same photo-z range. It is found that the mean L dust/LFUV ratios of the z = 0.6 UV galaxies are consistent with that of their z = 0 counterparts of the same LFUV-For IR galaxies, the mean Ldust/LFUV ratios of the z = 0.6 LIRGs (Ldust ∼ 1011 L⊙) are about a factor of 2 lower than local LIRGs, whereas z = 0.6 ULIRGs (Ldust ∼ 1012 L⊙) have the same mean Ldust/L FUV ratios as their local counterparts. This is consistent with the hypothesis that the dominant component of LIRG population has changed from large, gas-rich spirals at z > 0.5 to major mergers at z = 0. The stellar mass of z = 0.6 UV galaxies of LFUV ≤ 1010.2 L ⊙ is about a factor of 2 less than their local counterparts of the same luminosity, indicating growth of these galaxies. The mass of z = 0.6 UV luminous galaxies (UVLGs: LFUV > 1010.2 L ⊙) and IR-selected galaxies, which are nearly exclusively LIRGs and ULIRGs, is the same as their local counterparts. © 2007. The American Astronomical Society. All rights reserved.