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

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-N1-00 (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 f24 μ m ⩾ 0.2 mJy (Ldust ⩾ 1010.8 L☉) in the same photo-z range. It is found that the mean Ldust/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/LFUV 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.