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 $rm zsim 0.6$ 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 ($Omega = 0.8$ deg$^2$). The UV selected sample has 600 galaxies with photometric redshift (hereafter photo-z) $0.5 leq z leq 0.7$ and NUV$leq 23.5$ (corresponding to $rm L_{FUV} geq 10^{9.6} L_sun$). The IR selected sample contains 430 galaxies with $f_{24mu m} geq 0.2$ mJy ($rm L_{dust} geq 10^{10.8} L_sun$) in the same photo-z range. It is found that the mean $rm L_{dust}/L_{FUV}$ ratios of the z=0.6 UV galaxies are consistent with that of their z=0 counterparts of the same $rm L_{FUV}$. For IR galaxies, the mean $rm L_{dust}/L_{FUV}$ ratios of the z=0.6 LIRGs ($rm L_{dust} sim 10^{11} L_sun$) are about a factor of 2 lower than local LIRGs, whereas z=0.6 ULIRGs ($rm L_{dust} sim 10^{12} L_sun$) have the same mean $rm L_{dust}/L_{FUV}$ 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 $rm L_{FUV} leq 10^{10.2} L_sun$ is about a factor 2 less than their local counterparts of the same luminosity, indicating growth of these galaxies. The mass of z=0.6 UV lunmous galaxies (UVLGs: $rm L_{FUV} > 10^{10.2} L_sun$) and IR selected galaxies, which are nearly exclusively LIRGs and ULIRGs, is the same as their local counterparts.