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 $\rm z\sim 0.6$ star-forminggalaxies using new SWIRE observations in IR and GALEX observations in UV. Twosamples are selected from the SWIRE and GALEX source catalogs in theSWIRE/GALEX field ELAIS-N1-00 ($\Omega = 0.8$ deg$^2$). The UV selected samplehas 600 galaxies with photometric redshift (hereafter photo-z) $0.5 \leq z \leq0.7$ and NUV$\leq 23.5$ (corresponding to $\rm L_{FUV} \geq 10^{9.6} L_\sun$).The IR selected sample contains 430 galaxies with $f_{24\mu m} \geq 0.2$ mJy($\rm L_{dust} \geq 10^{10.8} L_\sun$) in the same photo-z range. It is foundthat the mean $\rm L_{dust}/L_{FUV}$ ratios of the z=0.6 UV galaxies areconsistent with that of their z=0 counterparts of the same $\rm L_{FUV}$. ForIR galaxies, the mean $\rm L_{dust}/L_{FUV}$ ratios of the z=0.6 LIRGs ($\rmL_{dust} \sim 10^{11} L_\sun$) 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 consistentwith the hypothesis that the dominant component of LIRG population has changedfrom large, gas rich spirals at z$>0.5$ to major-mergers at z=0. The stellarmass of z=0.6 UV galaxies of $\rm L_{FUV} \leq 10^{10.2} L_\sun$ is about afactor 2 less than their local counterparts of the same luminosity, indicatinggrowth of these galaxies. The mass of z=0.6 UV lunmous galaxies (UVLGs: $\rmL_{FUV} > 10^{10.2} L_\sun$) and IR selected galaxies, which are nearlyexclusively LIRGs and ULIRGs, is the same as their local counterparts.Comment: 27 pages, 8 figures, to be published in the Astrophysical Journal Supplement series dedicated to GALEX result