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 $\mathrm{z}\sim 0.6$ 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 ($\hat{I}\text{c◯}=0.8$ deg${}^2$). The UV selected sample has 600 galaxies with photometric redshift (hereafter photo-z) $0.5\le z\le 0.7$ and NUV$\le 23.5$ (corresponding to $\rm L_{FUV} \geq 10^{9.6} L_\sun$). The IR selected sample contains 430 galaxies with $f_{24\hat{I}¼m}\ge 0.2$ mJy ($\rm L_{dust} \geq 10^{10.8} L_\sun$) in the same photo-z range. It is found that the mean ${\mathrm{L}}_{\mathrm{dust}}/{\mathrm{L}}_{\mathrm{FUV}}$ ratios of the z=0.6 UV galaxies are consistent with that of their z=0 counterparts of the same ${\mathrm{L}}_{\mathrm{FUV}}$. For IR galaxies, the mean ${\mathrm{L}}_{\mathrm{dust}}/{\mathrm{L}}_{\mathrm{FUV}}$ 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 ${\mathrm{L}}_{\mathrm{dust}}/{\mathrm{L}}_{\mathrm{FUV}}$ 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.

27 pages, 8 figures, to be published in the Astrophysical Journal Supplement series dedicated to GALEX results