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-N1-00 (Ω = 0.8 deg^2). The UV-selected sample has 600 galaxies with photometric redshift (hereafter photo-z) 0.5 ≤ z ≤ 0.7 and NUV ≤ 23.5 (corresponding to L_(FUV) ≥ 10^(9.6) L_☉). The IR-selected sample contains 430 galaxies with f_(24 μm) ≥ 0.2 mJy (L_(dust) ≥ 10^(10.8) L_☉) in the same photo-z range. It is found that the mean L_(dust)/L_(FUV) ratios of the z = 0.6 UV galaxies are consistent with that of their z = 0 counterparts of the same L_(FUV). For IR galaxies, the mean L_(dust)/L_(FUV) ratios of the z = 0.6 LIRGs (L_(dust) ~ 10^(11) L_☉) are about a factor of 2 lower than local LIRGs, whereas z = 0.6 ULIRGs (L_(dust) ~ 10^(12) L_☉) have the same mean 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 L_(FUV) ≤ 10^(10.2) 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: L_(FUV) > 10^(10.2) L_☉) and IR-selected galaxies, which are nearly exclusively LIRGs and ULIRGs, is the same as their local counterparts.

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