Dust Attenuation in the Nearby Universe: A Comparison between Galaxies Selected in the Ultraviolet and in the Far-Infrared

Abstract

We compare the dust attenuation properties of two samples of galaxies purely\nselected in the near-ultraviolet (NUV) band (1750-2750 A, lambda_m = 2310 A)\nand in the far-infrared (FIR) at 60micron. These samples are built using the\nGALEX and IRAS sky surveys over ~600 square degrees. The NUV selected sample\ncontains 95 galaxies detected down to NUV=16mag (AB system). 83 galaxies in\nthis sample are spirals or irregulars and only two of them are not detected at\n60micron. The FIR selected sample is built from the IRAS PSCz catalog complete\ndown to 0.6Jy. Among the 163 sources, we select 118 star forming galaxies well\nmeasured by IRAS, all but 1 are detected in NUV and 14 galaxies are not\ndetected in the far-ultraviolet (FUV) band (1350-1750 A, lambda_m = 1530 A).\nThe dust to ultraviolet (NUV and FUV) flux ratio is calibrated to estimate the\ndust attenuation at both wavelengths. The median value of the attenuation in\nNUV is found to be ~1 mag for the NUV selected sample versus ~2 mag for the FIR\nselected one. Within both samples, the dust attenuation is found to correlate\nwith the luminosity of the galaxies. Almost all the NUV selected galaxies and\n2/3 of the FIR selected sample exhibit a lower dust attenuation than that\nexpected from the tight relation found previously for starburst galaxies\nbetween the dust attenuation and the slope of the ultraviolet continuum. The\nsituation is inverse for one third of the FIR selected galaxies: their\nextinction is higher than that deduced from their FUV-NUV color and the\nrelation valid for starbursts.\n