The Observation of the Nearby Universe in UV and in FIR: an evidence for a moderate extinction in present day star forming galaxies

Abstract

We study the FIR and UV-visible properties of nearby star forming galaxies. This comparison is performed using the local luminosity functions at UV and FIR wavelengths and on individual starburst galaxies for which photometric data from UV to NIR and FIR are available. The comparison of the FIR and UV local luminosity functions argues for a moderate extinction in nearby disk galaxies. For a sample of 22 starburst galaxies, it is found that the UV(912-3650AA), the visible(3600-12500 AA) and the NIR(12500-22000 AA) wavelength range contribute 30%, 50% and 20% respectively to the total emerging stellar emission. The mean ratio of the dust to bolometric luminosity of these galaxies is 0.37+/-0.22 similar to the ratio found for normal spiral galaxies. The mean extinction at 2000AA is found to be ~1.2mag although with a large dispersion. The conversion factor of the stellar emission into dust emission is found to correlate with the luminosity of the galaxies, brighter galaxies having a higher conversion factor. We conclude that a very large conversion of the stellar light into dust emission can no longer be assumed as a general property of starburst galaxies at least in the local Universe. We compare the UV properties of our local starburst galaxies to those of high redshift galaxies. The larger extinction found in the distant galaxies is consistent with the trend we find for the nearby starburst galaxies namely the brighter the galaxies the lower the escape fraction of stellar light.