A Blind Survey of the Local Dusty Universe with Herschel-ATLAS

A blind survey of the nearby dusty galaxies detected by Herschel-ATLAS reveals that 75% are, unexpectedly, irregular and/or highly flocculent in morphology. They also tend to exhibit extremely blue UV-NIR colour; these galaxies are bluer than 90% of galaxies seen in targeted dust surveys. They are also colder, with a median dust temperature of only 17 K, and are 3 times dustier. Most have greater gas mass than stellar mass, with a median atomic gas fraction of 51%, with values ranging as high as 99%. %R 2013lcdu.confE..75K %B Heavy elements are formed by nucleosynthesis in the process of stellar evolution, and a significant fraction of the amount produced is injected into interstellar space in the form of dust grains. Dust grains scatter and absorb ultraviolet (UV) and optical emission from stars, and re-emit the absorbed energy as infrared (IR) radiation. This process prevents us from directly observing stellar light from galaxies. To understand the intrinsic properties of galaxies from their spectra, we must take into account both dust extinction and re-emission by dust. In this study, we construct spectral energy distribution (SED) models of galaxies as a function of galactic chemical evolution, taking into account dust extinction and re-emission. We use the evolutionary synthesis code “PEGASE”[1] to obtain stellar spectra of galaxies. We used extinction curves of [2], [3] and [4], and employ [6] for dust re-emission spectra. We calculated the evolution of the SEDs of galaxies. These results lead us to three conclusions. First, these SEDs have similar shapes and they behave similarly with time. Second, galaxies can be observed as luminous IR galaxies when galactic age is about from 500 Myr to 1 Gyr. Finally, present-day optically luminous galaxies were bright in IR in previous times. By using this model we can determine the metallicity in galaxies as a function of galactic age and calculate the dust extinction and re-emission consistently with metallicity. We can estimate the star formation rate, metallicity, dust abundance and other important quantities of high-z galaxies by fitting this model to SEDs observed for high-z sources.