Herschel study of the ISM in Local Group dwarf ellipticals

Taking into consideration that dwarf galaxies are by number the dominant population in the currentUniverse and are considered as the main building blocks for more massive galaxies, studying their origin and evolution allows putting strong constraints on cosmological parameters.Especially, the ISM of metalpoor dwarf galaxies provides an interesting laboratory to study the outcome of stellar feedback and the effect of this metalenrichment on future star formation.Since dwarfs with a low metal abundance are the best presentday representatives for theconditions in the early Universe, they offer the best opportunity to learn more about the evolutionof this galaxy type throughout the history of the Universe. In particular, the proximity of theLocal Group enables spatially resolved studies of the lowest surface brightness dwarf galaxiesand benefits from a wealth of available ancillary data.NGC 205, NGC 185 and NGC 147 are three metalpoor dwarf elliptical companions of M31,featuring a ten times less massive gaseous component than predicted from theoretical starfomation models. Either efficient supernova feedback or the presence of a more diffuse ISMcomponent are thought to be responsible for the missing ISM problem.We propose to probe the ISM through the continuum emission from dust, to better constrainthe ISM mass. Recent Herschel observations for NGC 205 confirm the missing ISM problemin this galaxy. We propose to probe the ISM in NGC 185 and NGC 147 with Herschel. With a dust mass detection limit of virgul10^2 Msun, SPIRE observations are considered capableof detecting the ISM in NGC147 for the very first time. The unprecedented resolution at PACSwavelengths allows spatially resolved studies of the dust heating mechanisms,dust characteristics (temperature, composition, distribution) and its correlation with thegaseous component, which well shed light on the typical star formation conditions and,in this way, allow a be tru [truncated!, Please see actual data for full text]