An overview of the Dwarf Galaxy Survey

Abstract

The Dwarf Galaxy Survey (DGS) program is studying low-metallicity galax- ies using 230h of far-infrared (FIR) and submillimetre (submm) photometric and spectroscopic observations of the Herschel Space Observatory and draws to this a rich database of a wide range of wavelengths tracing the dust, gas and stars. This sample of 50 galaxies includes the largest metallicity range achievable in the local Universe including the lowest metallicity (Z) galaxies, 1/50 Z⊙, and spans 4 orders of magnitude in star formation rates. The survey is designed to get a handle on the physics of the interstellar medium (ISM) of low metallicity dwarf galaxies, especially on their dust and gas properties and the ISM heating and cooling processes. The DGS produces PACS and SPIRE maps of low-metallicity galaxies observed at 70, 100, 160, 250, 350, and 500 μm with the highest sensi- tivity achievable to date in the FIR and submm. The FIR fine-structure lines, [CII] 158μm, [OI] 63μm, [OI] 145μm, [OIII] 88μm, [NIII] 57μm and [NII] 122 and 205 μm have also been observed with the aim of studying the gas cooling in the neutral and ionized phases. The SPIRE FTS observations include many CO lines (J=4-3 to J=13-12), [NII] 205 μm and [CI] lines at 370 and 609 μm. This paper describes the sample selection and global properties of the galaxies, the observing strategy as well as the vast ancillary database available to comple- ment the Herschel observations. The scientific potential of the full DGS survey is described with some example results included.