Tata Institute of Fundamental Research, Mumbai, India
Discovering the wealth in Velocity-resolved observations of Photon Dominated Regions
Photon Dominated Regions (PDRs) are regions where far-ultraviolet (FUV) (6eV<E<13.6eV) radiation from young massive stars dominate the physics and the chemistry of the interstellar medium (Tielens & Hollenbach 1985). The PDRs play an important role in reprocessing much of the energy from stars and re-emitting this energy in the infrared-millimeter regime. Hence PDRs which represent a significant fraction of neutral material in a galaxy are crucial towards understanding the star formation history & evolution of galaxies. PDR studies require dedicated far-infrared observations since the primary tracers of such gas are the fine-structure lines of C+ at 158 micron and atomic oxygen at 63 & 145 micron. Herschel & SOFIA have vastly changed the landscape for PDR research by virtue of the velocity information obtained with heterodyne instruments HIFI and GREAT/upGREAT respectively onboard. I will talk about the energetics, velocity fields and imhomogeneity of PDR gas that we observed in a few Galactic PDRs using the GREAT & upGREAT spectrometers onboard. These results will also motivate the specific instrumentation needs of the PDR community.