| Description |
Due to its proximity, our Galactic Center provides a unique opportunity to study the physical processes that occur within (extra)galactic nuclei with unprecedented sensitivity and spatial resolution. Herschel provides the only opportunity to probe the detailed physical conditions of the circumnuclear neutral material and the feedback processes with the central energy source(s) in our own Galaxy, and by extension in other galactic nuclei. We propose to acquire wide range (51 to 670 micron) spectral maps towards the atomic and molecular gas surrounding SgrA. Combining data from the PACS and SPIRE instruments, we will establish a complete inventory of the FIR spectrum accessible to Herschel across the central 5 arcmin (12 pc) of the Galaxy. Our immediate goal is to characterize the physical and chemical conditions of the gas in both the central (ionized) cavity and in the surrounding neutral gas (often referred to as circumnuclear disk, or CND) that is presumably the reservoir of material that can flow to the central black hole. Our supporting ground-based and first targeted HIFI observations show a high-excitation state of the molecular gas in the CND, with a strong radial excitation gradient across the disk and a very sharp inner transition zone to the central cavity. These early data resemble the hard XDR-type CO line SED observed towards e.g. Mrk231.Herschel data cover lines from energy levels needed to constrain the conditions within, and energetics of the CND. We will use state-of-the-art XDR/PDR models that include multiple heating processes (a.o., shock, dissipation of turbulence) to interpret the data. The data product will be one of Herschel.s legacies in the detailed study of galactic nuclei. This data set, with high sensitivity, high spatial resolution, and broad wavelength coverage, will be an essential resource for many studies of the Galactic Center. No comparable study of this region will be possible for many years to come. |
