Detection of HD in emission towards Sagittarius B2

Abstract

The giant molecular cloud Sagittarius B2, located near the Galactic Centre, has been observed in the far-infrared by the ISO Long Wavelength Spectrometer. Wavelengths in the range 47-196 mu m were covered with the high resolution Fabry-Pérot spectrometer, giving a spectral resolution of 30-40 km s^-1. The J=1->0 and J=2->1 rotational transitions of HD fall within this range at 112 mu m and 56 mu m. A probable detection was made of the ground state J=1->0 line in emission but the J=2->1 line was not detected above the noise. This allowed us to calculate an upper limit on the temperature in the emitting region of approximately 80 K and a value for the deuterium abundance in the Sgr B2 envelope of D/H=(0.2-11)*E^-6. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, The Netherlands and the UK) with the participation of ISAS and NASA.