A survey of the Galactic center region in HCO+, H 13CO+, and SiO

Abstract

Aims. A large-scale survey of the Galactic center region in the 3 mm rotational transitions of SiO, HCO+ and H13CO+ (beamsize ∼3′.6) was conducted to provide an estimate of cloud conditions, heating mechanisms, chemistry, and other properties. Methods. Using the NANTEN 4 m telescope from Nagoya University, a region between -5°75 < l < 5°6 and -0°68 < b < 1°3 was mapped in the J = 1 →0 lines of HCO+ and H13CO+ and in the J = 2 → 1 line of SiO with a spacing of 3°75 (HCO+) and 1→875 (SiO and H13CO+). Results. Velocity channel maps, longitude-velocity maps, and latitude-velocity maps are presented. We identify 51 molecular clouds; 33 of them belong to the Galactic center and 18 to disk gas. We derive an average of the luminosity ratio of SiO(J = 2 → 1)/CO(J = 1 →0) in clouds belonging to the Galactic center of 4.9 × 10-3 and for disk clouds of 3.4 × 10-3. The luminosity ratio of HCO+(J = 1 →0)/CO(J = 1 →0) in the Galactic center is 3.5 × 10-2, and for disk clouds it is 1.5 × 10-2. We can distinguish clearly between regions where the SiO or HCO+ dominate. © 2010 ESO.