A survey of the Galactic center region in HCO+, H13CO+, and SiO

Abstract

Aims. A large-scale survey of the Galactic center region in the 3 mm rotational transitions of SiO, HCO+ and (HCO+)-C-13 (beamsize similar to 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 degrees.75 < l < 5 degrees.6 and -0 degrees.68 < b < 1 degrees.3 was mapped in the J = 1 -> 0 lines of HCO+ and (HCO+)-C-13 and in the J = 2 -> 1 line of SiO with a spacing of 3'.75 (HCO+) and 1'.875 (SiO and (HCO+)-C-13).

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 x 10(-3) and for disk clouds of 3.4 x 10(-3). The luminosity ratio of HCO+(J = 1 -> 0)/CO(J = 1 -> 0) in the Galactic center is 3.5 x 10(-2), and for disk clouds it is 1.5 x 10(-2). We can distinguish clearly between regions where the SiO or HCO+ dominate.