2010A&A...523A..45R

A large-scale survey of the Galactic center region in the 3mm 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. Using the NANTEN 4m telescope from Nagoya University, a region between -5.75<l<5.6deg and -0.68<b<1.3deg 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⁺). 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 4.9x10^–3 and for disk clouds of 3.4x10^–3. The luminosity ratio of HCO⁺(J=1-0)/CO(J=1-0) in the Galactic center is 3.5x10^–2, and for disk clouds it is 1.5x10^–2. We can distinguish clearly between regions where the SiO or HCO⁺ dominate.