H13CO+ and Thermal SiO Observations of G0.11–0.11; an Extremely Large Column Density Cloud

Abstract

A molecular cloud G0.11−0.11, which is located between the Galactic Center Arc (GCA) and Sgr A, was found from the NRO CS survey of the Galactic Center region [1]. Its morphology and velocity structure suggests that this cloud is interacting with GCA [2]. However, line intensity ratio of CS lines suggests they are optically thick (τ = 2 − 3) in the Galactic Center region [1]. To investigate the actical physical parameters and structure observations in optically thin line is required. Here, we observed the first view in HCO and in thermal SiO lines of G0.11−0.11 [3]. Using comparison of line intensities, we found the HCO line is optically thin, whereas the thermal SiO lines are optically thick. In the souther part the cloud has large column density up to N(H2) = (6− 7)× 1023cm−2, which corresponds to about 640−740 mag in AV or 10-12 mag in A25μm. This is the largest known any even in the Galactic Center region. The intensity ratio of SiO to CS lines suggests that emitting gas is highly inhomogeneous for SiO abundance on a scale smaller than the beam with about 35”.