Thermal SiO and H¹³CO⁺Line Observations of the Dense Molecular Cloud G0.11−0.11 in the Galactic Center Region

We obtained the first view in H¹³CO⁺ $J=1-0$ and a high resolution map in thermal SiO lines of G0.11$-$0.11, which is a molecular cloud situated between the Galactic Center radio arc and Sgr A. From a comparison with previous line observations, we found that the H¹³CO⁺ $J=1-0$ line is optically thin, whereas the thermal SiO lines are optically thick. The line intensity in H¹³CO⁺ $J=1-0$ shows that the cloud has a large column density, up to N(H₂)=(6-7)×10²³ cm⁻², which corresponds to about 640--740 mag in AV or 10--12 mag in A₂₅. The estimated column density is the largest known of any even in the Galactic center region. We conclude from the intensity ratio of SiO $J=1-0$ to CS $J=1-0$ that emitting gas is highly inhomogeneous for SiO abundance on a scale smaller than the beam width ~35.