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 (HCO+)-C-13 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 (HCO+)-C-13 J = 1-0 line is optically thin, whereas the thermal SiO lines are optically thick. The line intensity in (HCO+)-C-13 J = 1-0 shows that the cloud has a large column density, up to N( H-2) = ( 6-7) x 10(23) cm(-2), which corresponds to about 640 - 740 mag in A(V) or 10 - 12 mag in A(25 mu m). 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 similar to 35".