The 3 mm lines of HCO+2 and HNCO have been observed toward Sgr B2. Besides the well-known "principal cloud" and an extended envelope, we find another gas cloud 2' north of Sgr B2(M). This 2' north (2' N) cloud which may be located behind the principal cloud, has a total mass of ~105 M and a diameter of ~7 pc. HCO+2 and HNCO exist mainly at 2' north, and their column densities are about 2.2 × 1014 and 2.3 × 1015 cm-2, respectively. The fractional abundances of these species relative to molecular hydrogen appear to be enhanced by at least a factor of 10 compared to the principal cloud. We have also identified redshifted and blueshifted high-velocity components which move toward the 2' N position with projected velocities of ±30 km s-1. These components are located symmetrically around 2' N, along the Galactic plane, and have diameters of about 4-5 pc and masses of ~1 × 104 M. The flow energies are large enough to initiate new star formation in the 2' N region on the free-fall timescale of 105 yr. This large-scale collapsing motion may cause a strong shock in the 2' N cloud and result in the enhancement of HCO+2 and HNCO.
Available at: http://works.bepress.com/wirvine/41/