New Look at the Molecular Superbubble Candidate in the Galactic Center

The l = +13 region in the Galactic center is characterized by multiple shell-like structures and their extremely broad velocity widths. We revisit the molecular superbubble hypothesis for this region, based on high-resolution maps of CO J = 1–0, 13 CO J = 1−0, H 13 CN J = 1−0, H 13 CO + J = 1−0, SiO J = 2−1, and CS J = 2−1 lines obtained from the Nobeyama Radio Observatory 45 m telescope, as well as CO J = 3−2 maps obtained from the James Clerk Maxwell telescope. We identified 11 expanding shells with total kinetic energy and typical expansion time E kin ∼ 10 51.9 erg and t exp ∼ 10 4.9 yr, respectively. In addition, the l = +13 region exhibited high SiO J = 2−1/H 13 CN J = 1−0 and SiO J = 2−1/H 13 CO + J = 1−0 intensity ratios, indicating that the region has experienced dissociative shocks in the past. These new findings confirm the molecular superbubble hypothesis for the l = +13 region. The nature of the embedded star cluster, which may have supplied 20–70 supernova explosions within 10 5 yr, is discussed. This work also shows the importance of compact broad-velocity-width features in searching for localized energy sources hidden behind severe interstellar extinction and stellar contamination.