New Look at the Molecular Superbubble Candidate in the Galactic Center

The l = +1°3 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, ¹³CO J = 1-0, H¹³CN J = 1-0, H¹³CO⁺ 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 = +1°3 region exhibited high SiO J = 2-1/H¹³CN J = 1-0 and SiO J = 2-1/H¹³CO⁺ 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 = +1°3 region. The nature of the embedded star cluster, which may have supplied 20-70 supernova explosions within 10⁵ 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.