New Look at the Molecular Superbubble Candidate in the Galactic Center

The $l\!=\!+1.\!\!^\circ3$ 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 {\it J}=1--0, $^{13}$CO {\it J}=1--0, H$^{13}$CN {\it J}=1--0, H$^{13}$CO$^{+}$ {\it J}=1--0, SiO {\it J}=2--1, and CS {\it J}=2--1 lines obtained from the Nobeyama radio observatory 45-m telescope, as well as CO {\it J}=3--2 maps obtained from the James Clerk Maxwell telescope. We identified eleven expanding shells with total kinetic energy and typical expansion time $E_{\rm kin}\!\sim\! 10^{51.9}$ erg and $t_{\rm exp}\!\sim\! 10^{4.9}$ yr, respectively. In addition, the $l\!=\!+1.\!\!^\circ3$ region exhibited high SiO {\it J}=2--1/H$^{13}$CN {\it J}=1--0 and SiO {\it J}=2--1/H$^{13}$CO$^{+}$ {\it 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 $l\!=\!+1.\!\!^\circ3$ 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 show the importance of compact broad-velocity-width features in searching for localized energy sources hidden behind severe interstellar extinction and stellar contamination.