New Look at the Molecular Superbubble Candidate in the Galactic Center

The $l\text{\hspace{0.17em}⁣}=\text{\hspace{0.17em}⁣}+1.\text{\hspace{0.17em}⁣}\text{\hspace{0.17em}⁣}{}^{\circ }3$ 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 {\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 $E_{\mathrm{k}\mathrm{i}\mathrm{n}}\text{\hspace{0.17em}⁣}\sim \text{\hspace{0.17em}⁣}{10}^{51.9}$ erg and $t_{\rm exp}!\sim! 10^{4.9}$yr,respectively\mathrm{.}Inaddition,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 $l\text{\hspace{0.17em}⁣}=\text{\hspace{0.17em}⁣}+1.\text{\hspace{0.17em}⁣}\text{\hspace{0.17em}⁣}{}^{\circ }3$ 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.