New Look at the Molecular Superbubble Candidate in the Galactic Center

Shiho Tsujimoto,Shoko Kanno,Ryosuke Nakagawara,Sonomi Nishiyama,Yuhei Iwata,Shunya Takekawa,Akira Kawakami,Asaka Uruno,Tomoharu Oka,Yuto Watanabe,Takuma Ogawa,Hiroki Yokozuka,Miyuki Kaneko

doi:10.3847/1538-4357/abe61e

Abstract

Abstract 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, 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 ∼ 1051.9 erg and t exp ∼ 104.9 yr, respectively. In addition, the l = +13 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 = +13 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.

Highlights

The Galactic center contains a large quantity of warm (Tk = 30–60 K) and dense [n (H2) ≥ 104 cm−3] molecular gas (Morris et al 1983; Paglione et al 1998)
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
In addition to the ubiquity of shock-origin molecules (Huttemeister et al 1998; Requena-Torres et al 2006), the highly turbulent kinematics of molecular gas in the central molecular zone (CMZ) can be attributed to the release of kinetic energy by numerous supernova (SN) explosions

Summary

Introduction

Gases in the central molecular zone (CMZ; Morris & Serabyn 1996) exhibit highly turbulent and complex kinematics with large velocity dispersions (Oka et al 1998b). In addition to the ubiquity of shock-origin molecules (Huttemeister et al 1998; Requena-Torres et al 2006), the highly turbulent kinematics of molecular gas in the CMZ can be attributed to the release of kinetic energy by numerous supernova (SN) explosions. Despite the abundance of dense molecular gas, star formation is currently inactive in the CMZ. The current star formation rate (SFR) ∼ 0.04–0.1 M ⊙ yr−1 (Yusef-Zadeh et al 2009; Immer et al 2012) is at least an order of magnitude lower than that expected from the amount of dense gas in the CMZ (Kruijssen et al 2014)

Results

Discussion

Conclusion