Detection of Eight Molecular Supershells in the Southern Milky Way with NANTEN

Abstract

Abstract We carried out a new CO survey for molecular supershells in the southern Milky Way with NANTEN. We covered an area of $300^{\circ} \lt l \lt 350^{\circ}$ and $-9^{\circ} \lt b \lt 9^{\circ}$ at $4^{\prime}$ or $8^{\prime}$ grid spacings with a 2.$^\prime$6 beamsize. In addition to the disk component at $\vert b\vert \lt 2^{\circ}$, we found numerous filamentary or arc-like CO distributions by inspecting the velocity channel maps. As a result, we identified 8 supershell candidates, 3 of which are associated with CO holes in the galactic disk. Six of the supershells had not been identified by the previous studies, while 2 of them were known from H i and low-resolution CO surveys. The size of the supershells ranges from 100 pc to 450 pc and the average is 230 pc; their age ranges from $2.2 \times 10^6 \;\mathrm{yr}$ to $1.1 \times 10^7 \,\mathrm{yr}$. We note that two of the supershells are also associated with observable indications of supershells at other wavelengths, including H i, far-infrared, soft X-ray, and SNRs. The implications of these findings are discussed in terms of the impact of supershells on star formation in the Galaxy.