Millimeter-wave CO and SiO Observations toward the Broad-velocity-width Molecular Feature CO 16.134-0.553: a Smith cloud scenario?

Abstract

We report the results of the CO $\text{J}$=1-0 and SiO $\text{J}$=2-1 mapping observations towards the broad-velocity-width molecular feature CO 16.134-0.553 with the Nobeyama Radio Observatory 45 m telescope. The high quality CO map shows that the 5-pc size broad-velocity-width feature bridges two separate velocity components at ${\text{V}}_{\mathrm{LSR}}$$\simeq$ 40 km s${}^{-1}$ and 65 km s${}^{-1}$ in the position-velocity space. The kinetic power of CO 16.134-0.553 amounts to $7.8\times 10^2$ $\text{L}$${}_{\odot }$ whereas no apparent driving sources were identified. Prominent SiO emission was detected from the broad-velocity-width feature and its root in the ${\text{V}}_{\mathrm{LSR}}$$\simeq$ 40 km s${}^{-1}$ component. In the CO Galactic plane survey data, CO 16.134-0.553 appears to correspond to the Galactic eastern rim of a 15-pc diameter expanding CO shell. An $1°$-diameter H I emission void and $4°$-long vertical H I filament were also found above and below the CO shell, respectively. We propose that the high-velocity plunge of a dark matter subhalo with a clump of baryonic matter was responsible for the formation of the H I void, CO 16.134-0.553/CO shell, and the H I filament.

7 pages, 6 figures, 2 table, accepted for publication in ApJ

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