Millimeter-wave CO and SiO Observations toward the Broad-velocity-width Molecular Feature CO 16.134–0.553: A Smith Cloud Scenario?

We report the results of the CO J = 1–0 and SiO J = 2–1 mapping observations toward the broad-velocity-width molecular feature (BVF) CO 16.134–0.553 with the Nobeyama Radio Observatory 45 m telescope. The high-quality CO map shows that the 5 pc size BVF bridges two separate velocity components at V _LSR ≃ 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 × 10² L _⊙, whereas no apparent driving sources were identified. Prominent SiO emission was detected from the BVF and its root in the V _LSR ≃ 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. A 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.