An Energetic High-velocity Compact Cloud CO–0.31+0.11

We have discovered an energetic high-velocity compact cloud CO–0.31+0.11 in the central molecular zone of our Galaxy. CO–0.31+0.11 is located at a projected distance of ∼ 45 pc from the Galactic nucleus Sgr A^∗. It is characterized by its compact spatial appearance (d ≃ 4 pc), extremely broad velocity width (∆V > 100 km s⁻¹), and high CO J=3–2/J=1–0 intensity ratio. The total gas mass and kinetic energy are estimated as approximately 10⁴ M_☉ and 10⁵¹ erg, respectively. Two expanding bubble-like structures are found in our HCN J=1–0 map obtained with the Nobeyama Radio Observatory 45 m telescope. In the longitude–velocity maps, CO–0.31+0.11 exhibits an asymmetric V-shape. This kinematical structure can be well fitted by Keplerian motion on an eccentric orbit around a point mass of 2 × 10⁵ M_☉. The enhanced CO J=3–2/J=1–0 ratio is possibly attributed to the tidal compression during the pericenter passage. The model suggests that a huge mass is packed within a radius of r < 0.1 pc. The huge mass, compactness and absence of luminous stellar counterparts may correspond to a signature of an intermediate-mass black hole (IMBH) inside. We propose a formation scenario of CO–0.31+0.11 in which a compact cloud has gravitationally interacted with an IMBH and a bipolar molecular outflow was driven by the past activity of the putative IMBH.