An energetic high-velocity compact cloud: CO−0.31+0.11

Abstract

ABSTRACT 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 (ΔV > 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 $10^{4}\, M_{\odot }$ 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 $2\times 10^{5}\, M_\odot$. 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.