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

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.

Discovery of a Giant Molecular Loop in the Central Region of NGC 253

“…An IMBH gravitationally attracts the ambient gas, which circulates in the Kepler orbit around the IMBH and creates molecular gas having large velocity dispersion. Takekawa et al (2019) proposed that the molecular gas around an IMBH having ∼10 5 M e mass has mass of ∼10 4 M e , with the radius of ∼5 pc, showing velocity width of 100 km s −1 . So if there is a group of IMBHs, a high-velocity, larger-sized cloud is represented.…”

“…The compactness and relatively higher energy of an HVCC cannot be explained by a SNe, and then the origin of them might be related to the gas dynamics of CMZs in galaxies. The origin of an HVCC is considered to be a multiple SNe (e.g., Tanaka et al 2007), a Cloud-Cloud Collision (e.g., Sormani et al 2019;Enokiya et al 2021b), and an IMBH (Oka et al 2016;Takekawa et al 2019). The HVCCs found in the present study are limited in space and thus we still do not discuss the connection between HVCCs and gas dynamics of the CMZ of NGC 253.…”

Catalog of High-velocity Dispersion Compact Clouds in the Central Molecular Zone of Our Galaxy

“…CO-0.40-0.22 (originally CO-0.41-0.23 in Oka et al 2007 is the first example of such a gravitationally kicked HVDCC, which may harbor an intermediate-mass black hole (IMBH) with a mass of 10 5 M ☉ (Oka et al 2016(Oka et al , 2017. Subsequently, HCN-0.009-0.044 (Takekawa et al 2017(Takekawa et al , 2019a, CO-0.31+0.11 (Takekawa et al 2019b), and HCN-0.085-0.094 (Takekawa et al 2020) were considered as candidates for HVDCCs that include IMBHs. Compact broad-velocity-width features were also detected in the Galactic disk.…”

Discovery of a giant molecular loop in the central region of NGC 253

“…A IMBH attracts gravitationally the ambient gas, which circulates in the Kepler orbit around the IMBH and creates molecular gas having large velocity dispersion. Takekawa et al (2019) proposed that the molecular gas around a IMBH having ∼10 5 M mass has mass of ∼10 4 M , with the radius of ∼5 pc, showing velocity width of 100 km s −1 . The present loop has total mass of ∼10 7 M , suggesting that it may include 1000 IMBHs with the mass of ∼10 5 M , whereas their total mass amounts of IMBHs to ∼10 8 M .…”