{
  "id": "2010.02757",
  "version": "v1",
  "published": "2020-10-06T14:21:38.000Z",
  "updated": "2020-10-06T14:21:38.000Z",
  "title": "Structure and kinematics of shocked gas in Sgr B2: further evidence of a cloud-cloud collision from SiO emission maps",
  "authors": [
    "Jairo Armijos-Abendaño",
    "Wladimir Banda-Barragán",
    "Jesús Martín-Pintado",
    "Helga Dénes",
    "Christoph Federrath",
    "Miguel A. Requena-Torres"
  ],
  "comment": "Accepted for publication in MNRAS. 22 pages, 17 figures. Movies of the simulations can be found here: https://tinyurl.com/y5bc3smn",
  "categories": [
    "astro-ph.GA"
  ],
  "abstract": "We present SiO J=2-1 maps of the Sgr B2 molecular cloud, which show shocked gas with a turbulent substructure comprising at least three cavities at velocities of [10,40] km s$^{-1}$ and an arc at velocities of [-20,10] km s$^{-1}$. The spatial anti-correlation of shocked gas at low and high velocities, and the presence of bridging features in position-velocity diagrams suggest that these structures formed in a cloud-cloud collision. Some of the known compact HII regions spatially overlap with sites of strong SiO emission at velocities of [40,85] km s$^{-1}$, and are between or along the edges of SiO gas features at [100,120] km s$^{-1}$, suggesting that the stars responsible for ionizing the compact HII regions formed in compressed gas due to this collision. We find gas densities and kinetic temperatures of the order of $n_{\\rm H_2}\\sim 10^5\\rm cm^{-3}$ and $\\sim$30 K, respectively, towards three positions of Sgr B2. The average values of the SiO relative abundances, integrated line intensities, and line widths are $\\sim$10$^{-9}$, $\\sim$11 K km s$^{-1}$, and $\\sim$31 km s$^{-1}$, respectively. These values agree with those obtained with chemical models that mimic grain sputtering by C-type shocks. A comparison of our observations with hydrodynamical simulations shows that a cloud-cloud collision that took place $\\lesssim$ 0.5 Myr ago can explain the density distribution with a mean column density of $\\bar{N}_{\\rm H_2}\\gtrsim 5\\times10^{22}$ cm$^{-2}$, and the morphology and kinematics of shocked gas in different velocity channels. Colliding clouds are efficient at producing internal shocks with velocities $\\sim$5-50 km $s^{-1}$. High-velocity shocks are produced during the early stages of the collision and can readily ignite star formation, while moderate- and low-velocity shocks are important over longer timescales and can explain the widespread SiO emission in Sgr B2.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2020-10-06T14:21:38.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "shocked gas",
      "sio emission maps",
      "cloud-cloud collision",
      "kinematics",
      "sgr b2 molecular cloud"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 22,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}