{
  "id": "2109.10875",
  "version": "v1",
  "published": "2021-09-22T17:44:48.000Z",
  "updated": "2021-09-22T17:44:48.000Z",
  "title": "MUSE observations of the ionized gas in a galaxy group at z = 0.45 with 21-cm HI absorption towards PKS 1610-771",
  "authors": [
    "Simon Weng",
    "Elaine M. Sadler",
    "Caroline Foster",
    "Céline Peroux",
    "Elizabeth K. Mahony",
    "James R. Allison",
    "Vanessa A. Moss",
    "Renzhi Su",
    "Matthew T. Whiting",
    "Hyein Yoon"
  ],
  "comment": "13 pages, 8 figures",
  "categories": [
    "astro-ph.GA"
  ],
  "abstract": "We present results from MUSE observations following up on a 21-cm \\ion{H}{i} absorption system detected with the Australian Square Kilometre Array Pathfinder radio telescope at redshift $0.4503$ towards the quasar PKS 1610-771. This \\ion{H}{i} absorber has a column density $N_{HI} = 2.7 \\pm 0.1 \\times 10^{20} \\cdot \\rm{[T_{s}/100 K]} \\cdot \\rm{cm}^{-2}$, making it a likely Damped Lyman-$\\alpha$ (DLA) system. We identify a galaxy group with four members (A, B, X and Y) at the same redshift as the \\ion{H}{i} absorption system, with impact parameters ranging from less than 10\\,kpc to almost 200\\,kpc from the quasar sightline. \\ion{Ca}{ii} and \\ion{Na}{i} absorption is also seen in the MUSE spectrum of the background QSO, with velocities coinciding with the initial \\ion{H}{i} $21$-cm detection, but tracing less dense and potentially warmer gas. This metal-line component aligns with the rotating ionized disc of galaxy B (impact parameter $18$ kpc from the QSO) and appears to be co-rotating with the galaxy disc, although outflowing gas cannot be directly excluded. In contrast, the $21$-cm \\ion{H}{i} absorber is blueshifted relative to the galaxies nearest the absorber and has the opposite sign to the velocity field of galaxy B. Since galaxies A and B are separated by only $17$ kpc on the sky and $70$ km s$^{-1}$ in velocity, it is likely that the $21$-cm detection traces extragalactic clouds of gas formed from their interaction. This system represents a first case study of the cold gas detected in galaxy groups by future large $21$-cm absorption surveys, such as the First Large Absorption Survey in \\ion{H}{i}.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2021-09-22T17:44:48.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "galaxy group",
      "muse observations",
      "detection traces extragalactic clouds",
      "hi absorption",
      "array pathfinder radio telescope"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 13,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}