{
  "id": "2008.08092",
  "version": "v1",
  "published": "2020-08-18T18:00:02.000Z",
  "updated": "2020-08-18T18:00:02.000Z",
  "title": "CGM$^{2}$ I: The Extent of the Circumgalactic Medium Traced by Neutral Hydrogen",
  "authors": [
    "Matthew C. Wilde",
    "Jessica K. Werk",
    "Joseph N. Burchett",
    "J. Xavier Prochaska",
    "Kirill Tchernyshyov",
    "Todd M. Tripp",
    "Nicolas Tejos",
    "Nicolas Lehner",
    "Rongmon Bordoloi",
    "John M. O'Meara",
    "Jason Tumlinson"
  ],
  "comment": "27 pages, 14 figures. Submitted to ApJ, Comments welcome",
  "categories": [
    "astro-ph.GA"
  ],
  "abstract": "We present initial results from the COS and Gemini Mapping the Circumgalactic Medium (CGMCGM $\\equiv$ CGM$^{2}$) survey. The CGM$^{2}$ spectroscopic survey consists of 1689 galaxies, all with high-quality Gemini GMOS spectra suitable for precise redshift measurements, within 1 Mpc of twenty-two $z \\lesssim 1$ quasars, all with existing S/N$\\sim$10 HST-COS G130M$+$G160M spectra. We show that the HI covering fraction above a threshold of $N_{\\rm HI}$ $>10^{14} $cm$^{-2}$ is $\\gtrsim 0.6$ within 1.5 virial radii ($R_{\\rm vir} \\sim R_{200m}$) of galaxies having stellar masses $10^{8} M_{\\odot} < M_{\\star} < 10^{11} M_{\\odot}$. We examine the kinematics of the HI absorption relative to the galaxy systemic velocities and find that the majority of absorption lies within $\\pm$ 250 km s$^{-1}$, and that this concentration increases with increasing HI column density from $N_{\\rm HI}$ $=10^{14} - 10^{17}$ cm$^{-2}$. We examine HI covering fractions over a range of impact parameters to infer a characteristic size of the CGM, $R^{14}_{\\rm CGM}$, as a function of galaxy mass. $R^{14}_{\\rm CGM}$ is the impact parameter at which the probability of observing an absorber with $N_{\\rm HI}$ $>$ 10$^{14}$ cm$^{-2}$ is $>$ 50%. In this framework, the radial extent of the CGM of $M_{\\star} > 10^{10} M_{\\odot}$ galaxies is $R^{14}_{\\rm CGM} = 362_{-72}^{+83}$ kpc or $R^{14}_{\\rm CGM} = 1.4R_{\\rm vir}$. Lower-mass galaxies show a smaller physical scale $R^{14}_{\\rm CGM} = 281_{-36}^{+42}$ kpc but extend to $R^{14}_{\\rm CGM} = 2.3R_{\\rm vir}$. Our analysis suggests that using $R_{\\rm vir}$ as a proxy for the characteristic radius of the CGM likely underestimates its extent, especially for galaxies with $M_{\\star} < 10^{10} M_{\\odot}$.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2020-08-18T18:00:02.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "circumgalactic medium",
      "neutral hydrogen",
      "hi covering fraction",
      "impact parameter",
      "precise redshift measurements"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 27,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}