{
  "id": "2010.02944",
  "version": "v1",
  "published": "2020-10-06T18:00:15.000Z",
  "updated": "2020-10-06T18:00:15.000Z",
  "title": "Morphological and Rotation Structures of Circumgalactic Mg II Gas in the EAGLE Simulation and the Dependence on Galaxy Properties",
  "authors": [
    "Stephanie H. Ho",
    "Crystal L. Martin",
    "Joop Schaye"
  ],
  "comment": "26 pages with 18 figures and 3 tables; accepted for publication in ApJ",
  "categories": [
    "astro-ph.GA"
  ],
  "abstract": "Low-ionization-state Mg II gas has been extensively studied in quasar sightline observations to understand the cool, $\\sim$$10^4$ K gas in the circumgalactic medium. Motivated by recent observations showing that the Mg II gas around low-redshift galaxies has significant angular momentum, we use the high-resolution EAGLE cosmological simulation to analyze the morphological and rotation structures of the $z\\approx0.3$ circumgalactic Mg II gas and examine how they change with the host galaxy properties. Around star-forming galaxies, we find that the Mg II gas has an axisymmetric instead of a spherical distribution, and the axis of symmetry aligns with that of the Mg II gas rotation. A similar rotating structure is less commonly found in the small sample of simulated quiescent galaxies. We also examine how often Mg II gas around galaxies selected using a line-of-sight velocity cut includes gas physically outside of the virial radius ($r_\\mathrm{vir}$). For example, we show that at an impact parameter of 100 pkpc, a $\\pm500$ km s$^{-1}$ velocity cut around galaxies with stellar masses of $10^9$-$10^{9.5}\\mathrm{M_\\odot}$ ($10^{10}$-$10^{10.5}\\mathrm{M_\\odot}$) selects Mg II gas beyond the virial radius 80% (6%) of the time. Because observers typically select Mg II gas around target galaxies using such a velocity cut, we discuss how this issue affects the study of circumgalactic Mg II gas properties, including the detection of corotation. While the corotating Mg II gas generally extends beyond $0.5r_\\mathrm{vir}$, the Mg II gas outside of the virial radius contaminates the corotation signal and makes observers less likely to conclude that gas at large impact parameters (e.g., $\\gtrsim0.25 r_\\mathrm{vir}$) is corotating.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2020-10-06T18:00:15.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "galaxy properties",
      "circumgalactic mg",
      "rotation structures",
      "eagle simulation",
      "dependence"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 26,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}