{
  "id": "1811.03107",
  "version": "v1",
  "published": "2018-11-07T19:00:06.000Z",
  "updated": "2018-11-07T19:00:06.000Z",
  "title": "The Evolution of Molecular Gas Fraction Traced by the CO Tully-Fisher Relation",
  "authors": [
    "Jacob W. Isbell",
    "Rui Xue",
    "Hai Fu"
  ],
  "comment": "8 pages, 3 figures, 1 table. Submitted to ApJ Letters",
  "categories": [
    "astro-ph.GA"
  ],
  "abstract": "Carbon monoxide (CO) observations show a luminosity$-$line-width correlation that evolves with redshift. We present a method to use CO measurements alone to infer the molecular gas fraction ($f_{\\rm mol}$) and constrain the CO$-$H$_2$ conversion factor ($\\alpha_{\\rm CO}$). We compile from the literature spatially integrated low-$J$ CO observations of six galaxy populations, including a total of 480 galaxies between $0.01 \\leq z \\leq 3.26$. The CO data of each population provide an estimate of the $\\alpha_{\\rm CO}$-normalized mean molecular gas fraction ($f_{\\rm mol}/\\alpha_{\\rm CO}$). The redshift evolution of the luminosity$-$line-width correlation thus indicates an evolution of $f_{\\rm mol}/\\alpha_{\\rm CO}$. We use a Bayesian-based Monte-Carlo Markov Chain sampler to derive the posterior probability distribution functions of $f_{\\rm mol}/\\alpha_{\\rm CO}$ for these galaxy populations, accounting for random inclination angles and measurement errors in the likelihood function. We find that the molecular gas fraction evolves rapidly with redshift, $f_{\\rm mol} \\propto (1+z)^\\beta$ with $\\beta \\simeq 2$, for both normal star-forming and starburst galaxies. Furthermore, the evolution trend agrees well with that inferred from the Kennicutt-Schmidt law and the star-forming main sequence. Finally, at $z < 0.1$ normal star-forming galaxies require a $\\sim5\\times$ larger $\\alpha_{\\rm CO}$ than starburst galaxies to match their molecular gas fractions, but at $z > 1$ both star-forming types exhibit sub-Galactic $\\alpha_{\\rm CO}$ values and normal star-forming galaxies appear more gas-rich than starbursts. Future applications of this method include calibrating Tully-Fisher relations without inclination correction and inferring the evolution of the atomic gas fraction with HI observations.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2018-11-07T19:00:06.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "tully-fisher relation",
      "mean molecular gas fraction",
      "gas fraction evolves",
      "normal star-forming galaxies",
      "posterior probability distribution functions"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 8,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}