{
  "id": "1909.04641",
  "version": "v1",
  "published": "2019-09-10T17:33:21.000Z",
  "updated": "2019-09-10T17:33:21.000Z",
  "title": "Constraining structure formation using EDGES",
  "authors": [
    "Matteo Leo",
    "Tom Theuns",
    "Carlton M. Baugh",
    "Baojiu Li",
    "Silvia Pascoli"
  ],
  "comment": "19 pages, 3 figures. Prepared for submission to JCAP",
  "categories": [
    "astro-ph.CO"
  ],
  "abstract": "The experiment to detect the global epoch of reionization signature (EDGES) collaboration reported the detection of a line at 78~MHz in the sky-averaged spectrum due to neutral hydrogen (HI) 21-cm hyperfine absorption of cosmic microwave background photons at redshift $z\\sim17$. This requires that the spin temperature of HI be coupled to the kinetic temperature of the gas at this redshift through scattering of Lyman-$\\alpha$ photons emitted by massive stars. To explain the experimental result, star-formation needs to be sufficiently efficient at $z\\sim17$ and this can be used to constrain models in which small-scale structure formation is suppressed (DMF), either due to dark matter free-streaming or non-standard inflationary dynamics. We combine simulations of structure formation with a simple recipe for star-formation to investigate whether these models emit enough Lyman-$\\alpha$ photons to reproduce the experimental signal for reasonable values of the star-formation efficiency, $f_\\star$. We find that a thermal warm dark matter (WDM) model with mass $m_\\mathrm{WDM}\\sim4.3\\,\\mathrm{keV}$ is consistent with the timing of the signal for $f_\\star \\lesssim 2\\%$. The exponential growth of structure around $z\\sim 17$ in such a model naturally generates a sharp onset of the absorption. A model with $m_\\mathrm{WDM}\\sim3\\,\\mathrm{keV}$ requires higher star-formation efficiency, $f_\\star\\sim6\\%$, which is a factor of few above predictions of current star-formation models and observations of satellites in the Milky Way. However, uncertainties in the process of star-formation at these redshifts do not allow to derive strong constrains on such models using 21-cm absorption line. The onset of the 21-cm absorption is generally slower in DMF than in cold dark matter models, unless some process significantly suppresses star formation in halos with circular velocity below $\\sim 20$~km~s$^{-1}$.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2019-09-10T17:33:21.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "constraining structure formation",
      "absorption",
      "thermal warm dark matter",
      "cosmic microwave background photons",
      "cold dark matter models"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 19,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}