{
  "id": "2106.14894",
  "version": "v1",
  "published": "2021-06-28T18:00:01.000Z",
  "updated": "2021-06-28T18:00:01.000Z",
  "title": "Towards a Better Understanding of Cosmic Chronometers: Stellar Population Properties of Passive Galaxies at Intermediate Redshift",
  "authors": [
    "Nicola Borghi",
    "Michele Moresco",
    "Andrea Cimatti",
    "Alexandre Huchet",
    "Salvatore Quai",
    "Lucia Pozzetti"
  ],
  "comment": "28 pages, 13 figures, 6 tables, submitted to ApJ",
  "categories": [
    "astro-ph.GA",
    "astro-ph.CO"
  ],
  "abstract": "We take advantage of the publicly available LEGA-C spectroscopic survey to measure the stellar population properties of 140 individual massive and passive galaxies at $z\\sim0.7$. We develop and publicly release PyLick, a flexible python code to measure UV to near-IR spectral indices. With PyLick we study the H/K ratio as a new diagnostic based on the pseudo-Lick CaII H and K indices, and find that a cut in ${\\rm H/K}<1.1$ can be used jointly with other criteria to select (or verify the purity of) samples of passive galaxies. By combining photometric and spectroscopic criteria, we select a reliable sample of passively evolving galaxies. We constrain single-burst stellar ages, metallicities $\\mathrm{[Z/H]}$, and $\\mathrm{[\\alpha/Fe]}$ with an optimized set of Lick indices, exploring in detail the robustness of our measurement against different combinations. Even without imposing cosmological priors, the derived ages follow a clear trend compatible with the expected cosmological aging of the Universe. We observe no significant redshift evolution for the metal abundance with respect to the values derived at $z=0$, with median $\\mathrm{[Z/H]}=0.08\\pm0.18$ and $\\mathrm{[\\alpha/Fe]}=0.13\\pm0.11$. Finally, we find positive correlations between $\\log\\mathrm{age}$, $\\mathrm{[Z/H]}$, $\\mathrm{[\\alpha/Fe]}$ and the stellar velocity dispersion, with slopes of ($0.48\\pm0.14$), ($0.26\\pm0.17$), and ($0.23\\pm0.11$), respectively; the small scatter of $<0.2$ dex points to rather homogeneous and short star formation histories. Overall, these results confirm and extend low-redshift findings of a mass-downsizing evolution. This work further strengthens the possibility of selecting pure samples of passive galaxies to be exploited reliably as cosmic chronometers to place independent cosmological constraints.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2021-06-28T18:00:01.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "stellar population properties",
      "passive galaxies",
      "cosmic chronometers",
      "intermediate redshift",
      "better understanding"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 28,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}