{
  "id": "astro-ph/0312550",
  "version": "v1",
  "published": "2003-12-19T23:40:55.000Z",
  "updated": "2003-12-19T23:40:55.000Z",
  "title": "A Disk Galaxy of Old Stars at z ~ 2.5",
  "authors": [
    "Alan Stockton",
    "Gabriela Canalizo",
    "Toshinori Maihara"
  ],
  "comment": "8 pages, 6 figures, emulateapj.sty, accepted for publication in The Astrophysical Journal",
  "journal": "Astrophys.J. 605 (2004) 37-44",
  "doi": "10.1086/382235",
  "categories": [
    "astro-ph"
  ],
  "abstract": "We describe observations of a galaxy in the field of the $z=2.483$ radio galaxy 4C 23.56, photometrically selected to have a spectral-energy distribution consistent with an old stellar population at the redshift of the radio galaxy. Exploration of redshift--stellar-population-reddening constraints from the photometry indicates that the galaxy is indeed at a redshift close to that of 4C23.56, that the age of the most recent significant star formation is roughly >~2 Gyr, and that reddening is fairly modest, with more reddening required for the younger end of stellar age range. From analysis of a deep adaptive-optics image of the galaxy, we find that an r^1/4-law profile, common for local spheroidal galaxies, can be excluded quite strongly. On the other hand, a pure exponential profile fits remarkably well, while the best fit is given by a Sersic profile with index n=1.49. Reconstruction of the two-dimensional form of the galaxy from the best-fit model is consistent with a disk galaxy with neither a significant bulge component nor gross azimuthal structure. The assembly of roughly 2L* of old stars into such a configuration this early in the history of the universe is not easily explainable by any of the currently popular scenarios for galaxy formation. A galaxy with these properties would seem to require smooth but rapid infall of the large mass of gas involved, followed by a burst of extremely vigorous and efficient star formation in the resulting disk.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2003-12-19T23:40:55.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "old stars",
      "disk galaxy",
      "exponential profile fits remarkably",
      "significant star formation",
      "radio galaxy 4c"
    ],
    "tags": [
      "journal article"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 8,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 636167
    }
  }
}