{
  "id": "1706.04613",
  "version": "v1",
  "published": "2017-06-14T18:00:00.000Z",
  "updated": "2017-06-14T18:00:00.000Z",
  "title": "HST imaging of the brightest z~8-9 galaxies from UltraVISTA: the extreme bright end of the UV luminosity function",
  "authors": [
    "Mauro Stefanon",
    "Ivo Labbé",
    "Rychard J. Bouwens",
    "Gabriel B. Brammer",
    "Pascal Oesch",
    "Marijn Franx",
    "Johan P. U. Fynbo",
    "Bo Milvang-Jensen",
    "Adam Muzzin",
    "Garth D. Illingworth",
    "Olivier Le Fèvre",
    "Karina I. Caputi",
    "Benne W. Holwerda",
    "Henry J. McCracken",
    "Renske Smit",
    "Dan Magee"
  ],
  "comment": "20 pages, 8 figures. Submitted to ApJ. Comments welcome",
  "categories": [
    "astro-ph.GA"
  ],
  "abstract": "We report on the discovery of three especially bright candidate $z_{phot} \\gtrsim 8$ galaxies. Five sources were targeted for follow-up with HST/WFC3, selected from a larger sample of 16 bright ($24.8 \\lesssim H\\lesssim25.5$~mag) candidate $z\\gtrsim 8$ LBGs identified over the 1.6 degrees$^2$ of the COSMOS/UltraVISTA field. These were identified as $Y$ and $J$ dropouts by leveraging the deep ($Y$-to-$K_\\mathrm{S} \\sim 25.6-25.2$~mag, $5\\sigma$) NIR data from the UltraVISTA DR3 release, deep ground based optical imaging from the CFHTLS and Subaru Suprime Cam programs and Spitzer/IRAC mosaics combining observations from the SMUVS and SPLASH programs. Through the refined spectral energy distributions, which now also include new HyperSuprime Cam $g, r, i, z,$ and $Y$ band data, we confirm that 3/5 galaxies have robust $z_{phot}\\sim8.0-8.7$, consistent with the initial selection. The remaining 2/5 galaxies have a nominal $z_{phot}\\sim2$. However, if we use the HST data alone, these objects have increased probability of being at $z\\sim9$. Furthermore, we measure mean UV continuum slopes $\\beta=-1.97\\pm0.23$ for the three $z\\sim8-9$ galaxies, marginally bluer than similarly luminous $z\\sim4-6$ in CANDELS but consistent with previous measurements of similarly luminous galaxies at $z \\sim 7$. The circularized effective radius for our brightest source is $0.9\\pm0.2$ kpc, consistent with previous measurements for a bright $z\\sim11$ galaxy and bright $z\\sim7$ galaxies. Finally, using the $1/V_\\mathrm{max}$ formalism, we estimate for the first time the volume density of the extreme bright ($M_\\mathrm{UV}\\lesssim -22$~mag) end of the $z\\sim8$ UV LF from actual detection of sources, as opposed to current upper limits from non-detections. Despite this exceptional result, the still large statistical uncertainties do not allow us to discriminate between a Schechter and a double power-law form.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2017-06-14T18:00:00.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "uv luminosity function",
      "extreme bright end",
      "hst imaging",
      "measure mean uv continuum slopes",
      "ultravista"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 20,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}