{
  "id": "astro-ph/9608063",
  "version": "v1",
  "published": "1996-08-12T10:57:06.000Z",
  "updated": "1996-08-12T10:57:06.000Z",
  "title": "Spectroscopy of Ultra--Steep Spectrum Radio Sources: A Sample of z>2 Radio Galaxies",
  "authors": [
    "H. J. A. Röttgering",
    "R. van Ojik",
    "G. K. Miley",
    "K. C. Chambers",
    "W. J. M. van Breugel",
    "S. de Koff"
  ],
  "comment": "Accepted for publication in Astronomy and Astrophysics",
  "categories": [
    "astro-ph"
  ],
  "abstract": "We present spectroscopic observations for 64 radio galaxies having ultra steep radio spectra. Twenty-nine objects have redshifts $z>2$, the largest redshifts being almost 4. Our ultra steep spectrum (USS) criterion ($\\alpha < -1$) has proven to be the most efficient way of finding distant radio galaxies. We find that even among the USS sources, there is a strong statistical correlation between the spectral index and redshift. The most distant radio galaxies within the USS sample have the steepest radio spectra. In our sample there are 3 radio galaxies at $z>3$ compared with 26 at $2 < z < 3$. However, the present data do not allow us to decide whether there is a decrease in co-moving source density at the highest redshifts. We have analyzed the spectra of the 30 objects with the highest redshifts ($z>1.9$). For these high redshift radio galaxies, Ly$\\alpha$ is almost always the dominant emission line, with a rest frame equivalent width ranging from $\\sim100$ \\AA\\ to more than 1000 \\AA. The equivalent widths of the most important emission lines (Ly$\\alpha$, C\\,{\\small IV}, He\\,{\\small II}, C\\,{\\small III}]) are found to correlate strongly with each other. The large rest frame equivalent widths and the correlation between the equivalent widths of the emission lines, confirm that photoionization by a central continuum source is most likely the dominant ionization mechanism. There are significant velocity differences between the various emission lines of our high redshift radio galaxies; in particular the Ly$\\alpha$ line is shifted with respect to the higher ionization lines. Velocity shifts range from 100 to almost 1000 km s$^{-1}$ in some cases. Simulations show that the effects of associated H\\,{\\small I} absorption on the Ly$\\alpha$ emission line may be",
  "revisions": [
    {
      "version": "v1",
      "updated": "1996-08-12T10:57:06.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "ultra-steep spectrum radio sources",
      "rest frame equivalent width",
      "emission line",
      "high redshift radio galaxies",
      "distant radio galaxies"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 0,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 436461
    }
  }
}