Spectroscopy of Ultra--Steep Spectrum Radio Sources: A Sample of z>2 Radio Galaxies

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dc.creatorRöttgering, H. J. A.
dc.creatorvan Ojik, R.
dc.creatorMiley, G. K.
dc.creatorChambers, K. C.
dc.creatorvan Breugel, W. J. M.
dc.creatorde Koff, S.
dc.date1996-08-12
dc.date.accessioned2026-07-07T02:21:44Z
dc.date.available2026-07-07T02:21:44Z
dc.descriptionWe 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 ($α< -1$) 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$α$ is almost always the dominant emission line, with a rest frame equivalent width ranging from $\sim100$ Å to more than 1000 Å. The equivalent widths of the most important emission lines (Ly$α$, 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$α$ 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$α$ emission line may be
dc.descriptionAccepted for publication in Astronomy and Astrophysics
dc.identifierhttps://arxiv.org/abs/astro-ph/9608063
dc.identifierhttp://arxiv.org/abs/astro-ph/9608063
dc.identifier.urihttp://salesiana.dossiersoluciones.com/handle/123456789/10615
dc.subjectAstrophysics
dc.titleSpectroscopy of Ultra--Steep Spectrum Radio Sources: A Sample of z>2 Radio Galaxies
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