NASA/IPAC EXTRAGALACTIC DATABASE
Date and Time of the Query: 2019-06-25 T01:36:39 PDT
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For refcode 1997A&A...326..505R:
Retrieve 64 NED objects in this reference.
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Copyright by European Southern Observatory (ESO). Reproduced by permission
1997A&A...326..505R Spectroscopy of ultra-steep spectrum radio sources: a sample of z>2 radio galaxies. Roettgering H.J.A., van Ojik R., Miley G.K., Chambers K.C., van Breugel W.J.M., de Koff S. Received 12 December 1995/Accepted 22 July 1996 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 ~100 A to more than 1000 A. The equivalent widths of the most important emission lines (Ly{alpha}, C IV, He II, C 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 in some cases. Simulations show that the effects of associated H I absorption on the Ly{alpha} emission line may be responsible for most of these velocity shifts. However, other mechanisms such as organized kinematics of the Ly{alpha} emission line gas (e.g. inflow or outflow) and obscuration of the line emission from the far side of the radio galaxy may also play a role. Key words: galaxies: active - galaxies: redshifts - galaxies: ISM - radio continuum: galaxies
Retrieve 64 NED objects in this reference.
Please click here for ADS abstract

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