New High-Redshift Radio Galaxies from the MIT–Green Bank Catalog

We present optical identifications and redshifts for seventeen newhigh-redshift radio sources. Fifteen of these sources are radio galaxies; theremaining two are high-redshift, steep-spectrum, radio-loud quasars. Theseobjects were discovered as part of an ongoing study of compact (theta < 10arcsec), moderately steep spectrum (alpha(1.4 GHz;4.8 GHz) > 0.75, S(nu) ~nu^(-alpha)) sources from the MIT-Green Bank (MG) radio catalog (S(5 GHz) > 50mJy). Spectra for the optical counterparts were obtained at the W.M. KeckTelescopes and are among the optically faintest radio galaxies thus faridentified. Redshifts range between 0.3 and 3.6, with thirteen of the seventeenat redshifts greater than 1.5. Combining these new radio galaxies with twopublished MG radio galaxy spectra, we synthesize a composite MG radio galaxyspectrum and discuss the properties of these galaxies in comparison to other,more powerful, radio galaxies at similar redshifts. We suggest a radiopower-ionization state relation.Comment: 35 pages, 5 figures; accepted to the Astronomical Journal (March 1999