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

Abstract

We present optical identifications and redshifts for seventeen new high-redshift radio sources. Fifteen of these sources are radio galaxies; the remaining two are high-redshift, steep-spectrum, radio-loud quasars. These objects were discovered as part of an ongoing study of compact (theta < 10 arcsec), 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) > 50 mJy). Spectra for the optical counterparts were obtained at the W.M. Keck Telescopes and are among the optically faintest radio galaxies thus far identified. Redshifts range between 0.3 and 3.6, with thirteen of the seventeen at redshifts greater than 1.5. Combining these new radio galaxies with two published MG radio galaxy spectra, we synthesize a composite MG radio galaxy spectrum and discuss the properties of these galaxies in comparison to other, more powerful, radio galaxies at similar redshifts. We suggest a radio power-ionization state relation.