Redshifts of Candidate Gamma-Ray Blazars

We identify 16 optical counterparts of blazars that have been suggested as sources of high-energy gamma-ray emission detected by the EGRET instrument on board the Compton Gamma-Ray Observatory. Nine new redshifts are obtained, as well one contradiction and two confirmations of published redshifts ranging from z = 0.566 to z = 3.00. The optical spectra of four objects are featureless, including high signal-to-noise spectra of the likely counterparts of 3EG J0433+2908 and GeV J0508+0540, which, if at low redshift, would be attractive targets to search for TeV emission using atmospheric Cerenkov telescopes, because they emit above 10 GeV. However, the combination of spectroscopy and CCD imaging of those objects shows no evidence for their underlying host galaxies, which probably means that z > 0.3, diminishing their prospects as TeV sources.

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