Radio-Selected Quasars in the Sloan Digital Sky Survey

TL;DR

This study combines radio and optical data from SDSS and FIRST to identify high-redshift quasars, revealing a higher fraction of reddened quasars and deriving a consistent radio-loud quasar luminosity function.

Contribution

It introduces a radio-selected quasar survey that reduces color bias and improves discovery rates for high-redshift quasars compared to optical methods.

Findings

29 quasars identified with 0.37 < z < 5.2

7 quasars with z > 3.5

Radio-selected quasars show higher reddening fraction

Abstract

We have conducted a pilot survey for z>3.5 quasars by combining the FIRST radio survey with the SDSS. While SDSS already targets FIRST sources for spectroscopy as quasar candidates, our survey includes fainter quasars and greatly improves the discovery rate by using strict astrometric criteria for matching the radio and optical positions. Our method allows for selection of high-redshift quasars with less color bias than with optical selection, as using radio selection essentially eliminates stellar contamination. We report the results of spectroscopy for 45 candidates, including 29 quasars in the range 0.37 < z < 5.2, with 7 having redshifts z>3.5. We compare quasars selected using radio and optical criteria, and find that radio-selected quasars have a much higher fraction of moderately-reddened objects. We derive a radio-loud quasar luminosity function at 3.5<z<4.0, and find that it is in good agreement with expectations from prior SDSS results.