Radio-Selected Quasars in the Sloan Digital Sky Survey

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.

15 pages, 11 figures, accepted for publication in AJ

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• Constraining the radio-loud fraction of quasars at z>5.5
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• The radio spectral turnover of radio-loud quasars at $z>5$
• Observations by GMRT at 323 MHz of radio-loud quasars at $z>5$
• Neural-network selection of high-redshift radio quasars, and the luminosity function at z~4
• High-$z$ radio Quasars in RACS I: Selection, identification, and multi-wavelength properties
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• The optical luminosity function of LOFAR radio-selected quasars at $1.4\le z\le 5.0$ in the NDWFS-Boötes field
• Revealing faint compact radio jets at redshifts above 5 with very long baseline interferometry
• Discovering bright quasars at intermediate redshifts based on the optical/near-IR colors