Properties of radio-loud quasars in the Sloan Digital Sky Survey

Abstract

We present a study of a sample of 223 radio-loud quasars (up to redshift < 0.3) in order to investigate their spectral properties. Twenty-six of these radio-loud quasars are identified as flat-spectrum radio quasars (FSRQs), and 54 are identified as steep-spectrum radio quasars (SSRQs) based on their radio spectral index. We study the [O III] line properties of these quasars to investigate the origin and properties of blue wings (shift of the profile toward lower wavelengths) and blue outliers (shift of the whole spectroscopic feature). Most of the quasars show blue wings with velocities of up to 420 km s−1. We find that about 17% of the quasars show outliers whose velocities span from 419 to −315 km s−1. Finally, we revisit the MBH − σ relation of our sample using the [S II]λ 6716,6731 and [O III] line widths as surrogates for stellar velocity dispersions, σ, to investigate their location on the MBH − σ relation for quiescent galaxies. Because [S II] is strongly blended with Hα, we were able to estimate σ[S II] for only 123 quasars. We find that the radio-loud quasars do not show a relationship between MBH and σ[S II]/[O III] up to a redshift of 0.3, although they cluster around the local relation. We find an overall offset of 0.12 ± 0.05 dex of our sample of radio-loud quasars from the MBH − σ relation of quiescent galaxies. Quasars in our highest redshift bin (z = 0.25 − 0.3) show a deviation of ∼0.33 ± 0.06 dex from the local relation. Implications of the results are discussed.