Properties of radio-loud quasars in Sloan Digital Sky Survey

TL;DR

This study analyzes the spectral properties of 223 radio-loud quasars at low redshift, focusing on emission line features and their relation to black hole mass and galaxy dynamics, revealing deviations from the established M-sigma relation.

Contribution

It provides new insights into the spectral line characteristics and black hole mass relations of radio-loud quasars at low redshift, including the analysis of blue wings, outliers, and the M-sigma relation.

Findings

Most quasars show blue wings with velocities up to 420 km/s.

17% of quasars exhibit outliers with velocities between 419 and -315 km/s.

Radio-loud quasars generally do not follow the M-sigma relation, with an offset of 0.12 dex, increasing at higher redshifts.

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 fifty-four 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 towards lower wavelengths) and blue outliers (shift of the whole spectroscopic feature). Most of the quasars show blue wings with velocities up to 420 km $s^{-1}$. We find that around 17\% of the quasars show outliers with velocities spanning 419 to -315 km $s^{-1}$. Finally, we revisit the $\it M_{\rm BH} - \sigma$ relation of our sample using [S II]$\lambda$6716, 6731 and [O III] linewidths as surrogates for stellar velocity dispersions, $\sigma$, to investigate their location on the $\it M_{\rm BH} - \sigma$ relation for quiescent galaxies. Due to the strong blending of [S II] with $\rm H_{\alpha}$, we could estimate $\sigma_{[\rm SII]}$ of only 123 quasars. We find that the radio-loud quasars do not show a relationship between $\it M_{\rm BH}$ and $\sigma_{\rm [SII]/[OIII]}$ up to a redshift of 0.3, although they cluster around the local relation. We find an overall offset of 0.12$\pm$0.05 dex of our sample of radio-loud quasars from the $\it M_{\rm BH} - \sigma$ relation of quiescent galaxies. Quasars in our highest redshift bin (z=0.25-0.3) show a deviation of $\sim$0.33 $\pm$ 0.06 dex with respect to the local relation.