The black hole mass, Eddington ratio, and M_bh-\sigma_[O III] relation in young radio galaxies

TL;DR

This study estimates black hole masses and accretion rates in young radio galaxies, revealing their deviation from the standard M_bh-_* relation and suggesting accretion activity influences their narrow line region kinematics.

Contribution

It provides the first comprehensive analysis of black hole properties and [O III] line kinematics in young radio galaxies, highlighting the role of accretion in their emission line behavior.

Findings

Young radio galaxies have lower black hole masses than QSOs and radio galaxies.

Eddington ratios in CSS/GPS sources are similar to NLS1s, indicating early accretion activity.

Deviation in [O III] line width correlates with Eddington ratio, not jet power.

Abstract

The BH masses and the Eddington ratios for a sample of 65 young radio galaxies [27 GPS and 38 CSS sources] are estimated by various methods. We find that the average BH mass of these young radio galaxies is <log M_bh>=8.3, which is less than that of radio loud QSOs and low redshift radio galaxies(<log M_bh>=9.0). The CSS/GPS sources have relatively high Eddington ratios with average ratio <log L_bol/L_Edd>=-0.56, which are similar to those of narrow line Seyfert 1 galaxies (NLS1s). It suggests that the CSS/GPS sources may not only be in the early stage of radio activities, but also in the early stage of their accretion activities. We find that the young radio galaxies as a class deviate systematically from the M_bh-\sigma_* relation defined by nearby inactive galaxies, when using \sigma_[O III] as a surrogate for the stellar velocity dispersion \sigma_*. There is no significant correlation between the deviation of the [O III] emission line width, $\Delta\sigma$=\sigma_[O III]-\sigma_[pred], and the jet/accretion power, where \sigma_[pred] are calculated from the Tremaine et al. relation using the estimated BH masses. However, we find that the deviation $\Delta\sigma$ in young radio galaxies is well correlated with the Eddington ratio, and this correlation is found to be similar to that of radio quiet AGN (QSOs/NLS1s) where the radio jet is absent or weak. We suggest that the accretion activities may still play an important role in shaping the kinematics of [O III] narrow line in these young radio galaxies.