The black hole mass, Eddington ratio and MBH-σ[OIII] relation in young radio galaxies

The masses of the central supermassive black holes (BHs) and the Eddington ratios for a sample of 65 young radio galaxies [27 gigahertz-peaked spectrum (GPS) and 38 compact steep-spectrum (CSS) sources] are estimated by various methods. We find that the average BH mass of these young radio galaxies is <logM_BH> ~= 8.3, which is less than that of radio loud quasi-stellar objects (QSOs) and low-redshift radio galaxies (<logM_BH> ~= 9.0). The CSS/GPS sources have relatively high Eddington ratios with average ratio <logL_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-σ_* relation defined by nearby inactive galaxies, when using σ_[OIII as a surrogate for the stellar velocity dispersion σ_*. There is no significant correlation between the deviation of the [OIII] emission line width, Δσ ≡ σ_[OIII] - σ_[pred] and the jet/accretion power, where σ_[pred] are calculated from the Tremaine et al. relation using the estimated BH masses. However, we find that the deviation Δσ in young radio galaxies is well correlated with the Eddington ratio, and this correlation is found to be similar to that of radio quiet active galactic nuclei (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 [OIII] narrow line in these young radio galaxies.