On the BL Lacertae objects/radio quasars and the FRI/II dichotomy

TL;DR

This paper supports the unification scheme of radio-loud AGNs by showing BL Lac objects and radio quasars are separated in the black hole mass-jet power plane, with different accretion modes indicated by their Eddington ratios.

Contribution

It translates the FR I/II dividing line into the black hole mass-jet power plane and demonstrates the separation of BL Lacs and quasars, supporting unification models.

Findings

BL Lac objects are separated from radio quasars in the M_bh-Q_jet plane.

BL Lac objects have systematically lower Eddington ratios than quasars.

Eddington ratio distribution is bimodal, indicating different accretion modes.

Abstract

In the frame of unification schemes for radio-loud active galactic nuclei (AGNs), FR I radio galaxies are believed to be BL Lacertae (BL Lac) objects with the relativistic jet misaligned to our line of sight, and FR II radio galaxies correspond to misaligned radio quasars. The Ledlow-Owen dividing line for FR I/FR II dichotomy in the optical absolute magnitude of host galaxy-radio luminosity (M_R-L_Rad) plane can be translated to the line in the black hole mass-jet power (M_bh-Q_jet) plane by using two empirical relations: Q_jet-L_Rad and M_bh}-M_R. We use a sample of radio quasars and BL Lac objects with measured black hole masses to explore the relation of the jet power with black hole mass, in which the jet power is estimated from the extended radio emission. It is found that the BL Lac objects are clearly separated from radio quasars by the Ledlow & Owen FR I/II dividing line in the M_bh-Q_jet plane. This strongly supports the unification schemes for FR I/BL Lac object and FR II/radio quasar. We find that the Eddington ratios L_bol/L_Edd of BL Lac objects are systematically lower than those of radio quasars in the sample with a rough division at L_bol/L_Edd 0.01, and the distribution of Eddington ratios of BL Lac objects/quasars exhibits a bimodal nature, which imply that the accretion mode of BL Lac objects may be different from that of radio quasars.