The black hole--bulge relation in AGNs

Abstract

We used the widths of H$β$ and [OIII] emission lines to investigate the black hole--bulge relation in radio-loud AGNs, radio-quiet AGNs and NLS1s. The central black hole mass, $M_{bh}$, is estimated from the H$β$ line width and the optical luminosity, and the bulge velocity dispersion, $σ$, is directly from the width of [OIII] line. We found that the radio-quiet AGNs follow the established $M_{bh}-σ$ relationship in nearby inactive galaxies, while the radio-loud AGNs and NLS1s deviate from this relationship. There are two plausible interpretations for the deviation of radio-loud AGNs. One is that the size of broad line regions (BLRs) emitting H$β$ line is overestimated because of the overestimation of optical luminosity, the other is that the dynamics of BLRs and/or narrow line regions (NLRs) in radio-loud AGNs is different from that in radio-quiet AGNs. The deviation of NLS1s may be due to the small inclination of BLRs to the line of sight or the reliability of [OIII] line width as the indicator of stellar velocity dispersion because of its complex multiple components.