Black Hole – Bulge Relation for Narrow-Line Objects

It has been thought that narrow-line Seyfert 1 galaxies are likely to be in the early stages of the evolution of active galaxies. To test this suggestion, the ratios of the central massive black hole (MBH) mass to the bulge mass (Mbh/Mbulge) were estimated for 22 Narrow Line AGNs (NL AGNs). It is found that NL AGNs appear to have genuinely lower MBH/Bulge mass ratio (Mbh/Mbulge). The mean log(Mbh/Mbulge) for 22 NL AGNs is −3.9± 0.07, which is an order of magnitude lower than that for Broad Line AGNs and quiescent galaxies. We suggest a nonlinear MBH/Bulge relation and find there exists a relation between the Mbh/Mbulge and the velocity dispersion, σ, derived from the [O III] width. A scenario of MBH growth for NL AGNs is one of our interpretations of the nonlinear MBH/Bulge relation. The MBH growth timescales for 22 NL AGNs were calculated, with a mean value (1.29± 0.24)× 10 yr. Another plausible interpretation is also possible: that NL AGNs occur in low-Mbulge galaxies and that in such galaxies Mbh/Mbulge is lower than that in galaxies with a higher Mbulge, if we consider that NL AGNs already have their “final” Mbh/Mbulge. More information of the bulge in NL AGNs is needed to clarify the black hole – bulge relation.