Evolution of Active Galaxies: Black-hole Mass - Bulge relations for Narrow Line Objects

Abstract

Mathur (2000) has proposed that the narrow line Seyfert 1 galaxies (NLS1s) are likely to be the active galaxies in early stage of evolution. To test this hypothesis, we have calculated the black hole (BH) masses and the host galaxy bulge masses for a sample of NLS1s. We find that the mean BH to bulge mass ratio of NLS1s is significantly smaller than that for normal Seyfert galaxies. We also find that the ratio of BH mass to bulge velocity dispersion is also significantly smaller for NLS1s. A scenario of BH growth is our preferred interpretation, though alternative explanations are discussed. Assuming that the BHs grow with accretion with a radiative efficiency of 0.1, it will take them about $3.3\times 10^8$ years to become as massive as in normal Seyfert 1s. These timescales are consistent with the theoretical estimates of quasar timescale $t_Q$ less than about $4.5\times 10^8$ years calculated by Haehnelt, Natarajan & Rees (1998). Studies of low redshift NLS1s thus provide a powerful, and due to their proximity relatively easy, way to understand the high redshift quasars and their evolution.