Evolution of active galaxies: black-hole mass-bulge relations for narrow line objects

Mathur [MNRAS Letters 314 (2000) L17] has proposed that the narrow line Sey fert 1 galaxies (NLS1s) are likely to be the active galaxies in the early s tage of evolution. To test this hypothesis, we have calculated the black ho le (BH) masses and the host galaxy bulge masses for a sample of NLS1s. We f ind 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 ma ss to bulge velocity dispersion is also significantly smaller for NLS1s. A scenario of BH growth is our preferred interpretation, though alternative e xplanations are discussed. Assuming that the BHs grow with accretion with a radiative efficiency of 0.1, it will take them t greater than or similar t o 3.3 x 10(8) years to become as massive as in normal Seyfert 1s. These tim escales are consistent with the theoretical estimates of quasar timescale t (Q) less than or similar to 4.5 x 10(8) years calculated by Haehnelt et al. [MNRAS 300 (1998) 817]. Studies of low redshift NLS1s thus provide a power ful, and due to their proximity, relatively easy way to understand the high redshift quasars and their evolution. (C) 2001 Elsevier Science B. V. All rights reserved.