A Bar Fuels a Super-Massive Black Hole?: Host Galaxies of Narrow-Line Seyfert 1 Galaxies

Abstract

We present optical images of nearby 50 narrow-line Seyfert 1 galaxies (NLS1s) which cover all the NLS1s at z<0.0666 and $δ\ge -25^{\circ}$ known at the time of 2001. Among the 50 NLS1s, 40 images are newly obtained by our observations and 10 images are taken from archive data. Motivated by the hypothesis that NLS1s are in an early phase of a super-massive black hole (BH) evolution, we present a study of NLS1 host galaxy morphology to examine trigger mechanism(s) of active galactic nuclei (AGNs) by seeing the early phase of AGN. With these images, we made morphological classification by eye inspection and by quantitative method, and found a high bar frequency of the NLS1s in the optical band; the bar frequency is $85 \pm 7% among disk galaxies ($64- 71$% in total sample) which is more frequent than that (40-70%) of broad-line Seyfert 1 galaxies (BLS1s) and normal disk galaxies, though the significance is marginal. Our results confirm the claim by Crenshaw et al. (2003) with a similar analysis for 19 NLS1s. The frequency is comparable to that of HII/starburst galaxies. We also examined the bar frequency against width of the broad H$β$ emission line, Eddington ratio, and black hole mass, but no clear trend is seen. Possible implications such as an evolutionary sequence from NLS1s to BLS1 are discussed briefly.