A Bar Fuels a Supermassive Black Hole?: Host Galaxies of Narrow‐Line Seyfert 1 Galaxies

We present optical images of nearby 50 narrow-line Seyfert 1 galaxies (NLS1s)which cover all the NLS1s at z<0.0666 and $\delta \ge -25^{\circ}$ known at thetime of 2001. Among the 50 NLS1s, 40 images are newly obtained by ourobservations and 10 images are taken from archive data. Motivated by thehypothesis 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 triggermechanism(s) of active galactic nuclei (AGNs) by seeing the early phase of AGN.With these images, we made morphological classification by eye inspection andby quantitative method, and found a high bar frequency of the NLS1s in theoptical band; the bar frequency is $85 \pm 7% among disk galaxies ($64- 71$% intotal sample) which is more frequent than that (40-70%) of broad-line Seyfert 1galaxies (BLS1s) and normal disk galaxies, though the significance is marginal.Our results confirm the claim by Crenshaw et al. (2003) with a similar analysisfor 19 NLS1s. The frequency is comparable to that of HII/starburst galaxies. Wealso examined the bar frequency against width of the broad H$\beta$ emissionline, Eddington ratio, and black hole mass, but no clear trend is seen.Possible implications such as an evolutionary sequence from NLS1s to BLS1 arediscussed briefly.