The Locus of Highly Accreting Active Galactic Nuclei on the M_BH-σ Plane: Selections, Limitations, and Implications

We reexamine the locus of narrow-line Seyfert 1 galaxies (NLS1s) on the M_BH-σ (black hole mass-bulge velocity dispersion) plane in the light of the results from large new optically selected samples. We find that (1) soft X-ray-selected NLS1s have a lower ratio of BH mass to σ than broad-line Seyfert 1 galaxies; this remains a robust statistical result, contrary to recent claims otherwise; (2) optically selected NLS1s have systematically lower Eddington luminosity ratios than X-ray-selected NLS1s; and (3) as a result, the locus of NLS1s on the M_BH-σ plane is affected by selection effects. We argue that there is no single explanation for the origin of the M_BH-σ relation; instead tracks of galaxies on the M_BH-σ plane differ with redshift, consistent with the downsizing of AGN activity. If these results at face value are incorrect, then the data imply that AGNs with high Eddington accretion reside preferentially in relatively late type galaxies at the present epoch, perhaps a more interesting result and a challenge to theoretical models.