The Locus of Highly Accreting Active Galactic Nuclei on theMBH‐σ Plane: Selections, Limitations, and Implications

We re-examine the locus of narrow line Seyfert 1 galaxies on the M_BH--sigma(black hole mass--bulge velocity dispersion) plane in the light of the resultsfrom large new optically selected samples. We find that (1) soft X-ray selectedNLS1s have a lower ratio of BH mass to \sigma^{4}_{[OIII]} than broad lineSeyfert 1 galaxies; this remains a robust statistical result contrary to recentclaims otherwise; (2) optically selected NLS1s have systematically lowerEddington luminosity ratio compared to X-ray selected NLS1s; and (3) as aresult, the locus of NLS1s on the M_BH--sigma plane is affected by selectioneffects. We argue that there is no single explanation for the origin of theM_BH--sigma relation; instead tracks of galaxies on the M_BH--sigma planediffer with redshift, consistent with the downsizing of AGN activity. If theseresults at face value are incorrect, then the data imply that AGNs with highEddington accretion reside preferentially in relatively late type galaxies atthe present epoch, perhaps a more interesting result and a challenge totheoretical models.Comment: To appear in Ap