Narrow-line Seyfert 1 Galaxies and the M_BH - sigma Relation

TL;DR

This study examines the placement of narrow-line Seyfert 1 galaxies on the M_BH - sigma relation, finding they follow the relation when using specific emission lines as surrogates for stellar velocity dispersion, with implications for galaxy evolution models.

Contribution

It demonstrates that NLS1 galaxies follow the M_BH - sigma relation when using [SII] and corrected [OIII] line widths, clarifying previous discrepancies and refining methods for measuring sigma_*.

Findings

NLS1 galaxies follow the M_BH - sigma relation with [SII] as a surrogate.

Corrected [OIII] line widths align NLS1s with the relation.

Outliers in [OIII] are consistent with the relation when considering [SII].

Abstract

We have studied the location of narrow-line Seyfert 1 (NLS1) galaxies and broad-line Seyfert 1 (BLS1) galaxies on the M_BH - sigma relation of non-active galaxies. We find that NLS1 galaxies as a class - as well as the BLS1 galaxies of our comparison sample - do follow the M_BH-sigma relation of non-active galaxies if we use the width of the [SII]6716,6731 emission lines as surrogate for stellar velocity dispersion, sigma_*. We also find that the width of [OIII]5007 is a good surrogate for sigma_*, but only after (a) removal of asymmetric blue wings, and, more important, after (b) excluding core [OIII] lines with strong blueshifts (i.e., excluding galaxies which have their [OIII] velocity fields dominated by radial motions, presumably outflows). The same galaxies which are extreme outliers in [OIII] still follow the M_BH - sigma relation in [SII]. We confirm previous findings that NLS1 galaxies are systematically off-set from the M_BH - sigma relation if the full [OIII] profile is used to measure sigma. We systematically investigate the influence of several parameters on the NSL1 galaxies' location on the M_BH - sigma plane: [OIII]_core blueshift, L/L_Edd, intensity ratio FeII/H_beta, NLR density, and absolute magnitude. Implications for NLS1 models and for their evolution along the M_BH - sigma relation are discussed.