A spectroscopic analysis of a sample of narrow-line Seyfert 1 galaxies selected from the Sloan Digital Sky Survey

TL;DR

This study provides a detailed spectroscopic analysis of 296 narrow-line Seyfert 1 galaxies from SDSS, revealing their properties, similarities with broad-line Seyfert 1s, and evidence of high-velocity outflows linked to luminosity and accretion rates.

Contribution

It offers a homogeneous spectroscopic characterization of NLS1s, clarifies their relation to BLS1s, and investigates emission line kinematics and outflow mechanisms.

Findings

NLS1s predominantly have Lorentzian Balmer lines and high Eddington ratios.

Fe II emission is not unique to NLS1s, with similar low values observed.

Most NLS1s exhibit high-velocity outflows in the narrow-line region.

Abstract

We revisited the spectroscopic characteristics of narrow-line Seyfert 1 galaxies (NLS1s) by analysing a homogeneous sample of 296 NLS1s at redshift between 0.028 and 0.345, extracted from the Sloan Digital Sky Survey (SDSS-DR7) public archive. We confirm that NLS1s are mostly characterized by Balmer lines with Lorentzian profiles, lower black hole masses and higher Eddington ratios than classic broad-line Seyfert 1 (BLS1s), but they also appear to be active galactic nuclei (AGNs) contiguous with BLS1s and sharing with them common properties. Strong Fe II emission does not seem to be a distinctive property of NLS1s, as low values of Fe II/H$\beta$ are equally observed in these AGNs. Our data indicate that Fe II and Ca II kinematics are consistent with the one of H$\beta$. On the contrary, O I $\lambda$8446 seems to be systematically narrower and it is likely emitted by gas of the broad-line region more distant from the ionizing source and showing different physical properties. Finally, almost all NLS1s of our sample show radial motions of the narrow-line region highly-ionised gas. The mechanism responsible for this effect is not yet clear, but there are hints that very fast outflows require high continuum luminosities (> $10^{44}$ erg/s) or high Eddington ratios (log(L$_{\rm bol}$/L$_{\rm Edd}$) > -0.1).