Optical emission line properties of Narrow Line Seyfert 1s and comparison AGN

TL;DR

This study uses spectroscopic data to analyze emission line properties in Narrow Line Seyfert 1 galaxies, revealing complex kinematic components and potential diagnostics for physical conditions near the active nucleus.

Contribution

It provides detailed modeling of emission line profiles in NLS1s and compares these with other AGN types, highlighting unique kinematic features and potential diagnostic line ratios.

Findings

NLS1s require an additional broad emission component (~3000 km/s).

Forbidden high ionisation lines trace an intermediate velocity region.

Variability in [Fe X] and [Fe XI] line ratios suggests diagnostic potential.

Abstract

Based on a new spectroscopic sample observed using the WHT, we examine the kinematic properties of the various emission line regions in narrow line Seyfert 1 galaxies (NLS1s) by modelling their profiles using multiple component fits. We interpret these results by comparison with velocity components observed for different lines species covered in the same spectrum, and equivalent components measured in the spectra of some broad line Seyfert 1s and a representative Seyfert 2 galaxy. We find that the fits to the Halpha and Hbeta line profiles in NLS1s require an additional broad (~3000km/s) component that might correspond to a suppressed broad line region with similar kinematics to those of typical broad line Seyfert 1s. From the profiles of the forbidden high ionisation lines (FHILs) in NLS1s, we find evidence that they appear to trace an `intermediate' velocity region with kinematics between the standard broad and narrow line regions. Weaker evidence of this region is also present in the profiles of the permitted Balmer lines. Finally, we note that despite having similar ionisation potentials, the relative intensities of the highly ionised lines of [Fe X]6374 and [FeXI]7892 show considerable dispersion from one galaxy to another. The interpretation of this requires further modelling, but suggests the possibility of using the ratio as a diagnostic to constrain the physical conditions of the FHIL emitting region and possibly the shape of the spectral energy distribution in the vicinity of 200eV. This spectral region is very difficult to observe directly due to photoelectric absorption both in our Galaxy and intrinsic to the source.