Seyfert 2 galaxies with unusually wide nebular lines

TL;DR

This paper identifies and analyzes a subset of Seyfert 2 galaxies with unusually broad narrow emission lines, revealing complex gas dynamics and proposing explanations for these spectral peculiarities.

Contribution

It reports the discovery of 14 Seyfert 2 galaxies with unusually wide nebular lines and characterizes their complex velocity structures, a novel subclass within Seyfert 2s.

Findings

14 objects with broad, overlapping nebular lines identified

Spectral analysis reveals multiple velocity components in narrow lines

Possible new subclass of Seyfert 2 galaxies with complex gas kinematics

Abstract

We report on a set of AGN that match the Seyfert 2 galaxy classification criteria, but display unusually wide "narrow" lines, with the 4959 {\AA} and 5007 {\AA} nebular lines overlapping with each other. This spectral line broadening is in most cases evidence of a complex profile with multiple components. It indicates an unusual narrow line region with diverse gas clouds and a range of velocity systems. We list 14 such objects with these characteristics identified in a set of Sloan Digital Sky Survey spectra. We measure the strengths of all lines visible in the spectrum, and attempt to fit multiple Gaussian profiles to the nebular lines. We quantify the line parameters of all multiple velocity systems discovered. We compare the spectral characteristics of our sample with those of other, 'conventional' type 2 Seyferts and attempt to determine whether other systematic spectral differences exist. We consider whether the investigated sample constitutes a clear sub-class of the Seyfert 2 population. In conclusion we offer possible explanations for the unusual line profiles.