Double-Peaked Narrow Emission Lines in AGN: The Role of Rotating Disks

TL;DR

This paper investigates double-peaked narrow emission lines in AGN, proposing that rotating gaseous disks are a likely cause, supported by spectroscopic indicators showing similarities in emission line ratios.

Contribution

It introduces the concept of equal-peaked AGN as likely caused by rotating disks, supported by specific spectroscopic evidence differentiating them from binary AGN or outflows.

Findings

EPAGN have lower [Ne V]/[O III] ratios than non-double peaked AGN.

[O III]/H-beta ratios are more similar in red and blue components of EPAGN.

Spectroscopic evidence favors rotating disks over binary AGN as the cause.

Abstract

AGN with double-peaked narrow lines (DPAGN) may be caused by kiloparsec scale binary AGN, bipolar outflows, or rotating gaseous disks. We examine the class of DPAGN in which the two narrow line components have closely similar intensity as being especially likely to involve disks or jets. Two spectroscopic indicators support this likelihood. For DPAGN from Smith et al. (2010), the "equal-peaked" objects (EPAGN) have [Ne V]/[O III] ratios lower than for a control sample of non-double peaked AGN. This is unexpected for a pair of normal AGN in a galactic merger, but may be consistent with [O III] emission from a rotating ring with relatively little gas at small radii. Also, [O III]/H-beta ratios of the redshifted and blueshifted systems in the EPAGN are more similar to each other than in a control sample, suggestive of a single ionizing source and inconsistent with the binary interpretation.