Narrow double-peaked emission lines of SDSS J131642.90+175332.5: signature of a single or a binary AGN in a merger, jet-cloud interaction, or unusual narrow-line region geometry

摘要

We present an analysis of the active galaxy SDSS J131642.90+175332.5, whichis remarkable because all of its narrow emission lines are double-peaked, andbecause it additionally shows an extra broad component (FHWM ~ 1400 km/s) inmost of its forbidden lines, peaking in between the two narrow systems. Thepeaks of the two narrow systems are separated by 400--500 km/s in velocityspace. The spectral characteristics of double-peaked [O III] emission havepreviously been interpreted as a signature of dual or binary active galacticnuclei (AGNs), among other models. In the context of the binary scenario, SDSSJ131642.90+175332.5 is a particularly good candidate because not just one linebut all of its emission lines are double-peaked. However, we also discuss anumber of other scenarios which can potentially account for double-peakednarrow emission lines, including projection effects, a two-sided outflow,jet-cloud interactions, special narrow-line region (NLR) geometries (disks,bars, or inner spirals), and a galaxy merger with only one AGN illuminating twoNLRs. We argue that the similarity of the emission-line ratios in both systems,and the presence of the very unusual broad component at intermediate velocity,makes a close pair of unrelated AGNs unlikely, and rather argues for processesin a single galaxy or merger. We describe future observations which candistinguish between these remaining possibilities.