First observation of double-peaked O I emission in the near-infrared spectrum of an active galaxy

TL;DR

This paper reports the first detection of double-peaked O I emission in the near-infrared spectrum of an active galaxy, revealing disk-like broad-line region geometry through spectral analysis.

Contribution

It presents the first unambiguous detection of multiple broad double-peaked NIR emission lines in an active galaxy and models their profiles to infer BLR geometry.

Findings

Detection of double-peaked O I λ11297 emission line.

Simultaneous detection of double-peaked Paα and likely He II λ10830 lines.

BLR in III Zw 002 has a disk-like structure extending to its outer edge.

Abstract

Double-peaked profiles associated with the broad-line region (BLR) of active galactic nuclei (AGNs) are regarded as the clearest evidence of the presence of an accretion disk. They are most commonly detected by means of optical spectroscopy in the Balmer lines and in the Mg II $\lambda$2798 ultraviolet line. Here, we report the first unambiguous detection of a double-peak broad emission line associated with the O I $\lambda$11297 emission line in the near-infrared (NIR) in the local Seyfert 1 galaxy III Zw 002. Additionally, we detect simultaneously in the spectrum the double-peak emission in the Pa$\alpha$ line and very likely in the He II $\lambda$10830. This is the first time that several broad double-peaked NIR emission lines have been detected simultaneously. The double-peaked profiles are fit using a disk-based model, with an additional Gaussian component attributed to nondisk clouds, which represents the classical BLR. Our results obtained from the fits reveal important parameters, such as disk inclination and geometry. From the double-peaked profile fits, we suggest that the BLR in III Zw 002 has a disk-like geometry, as it extends up to the outer edge of the BLR.