Detection of faint broad emission lines in type 2 AGN: I. Near infrared observations and spectral fitting

TL;DR

This study uses near-infrared spectroscopy to detect faint broad emission lines in obscured type 2 AGN, revealing broad line region components in a subset of these objects and comparing their properties with type 1 AGN.

Contribution

First systematic near-infrared spectral analysis of a sample of obscured AGN revealing broad line regions, expanding understanding of AGN unification models.

Findings

Broad line region components detected in 13 of 41 AGN2.

Detected broad lines have smaller FWHM compared to type 1 AGN.

Detection does not depend on spectral quality or orientation effects.

Abstract

We present medium resolution near infrared spectroscopic observations of 41 obscured and intermediate class AGN (type 2, 1.9 and 1.8; AGN2) with redshift $z \lesssim$0.1, selected from the Swift/BAT 70-month catalogue. The observations have been carried out in the framework of a systematic study of the AGN2 near infrared spectral properties and have been executed using ISAAC/VLT, X-shooter/VLT and LUCI/LBT, reaching an average S/N ratio of $\sim$30 per resolution element. For those objects observed with X-shooter we also obtained simultaneous optical and UV spectroscopy. We have identified a component from the broad line region in 13 out of 41 AGN2, with FWHM ${\rm > 800 }$ km/s. We have verified that the detection of the broad line region components does not significantly depend on selection effects due to the quality of the spectra, the X-ray or near infrared fluxes, the orientation angle of the host galaxy or the hydrogen column density measured in the X-ray band. The average broad line region components found in AGN2 has a significantly (a factor 2) smaller FWHM if compared with a control sample of type 1 AGN.