# BAT AGN Spectroscopic Survey - IV: Near-Infrared Coronal Lines, Hidden Broad Lines, and Correlation with Hard X-ray Emission

## TL;DR

This study provides a detailed NIR spectroscopic analysis of 102 nearby AGN, revealing limitations of line diagnostics for AGN identification, differences in coronal line emission between Seyfert types, and uncovering hidden broad lines in some Seyfert 2s.

## Contribution

It offers the first comprehensive NIR spectroscopic census of a hard X-ray selected AGN sample, highlighting diagnostic limitations and the connection between X-ray and coronal line emission.

## Key findings

- NIR emission line diagnostics are ineffective at identifying bright, nearby AGN.
- Coronal line emission is weaker in Seyfert 2s than in Seyfert 1s of similar luminosity.
- Some Seyfert 2s show broad lines in NIR, indicating less obscuration and host galaxy effects.

## Abstract

We provide a comprehensive census of the near-Infrared (NIR, 0.8-2.4 $\mu$m) spectroscopic properties of 102 nearby (z < 0.075) active galactic nuclei (AGN), selected in the hard X-ray band (14-195 keV) from the Swift-Burst Alert Telescope (BAT) survey. With the launch of the James Webb Space Telescope this regime is of increasing importance for dusty and obscured AGN surveys. We measure black hole masses in 68% (69/102) of the sample using broad emission lines (34/102) and/or the velocity dispersion of the Ca II triplet or the CO band-heads (46/102). We find that emission line diagnostics in the NIR are ineffective at identifying bright, nearby AGN galaxies because ([Fe II] 1.257$\mu$m/Pa$\beta$ and H$_2$ 2.12$\mu$m/Br$\gamma$) identify only 25% (25/102) as AGN with significant overlap with star forming galaxies and only 20% of Seyfert 2 have detected coronal lines (6/30). We measure the coronal line emission in Seyfert 2 to be weaker than in Seyfert 1 of the same bolometric luminosity suggesting obscuration by the nuclear torus. We find that the correlation between the hard X-ray and the [Si VI] coronal line luminosity is significantly better than with the [O III] luminosity. Finally, we find 3/29 galaxies (10%) that are optically classified as Seyfert 2 show broad emission lines in the NIR. These AGN have the lowest levels of obscuration among the Seyfert 2s in our sample ($\log N_{\rm H} < 22.43$ cm$^{-2}$), and all show signs of galaxy-scale interactions or mergers suggesting that the optical broad emission lines are obscured by host galaxy dust.