Hidden Double-Peaked Emitters in Seyfert 2 Galaxies

TL;DR

This paper reports the discovery of variable, double-peaked, polarized broad Halpha emission lines in Seyfert 2 galaxies, revealing hidden broad-line regions and scattering regions close to the nucleus.

Contribution

It provides evidence for compact scattering clouds near the nucleus, likely part of the clumpy torus, explaining hidden broad-line regions in Seyfert 2 galaxies.

Findings

Detection of variable, double-peaked, polarized broad Halpha lines in NGC 2110 and NGC 5252.

Scattering clouds are compact, within ~10 pc, and possibly part of the torus.

These galaxies are the hidden counterparts to broad-line double-peaked AGNs.

Abstract

We present the detection of extremely broad, double-peaked, highly polarized Halpha emission lines in the nuclei of the well-known Seyfert 2 galaxies NGC 2110 and NGC 5252. These hidden broad Halpha emission lines, visible only in scattered light, are shown to display significant variability in strength and profile on timescales of <~ 1 yr. That the broad emission line exhibits variability in polarized flux also suggests that the scattering region must be very compact, possibly confined in a small number of electron clouds <~ 1 lt-yr in size. Our observational constraints place these clouds within ~10 pc of the nucleus with temperatures < 10^6 K and densities ~ 10^7 cm^-3, consistent with a region just outside the obscuring torus between the broad-line region and narrow-line region. These scattering clouds could arise from the clumpy torus itself. These findings and other properties indicate that NGC 2110 and NGC 5252 are the hidden counterparts to the broad-line double-peaked emission-line AGNs, whose examples include Arp 102B and 3C 332.