Evidence for Obscured broad \oiii Components in Type-2 AGN

TL;DR

This study finds evidence of obscured broad \\oiii components in Type-2 AGN, supporting the idea that central outflows and emission regions are affected by dust obscuration, and refines the understanding of AGN unification models.

Contribution

It provides observational evidence for obscured broad \\oiii components in Type-2 AGN, highlighting their role in central outflows and emission line diagnostics, which was not clearly established before.

Findings

Lower flux ratios of broad to core \\oiii in Type-2 AGN.

Broad \\oiii components originate near the central black hole.

Obscured broad \\oiii explains flux ratio differences in BPT diagram.

Abstract

In the manuscript, we report evidence on broad \oiii components apparently obscured in Type-2 AGN under the framework of the Unified model, after checking properties of broad \oiii emissions in large samples of Type-1 and Type-2 AGN in SDSS DR12. We can well confirm the statistically lower flux ratios of the broad to the core \oiii components in Type-2 AGN than in Type-1 AGN, which can be naturally explained by stronger obscured broad \oiii components by central dust torus in Type-2 AGN, unless the Unified model for AGN was not appropriate to the narrow emission lines. The results provide further evidence to support broad \oiii components coming from emission regions nearer to central BHs, and also indicate the core \oiii component as the better indicator for central activities in Type-2 AGN, due to few effects of obscuration on the core \oiii component. Considering the broad \oiii components as signs of central outflows, the results provide evidence for strong central outflows being preferentially obscured in Type-2 AGN. Furthermore, the obscured broad \oiii component can be applied to explain the different flux ratios of \oiiihb between Type-1 and Type-2 AGN in the BPT diagram.