A search for non-hidden broad-line region Seyfert 2 galaxies

TL;DR

This study investigates Seyfert 2 galaxies to identify those without hidden broad-line regions, challenging the unified model, and finds a significant subset likely lacking BLRs based on Eddington ratios.

Contribution

It provides evidence for non-HBLR Seyfert 2 galaxies and supports the theory linking BLR presence to Eddington ratios, offering new insights into AGN structure.

Findings

26 non-HBLR Seyfert 2 candidates identified

5 objects may be LINERs

Supports the Eddington ratio threshold for BLR formation

Abstract

According to the unified model of active galactic nuclei, Seyfert 2 galaxies are physically the same as Seyfert 1 objects and they possess a broad-line region (BLR), but it is hidden from the observer due to their orientation. In the past few years, various authors reported that not all Seyfert 2 galaxies harbor a BLR. We compiled a sample of 38 Seyfert 2 galaxies to find non-hidden broad-line region (non-HBLR) objects. Using the theory of Nicastro et al. which suggests the existence of a critical value of the Eddington ratio below which BLR can't be formed, we found 26 non-HBLR Seyfert 2 candidates. We found also that 5 of these 26 non-HBLR objects could be low-ionization nuclear emission-line regions (LINERs).