Are Seyfert 2 Galaxies without Polarized Broad Emission Lines More Obscured?

TL;DR

This study uses XMM-Newton data to compare the obscuration levels in Seyfert 2 galaxies with and without polarized broad lines, finding that those without PBLs are generally more obscured, supporting unification model predictions.

Contribution

It provides new X-ray spectral evidence that Seyfert 2 galaxies without PBLs are more heavily obscured, strengthening the link between obscuration and the absence of polarized broad lines.

Findings

Seyfert 2 galaxies without PBLs tend to have higher obscuration levels.

The difference in absorption indicators between the two groups is statistically significant.

Results support the unification model's explanation of PBL absence due to viewing angle.

Abstract

The new $XMM-Newton$ data of seven Seyfert 2 galaxies with optical spectropolarimetric observations are presented. The analysis of 0.5 -- 10 keV spectra shows that all four Seyfert 2 galaxies with polarized broad lines (PBLs) are absorbed with $N_{\rm H}<10^{24}$ cm$^{-2}$, while two of three Seyfert 2 galaxies without PBLs have evidence suggesting Compton-thick obscuration, supporting the conclusion that Seyfert 2 galaxies without PBLs are more obscured than those with PBLs. Adding the measured obscuration indicators ($N_{\rm H}$, $T$ ratio, and Fe K$\alpha$ line EW) of six luminous AGNs to our previous sample improves the significance level of the difference in absorption from 92.3% to 96.3% for $N_{\rm H}$, 99.1% to 99.4% for $T$ ratio, and 95.3% to 97.4% for Fe K$\alpha$ line EW. The present results support and enhance the suggestions that the absence of PBLs in Seyfert 2 galaxies can be explained by larger viewing angle of line of sight to the putative dusty torus, which lead to the obscuration of broad-line scattering screen, as expected by the unification model.