Seyfert Galaxies in the Local Universe: Analysis of Spitzer Spectra of a Complete Sample

TL;DR

This study analyzes Spitzer spectra of 72 Seyfert galaxies to quantify starburst activity and AGN dominance, revealing differences in properties between Seyfert 2s with and without hidden broad line regions.

Contribution

It provides a comprehensive mid-IR spectral analysis of a complete Seyfert galaxy sample, introducing diagnostic tools to distinguish starburst and AGN contributions.

Findings

Starburst components quantified by PAH and H2 features.

AGN dominance measured by fine structure line ratios.

Seyfert 2s with hidden broad lines show higher AGN dominance.

Abstract

The Spitzer high resolution spectra of 72 Seyfert galaxies from the 12$\mu$m Galaxy Sample are presented and discussed. The presence of starburst components in these galaxies can be quantified by powerful mid-IR diagnostics tools (i.e. 11.25$\mu$m PAH feature equivalent width and the H$_2$ emission line intensity), as well as the AGN dominance can be measured by specific fine structure line ratios (e.g. [NeV]/[NeII], [NeV]/[SiII], etc.). The two types of Seyfert galaxies do not show any statistical difference in our diagnostic tools. However, the Seyfert 2's showing hidden Broad Line Regions in spectro-polarimetric observations have on average an higher AGN dominance, a weaker star formation component and a warmer [60 - 25] spectral index than those without broad emission lines.