A Suzaku sample of unabsorbed narrow-line and broad-line Seyfert 1 galaxies: II. Iron emission and absorption

TL;DR

This study analyzes Suzaku observations of Seyfert 1 galaxies, revealing differences in iron emission and absorption features between narrow-line and broad-line types, suggesting variations in their torus geometry and emission regions.

Contribution

It provides a comparative analysis of Fe K band properties in NLS1 and BLS1 galaxies using multiple spectral models, highlighting intrinsic differences.

Findings

Weaker neutral Fe Ka lines in NLS1s compared to BLS1s.

More significant broad emission components in NLS1s.

Similar absorption edge optical depths across both samples.

Abstract

A sample of 22 narrow-line Seyfert 1 (NLS1) and 47 broad-line Seyfert 1 (BLS1) galaxies observed with Suzaku is used to examine the Fe K band properties of each group. Three different models are used to examine the presence of: narrow neutral Fe Ka line at 6.4 keV and ionised Fe xxv and Fe xxvi emission lines (model A); a broad emission feature at around 6 - 7 keV (model B); and an absorption edge at 7.1 keV (model C). In all three models, the neutral Fe Ka line is weaker (lower luminosity and equivalent width) in NLS1s than in BLS1s. Model (B) also finds a more significant broad component (larger equivalent width) in NLS1s than in BLS1s. The feature does not appear to be an artefact of steeper spectra in NLS1s, but rather an intrinsic property of these sources. From model (C), the optical depth of the absorption edge appears comparable between the two samples. When comparing the absorption with the emission line properties, NLS1s seem to exhibit a lower ratio of emission-to-absorption of iron than BLS1s, and than expected based on the fluorescence yield. The observed differences may arise from different torus geometries (e.g. larger opening angle in NLS1s), and/or additional sources of Fe K emission and absorption in NLS1s beyond pure fluorescence (e.g. originating in the disc and broad line region).