Scattered X-rays in Obscured Active Galactic Nuclei and their Implications for Geometrical Structure and Evolution

TL;DR

This study analyzes 32 obscured AGNs to understand how their scattering fractions relate to their geometrical structure and evolution, revealing that smaller scattering fractions indicate thicker tori and potential links to black hole growth.

Contribution

It introduces a new sample of obscured AGNs and explores the relationship between scattering fraction, geometry, and black hole properties, highlighting the role of torus structure.

Findings

Low scattering fraction AGNs have smaller narrow-line regions.

No significant correlation between scattering fraction and far-infrared luminosity.

Weak anti-correlation between Eddington ratio and scattering fraction.

Abstract

We construct a new sample of 32 obscured active galactic nuclei (AGNs) selected from the Second XMM-Newton Serendipitous Source Catalogue to investigate their multiwavelength properties in relation to the "scattering fraction", the ratio of the soft X-ray flux to the absorption-corrected direct emission. The sample covers a broad range of the scattering fraction (0.1%-10%). A quarter of the 32 AGNs have a very low scattering fraction (smaller than 0.5%), which suggests that they are buried in a geometrically thick torus with a very small opening angle. We investigate correlations between the scattering fraction and multiwavelength properties. We find that AGNs with a small scattering fraction tend to have low [O III]lambda5007/X-ray luminosity ratios. This result agrees with the expectation that the extent of the narrow-line region is small because of the small opening angle of the torus. There is no significant correlation between scattering fraction and far-infrared luminosity. This implies that a scale height of the torus is not primarily determined by starburst activity. We also compare scattering fraction with black hole mass or Eddington ratio and find a weak anti-correlation between the Eddington ratio and scattering fraction. This implies that more rapidly growing supermassive black holes tend to have thicker tori.