Empirical Links between XRB and AGN accretion using the complete z<0.4 spectroscopic CSC/SDSS Catalog

TL;DR

This study investigates the similarities between X-ray binary systems and active galactic nuclei by analyzing a large sample of sources, revealing correlations between spectral properties and accretion rates, with some differences from XRB analogies.

Contribution

It provides a comprehensive analysis of X-ray and optical spectral characteristics across diverse AGN and galaxy types, updating key relationships and testing analogies with XRB accretion states.

Findings

Confirmed a trend between X-ray spectral hardness and Eddington ratio in AGN.

Found the aox spectral slope correlates with Eddington ratio, but not as predicted by XRB analogy.

Observed significant dispersion in the spectral hardness-Eddington ratio relationship.

Abstract

Striking similarities have been seen between accretion signatures of Galactic X-ray binary (XRB) systems and active galactic nuclei (AGN). XRB spectral states show a V-shaped correlation between X-ray spectral hardness and Eddington ratio as they vary, and some AGN samples reveal a similar trend, implying analogous processes at vastly larger masses and timescales. To further investigate the analogies, we have matched 617 sources from the Chandra Source Catalog to SDSS spectroscopy, and uniformly measured both X-ray and optical spectral characteristics across a broad range of AGN and galaxy types. We provide useful tabulations of X-ray spectral slope for broad and narrow line AGN, star-forming and passive galaxies and composite systems, also updating relationships between optical (Ha and [OIII]) line emission and X-ray luminosity. We further fit broadband spectral energy distributions with a variety of templates to estimate bolometric luminosity. Our results confirm a significant trend in AGN between X-ray spectral hardness and Eddington ratio expressed in X-ray luminosity, albeit with significant dispersion. The trend is not significant when expressed in the full bolometric or template-estimated AGN luminosity. We also confirm a relationship between the X-ray/optical spectral slope aox, and Eddington ratio, but it may not follow the trend predicted by analogy with XRB accretion states.