Association of Optical, Ultraviolet and Soft X-ray excess Emissions in AGNs

TL;DR

This study investigates the relationships between optical, UV, and soft X-ray emissions in AGNs, revealing correlations and dependencies that shed light on the structure and emission regions within active galactic nuclei.

Contribution

It provides new empirical relations linking soft X-ray, optical, and UV emissions with spectral line properties, enhancing understanding of emission region geometries in AGNs.

Findings

FWHM of MgII correlates with Hβ, indicating different emission regions.

Strong correlation between optical and UV luminosities.

Optical continuum's dependence on soft X-ray excess varies with redshift.

Abstract

Soft X-ray emission (0.5--2.0 keV) plays a pivotal role in regulating the optical and UV emission in the AGNs. We collected a sample of 1811 AGNs from the SDSS database and obtained various parameters of Balmer lines, optical continuum, MgII line \& UV continuum and studied their dependencies on soft X-ray luminosity. Based on the linear regression analysis, we found that FWHM$_{\text{MgII}}$ $\propto$ FWHM$_{\text{H}\beta}^{0.554}$ suggesting that UV emission is arising from a region relatively outside the broad line region (BLR) associated to the H$\beta$ emission and found a strong correlation between optical and UV luminosities (L$_{\text{MgII}}$ $\propto$ L$_{\text{H}\beta}^{0.822}$). It was noticed that the dependency of optical continuum luminosities on soft excess changes with the redshift (L$_{\text{X}}$ $\propto$ L$^{0.596}_{5100\text{\AA}}$ for z < 0.5 and L$_{\text{X}}$ $\propto$ L$^{0.429}_{5100\text{\AA}}$ for z > 0.5). The FWHM components of H${\beta}$ and MgII core components were found to be virialized and is not affected by the soft excess emission whereas the wings of MgII display a dependency. We estimated a relation viz. L$_{\text{X}}$ $\propto$L$^{0.520}_{3000\text{\AA}}$ FWHM$^{0.525}_{\text{MgII}}$ and found to be well in agreement with a proposed physical scenario. All the derived relations were used to understand the inter-modulating association of the BLR and disc in the AGNs.