Probing Accretion Disk Winds in AGN - Asymmetric broad Balmer Emission Lines

TL;DR

This study investigates the asymmetry of broad Balmer emission lines in AGN spectra to understand accretion disk winds, revealing correlations with line width, luminosity, radio flux, and ionization degree using SDSS data.

Contribution

It introduces a detailed analysis of line asymmetry and kurtosis in AGN spectra, linking these features to accretion disk wind properties for the first time.

Findings

Asymmetry correlates with line width and luminosity.

Kurtosis varies systematically with emission line properties.

Asymmetry index depends on radio flux and ionization degree.

Abstract

The Broad Line Region of Active Galactic Nuclei is characterized by broad Balmer emission lines in their optical spectra. The broad Balmer emission lines are found to be asymmetric, some blue sided and others red sided in their asymmetry. One of the components behind the asymmetry is thought to be an accretion disk wind. We probe the accretion disk wind using the broad balmer emission line profiles. This asymmetry of the broad balma emission line profiles is measured in velocity space after a measurement of the line shift at percentiles from 0, in increaments of 10, up to 90. In addition, the Kurtosis Index is obtained at appropriate points of the emission lines' profiles. This study is based on many hundreds of SDSS spectra, starting with low redshift high signal to noise ratio spectra. We also consider a definite number in each bin of their FWHM, in bins of 1000 km/s (atleast 40 per bin), starting from 1000km/s to the very broad emission lines. We present how strong the asymmetry (by plotting Asymmetry Index as a function of percentile) of the broad/narrow lines (in percent) is, what the Kurtosis $(R20, 80)$ is. We also present what the Asymmetry Index as a function of line width (FWHM), luminosity (V-band), core-radio flux and Ionization Degree. Key Words: AGN: Accretion Disk, Accretion Disk Wind - Line: Asymmetry, Balmer, Emission, Profiles