Detailed Analysis of Balmer Lines in a Sloan Digital Sky Survey Sample of 90 Broad Line Active Galactic Nuclei

TL;DR

This study analyzes the spectral properties of 90 broad line AGN from SDSS, focusing on Balmer lines to understand the physical conditions of the Broad Line Region and its relation to black hole properties.

Contribution

It provides detailed flux and profile measurements of Balmer lines in a large AGN sample and explores their relation to black hole mass and accretion rates using the Boltzmann Plot method.

Findings

Broader AGN have larger H_alpha / H_beta ratios.

Broader AGN have smaller H_gamma / H_beta and H_delta / H_beta ratios.

Balmer line ratios relate to BLR structure and accretion processes.

Abstract

In order to contribute to the general effort aiming at the improvement of our knowledge about the physical conditions within the Broad Line Region (BLR) of Active Galactic Nuclei (AGN), here we present the results achieved by our analysis of the spectral properties of a sample of 90 broad line emitting sources, collected at the Sloan Digital Sky Survey (SDSS) database. By focusing our attention mainly onto the Balmer series of hydrogen emission lines, which is the dominant feature in the optical wavelength range of many BLR spectra, we extracted several flux and profile measurements, which we related to other source properties, such as optical continuum luminosities, inferred black hole masses, and accretion rates. Using the Boltzmann Plot method to investigate the Balmer line flux ratios as a function of the line profiles, we found that broader line emitting AGN typically have larger H_alpha / H_beta and smaller H_gamma / H_beta and H_delta / H_beta line ratios. With the help of some recent investigations, we model the structure of the BLR and we study the influence of the accretion process on the properties of the BLR plasma.