Contribution of a Disk Component to Single Peaked Broad Lines of Active Galactic Nuclei

TL;DR

This study investigates the hidden disk component in single-peaked broad emission lines of AGN, suggesting that disk emission may be present even without double-peaked profiles, mainly at low inclinations and with a smaller flux contribution.

Contribution

It introduces a two-component BLR model and compares simulated and observed line profiles to reveal hidden disk emission in single-peaked AGN lines.

Findings

Hidden disk emission may be present in single-peaked BELs.

Disk inclination is generally small, less than 25 degrees.

Disk contribution to total flux is smaller than surrounding region.

Abstract

We study the disk emission component hidden in the single-peaked Broad Emission Lines (BELs) of Active Galactic Nuclei (AGN). We compare the observed broad lines from a sample of 90 Seyfert 1 spectra taken from the Sloan Digital Sky Survey with simulated line profiles. We consider a two-component Broad Line Region (BLR) model where an accretion disk and a surrounding non-disk region with isotropic cloud velocities generate the simulated BEL profiles. The analysis is mainly based in measurements of the full widths (at 10%, 20% and 30% of the maximum intensity) and of the asymmetries of the line profiles. Comparing these parameters for the simulated and observed H$\alpha$ broad lines, we {found} that the hidden disk emission {may} be present in BELs even if the characteristic {of two peaked line profiles is} absent. For the available sample of objects (Seyfert 1 galaxies with single-peaked BELs), our study indicates that, {in the case of the hidden disk emission in single peaked broad line profiles}, the disk inclination tends to be small (mostly $i<25^\circ$) and that the contribution of the disk emission to the total flux should be smaller than the contribution of the surrounding region.