partly obscured accretion disk model to explain Shifted broad Balmer emission lines of Active Galactic Nuclei

TL;DR

This paper proposes a partly obscured accretion disk model to explain shifted broad Balmer emission lines in AGN, challenging the traditional interpretation of radial gas motion and providing better estimates of black hole masses.

Contribution

The study introduces a novel partly obscured disk-like BLR model that accounts for shifted broad emission lines and reconciles discrepancies in black hole mass estimates.

Findings

Partly obscured disk models can produce shifted broad lines.

Virial BH masses are systematically lower than M-sigma estimates.

The model explains underestimated virial BH masses in AGN with shifted lines.

Abstract

We present a new model to explain the appearance of red/blue-shifted broad low-ionization emission lines, especially emission lines in optical band, which is commonly considered as an indicator of radial motion of the line emitting gas in broad emission line regions (BLRs) of Active Galactic Nuclei (AGN). We show that partly obscured disk-like BLRs of dbp emitters (AGN with double-peak broad low-ionization emission lines) can also successfully produce shifted standard Gaussian broad balmer emission lines. Then we calculate two kinds of BH masses for AGN with shifted broad balmer emission lines selected from SDSS. We find that the BH masses calculated from M-sigma relation are systematically larger than virial BH masses for the selected objects, even after the correction of internal reddening effects in BLRs. The smaller virial BH masses than BH masses from M-sigma relation for objects with shifted broad emission lines are coincident with what we expect from the partly obscured accretion disk model. Thus, we provide an optional better model to explain the appearance of shifted broad emission lines, especially for those objects with underestimated virial BH masses.