Radiation pressure on dust explaining the low ionized broad emission lines in active galactic nuclei

Abstract

Context. Broad emission lines are the most characteristic features in the spectra of galaxies with an active galactic nucleus (AGN). They mostly show either single-peaked or double-peaked profiles and originate from a complex dynamics of the likely discrete clouds moving in a spatially extended region known as the broad line region (BLR). Aims. In this paper, we present a large grid of results, which is used to test the model based on calculations of the spectral line generic profiles. Methods. We followed a non-hydrodynamical single-cloud approach to BLR dynamics based on a radiatively dust-driven model. We previously showed in detail that the 2.5D version of the model could provide us with the 3D geometry of the BLR. Results. We show that the shape of profiles not only depends on the accretion rate of the source, the black hole mass, and the viewing angle, but it is most significantly affected by the adopted dust-to-gas mass ratio regulating the strength of the radiation pressure. We also show that the model can aptly explain the low ionized broad emission lines of the mean spectrum of quasars, such as MgII and Hβ. Conclusions. The radiatively dust-driving mechanism can appropriately account for the low-ionized part of BLR of AGNs.