Analyzing temporal variations of AGN emission line profiles in the context of (dusty) cloud structure formation in the broad line region

Abstract

The formation processes and the exact appearance of the dust torus and broad line region (BLR) of active galactic nuclei (AGN) are under debate. Theoretical studies show a possible connection between the dust torus and BLR through a common origin in the accretion disk. However observationally the dust torus and BLR are typically studied separately. NGC 4151 is possibly one of the best suited Seyfert 1 galaxies for simultaneous examinations because of its high number of both photometric and spectroscopic observations in the past. Here we compare changes of the dust radius to shape variations of broad emission lines (BEL). While the radius of the dust torus decreased by almost a factor of two from 2004 to 2006 shape variations can be seen in the red wing of BELs of NGC 4151. These simultaneous changes are discussed in a dust and BEL formation scheme. We also use the BEL shape variations to assess possible cloud distributions, especially in azimuthal direction, which could be responsible for the observed variations. Our findings can best be explained in the framework of a dust inflated accretion disk. The changes in the BELs suggest that this dusty cloud formation does not happen continuously, and over the whole accretion disk, but on the contrary in spatially confined areas over rather short amount of times. We derive limits to the azimuthal extension of the observed localized BEL flux enhancement event.

Rapid luminosity decline and subsequent reformation of the innermost dust distribution in the changing-look AGN Mrk 590

“…As discussed by Baskin & Laor (2018), the high temperature dust grains in the disk atmosphere provide a sufficiently large opacity of κ ∼ 10 cm 2 g −1 to vertically puff-up the disk height by radiation pressure from the local accretion disk IR emission (Czerny & Hryniewicz 2011;Czerny et al 2017;Esser et al 2019;Chelouche et al 2019). The vertical motion of the puffed-up region is governed by the balance between the radiation pressure and the SMBH gravity act-ing on the gas/dust particles, which forms a failed dusty disk wind (Czerny et al 2017).…”

The nuclear architecture of NGC 4151: on the path toward a universal outflow mechanism in light of NGC 1068

“…Furthermore, a prohibited emission would be inconceivable for such small volumes and high densities, when compared to the NLR. Therefore, we maintain the hypothesis that this emission represents an event located at the basis of the NLR and could be possibly a response to the high-velocity line profile variations detected by Esser et al (2019).…”

“…The nature of the transient emission in ( 1) is explored in Appendix A. The broad line emission, in turn, is known to vary in scales of months (Antonucci & Cohen 1983;Penston & Perez 1984;Esser et al 2019) or completely fade away (Boksenberg et al 1975 and this work).…”

“…A study concerning the temporal variation of the line profile in some IR emissions was performed by Esser et al (2019) in NGC 4151, which noted an increasing line flux ( 2 times) for a velocity interval between 2000 and 3000 km s −1 , in redshift. This variation was detected along a period of 3 years, with a peak around 2006.…”

Past, Present, and Future of the Scaling Relations of Galaxies and Active Galactic Nuclei

“…One of the main issues is whether there are indeed gas clouds or whether the broad lines are emitted directly by a continuumilluminated accretion disk (Collin-Souffrin et al, 1988;Dumont and Collin-Souffrin, 1990). If clouds are indeed present, the mechanism of confinement is unclear, although confinement by an external magnetic field is favored (Rees, 1987;Bottorff and Ferland, 2000;Chelouche and Netzer, 2001;Shadmehri, 2015;Esser et al, 2019). The quasar main sequence discussed in Section 14.2 provides a focus for these questions, but the physical processes of line-emitting gas dynamics have not yet been contextualized for different accretion modes (Section 14.3).…”