The restless nature of AGN: 10 years later

Broad spectral line variability of the changing-look AGN NGC 3516: Role of a dusty broad line region

29 giu 2023, 16:15

15m

Aula Magna (Centro Congressi Federico II)

Contributed talk Extreme variability: CL AGN, TDEs and binary SMBHs

Description

Here we present our study of the variability of the broad Hbeta line profile of the "changing look" active galactic nucleus (CL-AGN) NGC 3516 over a long period (from 1996 to 2021).
We model the broad line profiles assuming that there is emission from the accretion disc superposed with emission from a surrounding region that is outside the disc.
We find that in the Type 1 activity phase (i.e., when the strong broad emission lines are observed), the broad line region (BLR) is very complex. There is a clear disc-like BLR contributing to the broad line wings and an additional intermediate line region (ILR) contributing to the line core. In the high activity phase, the ILR emission is close to the center of the line (slightly shifted to red in some cases), whereas in the low activity phase (i.e., Type 2 phase), the ILR component is clearly shifted to blue, indicating outflow.
At different activity stages, the complex BLR structure can be detected, indicating that the gas motion remains constant but the line emission becomes weak. This may be caused by dust entering the interior of the BLR during the low activity stage, forming a dusty BLR. This leads to a decrease in ionization and recombination rates, so that the broad lines almost disappear.