2023/03/28 by Keiichi Wada, Wada, Keiichi, Y. Kudoh +3 · 2 citations
Engineering · Physics and Astronomy · #Astrophysical Phenomena and Observations #Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #Galaxies: Formation, Evolution, Phenomena #Heat Transfer Mechanisms
paper · pdf · doi:10.48550/arxiv.2303.16360
openalex publication_date 2023/03/28 · openalex created_date 2023/04/05 · openalex updated_date 2026/07/28
Multi-wavelength observations of active galactic nuclei (AGNs) often reveal various time scales of variability. Among these phenomena, "changing-look AGNs" are extreme cases where broad emission lines become faint/bright or even disappear/emerge between multi-epoch observations, providing crucial information about AGN internal structures. We here focus on "changing-state" AGNs, specifically investigating the transition of optical spectra over years to tens of years. Based on the axisymmetric radiation-hydrodynamical simulations (Paper I) for the gas dynamics within the dust-sublimation radius, we investigate the spectral properties of ionized gas exposed to the radiation from an AGN with a 107 Msun supermassive black hole. We find significant time-dependent variations in the Balmer emission lines by utilizing post-process pseudo-three-dimensional calculations and the spectral synthesis code CLOUDY. The equivalent width of Halpha and Hbeta changes by a factor of 3, or the emission lines even disappear during 30 years for the same viewing angle. The time-dependent behaviour arises primarily from gas dynamics, particularly the formation of non-steady, radiation-driven outflows within the innermost region of the disc (r <10-3 pc). The intricate interplay between non-spherical radiation sources at the core of AGNs and the dynamic behavior of gas within the dust sublimation radius gives rise to radiation-driven outflows. This non-steady outflow potentially contributes to the observed variability in Balmer line emissions over multi-year timescales in certain AGNs.