Broad He I 1.08-mu m absorption from the obscurer in the active galaxy NGC 5548

0550187 - ASÚ 2022 RIV GB eng J - Journal Article
Wildy, C. - Landt, H. - Ward, M. J. - Czerny, B. - Kynoch, Daniel
Broad He I 1.08-mu m absorption from the obscurer in the active galaxy NGC 5548.
Monthly Notices of the Royal Astronomical Society. Roč. 500, č. 2 (2021), s. 2063-2075. ISSN 0035-8711. E-ISSN 1365-2966
Institutional support: RVO:67985815
Keywords : quasars * absorption lines * galaxies: Seyfert
OECD category: Astronomy (including astrophysics,space science)
Impact factor: 5.235, year: 2021
Method of publishing: Limited access
https://doi.org/10.1093/mnras/staa3301

The nucleus of the active galaxy NGC 5548 was the target of two intensive spectroscopic monitoring campaigns at X-ray, ultraviolet (UV), and optical frequencies in 2013/2014. These campaigns detected the presence of a massive obscuration event. In 2016/2017, Landt et al. conducted a near-IR spectroscopic monitoring campaign on NGC 5548 and discovered He I 1.08-mu m absorption. Here, we decompose this absorption into its components and study its time variability. We attribute the narrow He I absorption lines to the warm absorber (WA) and, as for the newly appeared low-ionization WA lines in the UV, their presence is most likely due to a reduction in ionization parameter caused by the obscurer. The observed variability of the narrow He I absorption is consistent with what is expected for the WA. Most importantly, we also detect fast, broad He I absorption, which we attribute to the obscurer. This He I broad absorption, which is indicative of a high column density gas, is unsaturated and variable on time-scales of a few months. The observed variability of the obscurer is mainly due to changes in ionization, although density changes also play a role. We test the physical cycle model of Dehghanian et al. which proposes that helium recombination can account for how the obscurer influences the physics of the WA gas. Our results support their model, but also indicate that the reality might be more complex.
Permanent Link: http://hdl.handle.net/11104/0325972