Broad-line region in active galactic nuclei: Dusty or dustless?

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Authors

PANDEY Ashwani CZERNY Bozena PANDA Swayamtrupta PRINCE Raj JAISWAL Vikram Kumar MARTINEZ-ALDAMA Mary Loli ZAJAČEK Michal SNIEGOWSKA Marzena

Year of publication 2023
Type Article in Periodical
Magazine / Source Astronomy and Astrophysics
MU Faculty or unit

Faculty of Science

Citation
Web https://www.aanda.org/articles/aa/full_html/2023/12/aa47819-23/aa47819-23.html
Doi http://dx.doi.org/10.1051/0004-6361/202347819
Keywords galaxies: active; galaxies: Seyfert; methods: numerical
Description Context. Dust in active galactic nuclei is clearly present right outside the broad-line region (BLR) in the form of a dusty molecular torus. However, some models of the BLR predict that dust may also exist within the BLR. Aims. We study the reprocessing of radiation by the BLR with the aim of observing how the presence of dust affects the reprocessed continuum and the line properties. Methods.We calculated a range of models using the CLOUDY photoionisation code for dusty and dustless plasma. We paid particular attention to the well-studied object NGC 5548, and we compared the line equivalent width predictions with the data from observations for this object. Results. We obtained a rough agreement between the expected equivalent widths of the Hß and Mg II lines and the observed values for NGC 5548 for the line distances implied by the time-delay measurement (for Hß) and the radius-luminosity relation (for Mg II) when the medium is dusty. We found the incident radiation to be consistent with the radiation seen by the observer, so no shielding between the inner disc and the BLR is required. High ionisation lines such as He II, however, clearly form in the inner dustless region. When the additional absorber is present, the Hß emitting region moves closer to the dustless part of the accretion disc surface.
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