CAOSP abstracts, Volume: 56, No.: 1, year: 2026

Author(s): Ochmann, M.W.; Probst, M.A.; Kollatschny, W.; Diehl, L.; Cackett, E.M.; Chelouche, D.; Chini, R.; Grupe, D.; Haas, M.; Horne, K.; Kaspi, S.; Komossa, S.
Journal: Contributions of the Astronomical Observatory Skalnaté Pleso, vol. 56, no. 1, p. 102-111.
Date: 01/2026
Title: Ca II and O I as precision probes of the broad-line region in AGN
Keyword(s): NGC 4593, active galactic nuclei, broad-line region, double-peaked emitter, reverberation mapping
Pages: 102 -- 111
DOI: https://doi.org/10.31577/caosp.2026.56.1.102
NASA ADS Abstract Service: 2026CoSka..56a.102O
Citation:
License: This work is licensed under a Creative Commons Attribution 4.0 International License

Abstract: Ca II and O I emission lines in active galactic nuclei (AGN) have been used as powerful diagnostic probes of the broad-line region (BLR) for the past 40 years. In particular, line ratio diagnostics have been used to constrain the physical conditions in the low-ionization phase of the BLR, while line width measurements have provided rough constraints on the location of the emission region relative to the Balmer-emitting phase of the BLR. However, due to limited observational capabilities, detailed line-profile studies of these lines--directly linking Ca II and O I with structural BLR models--have only become possible very recently. Here, we present an overview of our most recent study that has enabled investigations of Ca II and O I emission lines in unprecedented detail, directly linking Ca II triplet emission profiles to the kinematics of a rotating disk. We focus on our results for NGC 4593, but we also provide an outlook on how Ca II and O I open up a new observational window to probe the low-ionization part of the BLR in general.