Broad-line region geometry from multiple emission lines in a single-epoch spectrum

L. Kuhn, J. Shangguan*, R. Davies, A. W.S. Man, Y. Cao, J. Dexter, F. Eisenhauer, N. M.Förster Schreiber, H. Feuchtgruber, R. Genzel, S. Gillessen, S. Hönig, D. Lutz, H. Netzer, T. Ott, S. Rabien, D. J.D. Santos, T. Shimizu, E. Sturm, L. J. Tacconi

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


The broad-line region (BLR) of active galactic nuclei (AGNs) traces gas close to the central supermassive black hole (BH). Recent reverberation mapping (RM) and interferometric spectro-astrometry data have enabled detailed investigations of the BLR structure and dynamics as well as estimates of the BH mass. These exciting developments have motivated comparative investigations of BLR structures using different broad emission lines. In this work, we have developed a method to simultaneously model multiple broad lines of the BLR from a single-epoch spectrum. We applied this method to the five strongest broad emission lines (Hα, Hβ, Hγ, Paβ, and He i λ5876) in the UV-to-near-IR spectrum of NGC 3783, a nearby Type I AGN that has been well studied by RM and interferometric observations. Fixing the BH mass to the published value, we fit these line profiles simultaneously to constrain the BLR structure. We find that the differences between line profiles can be explained almost entirely as being due to different radial distributions of the line emission. We find that using multiple lines in this way also enables one to measure some important physical parameters, such as the inclination angle and virial factor of the BLR. The ratios of the derived BLR time lags are consistent with the expectation of theoretical model calculations and RM measurements.

Original languageEnglish
Article numberA52
JournalAstronomy and Astrophysics
StatePublished - 1 Apr 2024


FundersFunder number
Natural Sciences and Engineering Research Council of CanadaRGPIN-2021-03046
Natural Sciences and Engineering Research Council of Canada


    • galaxies: Seyfert
    • galaxies: active
    • galaxies: individual: NGC 3783
    • quasars: emission lines
    • quasars: supermassive black holes


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