Recent improvements to atomic energy-level data allow, for the first time, accurate predictions to be made for the Fe iii line emission strengths in the spectra of luminous, Lbol≃ 1046-1048 ergs-1, active galactic nuclei. The Fe iii emitting gas must be primarily photoionized, consistent with observations of line reverberation. We use cloudy models exploring a wide range of parameter space, together with ∼26 000 rest-frame ultraviolet spectra from the Sloan Digital Sky Survey, to constrain the physical conditions of the line emitting gas. The observed Fe iii emission is best accounted for by dense (nH ∼1014 cm-3) gas which is microturbulent, leading to smaller line optical depths and fluorescent excitation. Such high density gas appears to be present in the central regions of the majority of luminous quasars. Using our favoured model, we present theoretical predictions for the relative strengths of the Fe iii UV34 λλ1895, 1914, 1926 multiplet. This multiplet is blended with the Si iii] λ1892 and C iii] λ1909 emission lines and an accurate subtraction of UV34 is essential when using these lines to infer information about the physics of the broad line region in quasars.
|Number of pages||12|
|Journal||Monthly Notices of the Royal Astronomical Society|
|State||Published - Jun 17 2020|
Bibliographical noteFunding Information:
We thank the anonymous referee for a thoughtful report which led to improved clarity in many parts of the manuscript. It is a pleasure to note useful comments from Bob Carswell, Gordon Richards, and Hagai Netzer. MJT and ALR thank the Science and Technology Facilities Council (STFC) for the award of studentships. GJF acknowledges support by the National Science Foundation (1816537), NASA (ATP 17-ATP17-0141), and the Space Telescope Science Institute (HST-AR-15018). PCH acknowledges funding from STFC via the Institute of Astronomy, Cambridge, Consolidated Grant. CPB acknowledges support through R1711APL : QUB Astronomy Observation and Theory Consolidated Grant. NRB is funded by STFC Grant ST/R000743/1 with the University of Strathclyde. This work made use of Astropy (Astropy Collaboration et al. 2013; Price-Whelan et al. 2018), Matplotlib (Hunter 2007), and corner.py (Foreman-Mackey 2016).
Funding for the Sloan Digital Sky Survey IV has been provided by the Alfred P. Sloan Foundation, the U.S. Department of Energy Office of Science, and the Participating Institutions. SDSS-IV acknowledges support and resources from the Center for High-Performance Computing at the University of Utah. The SDSS web site is www.sdss.org.
© 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.
- atomic data
- quasars: emission lines
- quasars: general
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science