Testing AGN outflow and accretion models with C IV and He II emission line demographics in z ≈ 2 quasars

Matthew J. Temple, James H. Matthews, Paul C. Hewett, Amy L. Rankine, Gordon T. Richards, Manda Banerji, Gary J. Ferland, Christian Knigge, Matthew Stepney

Research output: Contribution to journalArticlepeer-review

3 Scopus citations


Using ≈190 000 spectra from the 17th data release of the Sloan Digital Sky Survey (SDSS), we investigate the ultraviolet emission line properties in z ≈ 2 quasars. Specifically, we quantify how the shape of C IV λ1549 and the equivalent width (EW) of He II λ1640 depend on the black hole mass and Eddington ratio inferred from Mg II λ2800. Above L/LLEdd ≤ 0.2, there is a strong mass dependence in both C IV blueshift and He II EW. Large C IV blueshifts are observed only in regions with both high mass and high accretion rate. Including X-ray measurements for a subsample of 5000 objects, we interpret our observations in the context of AGN accretion and outflow mechanisms. The observed trends in He II and 2 keV strength are broadly consistent with theoretical QSOSED models of AGN spectral energy distributions (SEDs) for low spin black holes, where the ionizing SED depends on the accretion disc temperature and the strength of the soft excess. High spin models are not consistent with observations, suggesting SDSS quasars at z ≈ 2 may in general have low spins. We find a dramatic switch in behaviour at L/LEdd ≤ 0.1: the ultraviolet emission properties show much weaker trends, and no longer agree with QSOSED predictions, hinting at changes in the structure of the broad line region. Overall, the observed emission line trends are generally consistent with predictions for radiation line driving where quasar outflows are governed by the SED, which itself results from the accretion flow and hence depends on both the SMBH mass and accretion rate.

Original languageEnglish
Pages (from-to)646-666
Number of pages21
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
StatePublished - Jul 1 2023

Bibliographical note

Funding Information:
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 .

Funding Information:
MJT acknowledges support from a FONDECYT postdoctoral fellowship (3220516). JHM acknowledges funding from the Royal Society. ALR acknowledges support from UKRI (MR/T020989/1). This work made use of astropy (Astropy Collaboration , , ), matplotlib (Hunter ), and numpy (Harris et al. ).

Publisher Copyright:
© 2023 The Author(s).


  • quasars: emission lines

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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