2016/06/08 by Liam Coatman, P. C. Hewett, Paul C. Hewett +3 · 121 citations
Physics and Astronomy · #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Black hole (networking) #Blueshift #Emission spectrum #Galaxies: Formation, Evolution, Phenomena #Galaxy #Gamma-ray bursts and supernovae #Line (geometry) #Luminosity #Optics #Physics #Quasar #Redshift #Spectral line #Virial mass #Virial theorem #astro-ph.GA
paper · pdf · doi:10.1093/mnras/stw1360
published in Monthly Notices of the Royal Astronomical Society 461(1), 647-665 (Oxford University Press) · Accepted for publication in MNRAS (21 pages, 11 figures, 4 tables)
arxiv created 2016/06/08 · openalex publication_date 2016/06/09 · openalex created_date 2016/06/24 · arxiv updated 2016/07/27 · openalex updated_date 2026/08/05
Black hole masses are crucial to understanding the physics of the connection between quasars and their host galaxies and measuring cosmic black hole-growth. At high redshift, z ≳ 2.1, black hole masses are normally derived using the velocity width of the C iv|\tt λ λ|1548, 1550 broad emission line, based on the assumption that the observed velocity widths arise from virial-induced motions. In many quasars, the C iv emission line exhibits significant blue asymmetries (‘blueshifts’) with the line centroid displaced by up to thousands of km s−1 to the blue. These blueshifts almost certainly signal the presence of strong outflows, most likely originating in a disc wind. We have obtained near-infrared spectra, including the Hα |\tt λ|6565 emission line, for 19 luminous (LBol = 46.5–47.5 erg s−1) Sloan Digital Sky Survey quasars, at redshifts 2 < z < 2.7, with C iv emission lines spanning the full range of blueshifts present in the population. A strong correlation between C iv velocity width and blueshift is found and, at large blueshifts, >2000 km s−1, the velocity widths appear to be dominated by non-virial motions. Black hole masses, based on the full width at half-maximum of the C iv emission line, can be overestimated by a factor of 5 at large blueshifts. A larger sample of quasar spectra with both C iv and H β, or Hα, emission lines will allow quantitative corrections to C iv-based black hole masses as a function of blueshift to be derived. We find that quasars with large C iv blueshifts possess high Eddington luminosity ratios and that the fraction of high-blueshift quasars in a flux-limited sample is enhanced by a factor of approximately 4 relative to a sample limited by black hole mass.