The properties of broad absorption line outflows based on a large sample of quasars


Quasar outflows carry mass, momentum and energy into the surrounding environment, and have long been considered a potential key factor in regulating the growth of supermassive black holes and the evolution of their host galaxies1,2,3,4. A crucial parameter for understanding the origin of these outflows and measuring their influence on their host galaxies is the distance R between the outflow gas and the galaxy centre5,6. Although R has been measured in a number of individual galaxies7,8,9,10,11,12,13,14,15, its distribution remains unknown. Here we report the distributions of R and the kinetic luminosities of quasar outflows, using the statistical properties of broad absorption line variability in a sample of 915 quasars from the Sloan Digital Sky Survey. The mean and standard deviation of the distribution of R are 101.4±0.5 parsecs. The typical outflow distance in this sample is tens of parsecs, which is beyond the theoretically predicted location (0.01 to 0.1 parsecs) at which the accretion disk line-driven wind is launched16,17, but is smaller than the scales of most outflows that are derived using the excited-state absorption lines7,8,9,10,11,12,13,14. The typical value of the mass flow rate is tens to a hundred solar masses per year, or several times the accretion rate. The typical kinetic-to-bolometric luminosity ratio is a few per cent, indicating that outflows are energetic enough to influence the evolution of their host galaxies.

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Fig. 1: The fraction curve of BAL variabilities and the inferred recombination timescales distribution in the SDSS sample.
Fig. 2: Distributions of the properties of the BAL outflows at different ionizing parameters.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.


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We acknowledge financial support by the Strategic Priority Research Program ‘The Emergence of Cosmological Structures’ of the Chinese Academy of Sciences (XDB09000000), NSFC (NSFC-11233002, NSFC-11421303, U1431229), National Basic Research Program of China (grant number 2015CB857005), National Science Foundation of China (grant numbers 11373024, 11233003 and 11873032) and the National Key Research and Development Program of China (grant number 2017YFA0402703). Z.H. is supported by the China Scholarship Council (CSC, grant number 201706340030) during his stay at Johns Hopkins University. G.L. is supported by the National Thousand Young Talents Program of China, and acknowledges the National Natural Science Foundation of China (grant numbers 11673020 and 11421303) and the Ministry of Science and Technology of China (National Key Program for Science and Technology Research and Development, grant number 2016YFA0400700). G.M. was supported by the National Natural Science Foundation of China (grant number 11703022), and the Fundamental Research Funds for the Central Universities (grant number WK2030220017). Funding for Sloan Digital Sky Survey IV was provided by the Alfred P. Sloan Foundation, the US 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 SDSS-IV is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS Collaboration including the Brazilian Participation Group, the Carnegie Institution for Science, Carnegie Mellon University, the Chilean Participation Group, the French Participation Group, the Harvard-Smithsonian Center for Astrophysics, Instituto de Astrofísica de Canarias, Johns Hopkins University, the Kavli Institute for the Physics and Mathematics of the Universe (IPMU) / University of Tokyo, Lawrence Berkeley National Laboratory, the Leibniz Institut für Astrophysik Potsdam (AIP), the Max-Planck-Institut für Astronomie (MPIA Heidelberg), the Max-Planck-Institut für Astrophysik (MPA Garching), the Max-Planck-Institut für Extraterrestrische Physik (MPE), the National Astronomical Observatories of China, New Mexico State University, New York University, University of Notre Dame, Observatário Nacional/MCTI, The Ohio State University, Pennsylvania State University, Shanghai Astronomical Observatory, the United Kingdom Participation Group, Universidad Nacional Autónoma de México, University of Arizona, University of Colorado Boulder, University of Oxford, University of Portsmouth, University of Utah, University of Virginia, University of Washington, University of Wisconsin, Vanderbilt University and Yale University. (Note that the author initials match those in the author list, so the diphthong initials have been removed.)

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Z.H. presented the idea, made the calculations and wrote the manuscript. T.W., G.L., H.W., W.B., G.M., H.Z. and R.G. discussed the idea and the calculations. Y.X., K.T., T.W., G.L. and J.X. revised the manuscript. All authors discussed and commented on the contents of the paper.

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Correspondence to Zhicheng He or Tinggui Wang or Guilin Liu.

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He, Z., Wang, T., Liu, G. et al. The properties of broad absorption line outflows based on a large sample of quasars. Nat Astron 3, 265–271 (2019).

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