TY - JOUR
T1 - The evolution of chemical abundance in quasar broad line region
AU - Xu, Fei
AU - Bian, Fuyan
AU - Shen, Yue
AU - Zuo, Wenwen
AU - Fan, Xiaohui
AU - Zhu, Zonghong
N1 - Funding Information:
We thank Fred Hamann and the anonymous referee for comments that significantly improved the work, and Tohru Nagao for useful discussions. FX gratefully acknowledges the support from the undergraduate research programme funding of BeijingNormalUniversity. YS acknowledges support from an Alfred P. Sloan Research Fellowship and NSF grant AST-1715579. Funding for the SDSS 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. 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, Harvard-Smithsonian Center for Astrophysics, Instituto de Astrofísica de Canarias, The Johns Hopkins University, Kavli Institute for the Physics and Mathematics of the Universe (IPMU)/University of Tokyo, Lawrence Berkeley National Laboratory, Leibniz Institut für Astrophysik Potsdam (AIP), Max-Planck-Institut für Astronomie (MPIA Heidelberg), Max-Planck-Institut für Astrophysik (MPA Garching), Max-Planck-Institut für Extraterrestrische Physik (MPE), 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, 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 ofVirginia, University ofWashington, University ofWisconsin, Vanderbilt University, and Yale University.
Publisher Copyright:
© 2018 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society.
PY - 2018/10/11
Y1 - 2018/10/11
N2 - We study the relation between the metallicity of quasar broad line region (BLR) and black hole (BH) mass (107.5-1010M⊙) and quasar bolometric luminosity (1044.6-1048 erg s-1) using a sample of ~130 000 quasars at 2.25 ≤ z ≤ 5.25 from Sloan Digital Sky Survey Data Release 12 (DR12). We generate composite spectra by stacking individual spectra in the same BH mass (bolometric luminosity) and redshift bins and then estimate the metallicity of quasar BLR using metallicity-sensitive broad emission-line flux ratios based on the photoionization models. We find a significant correlation between quasar BLR metallicity and BH mass (bolometric luminosity) but no correlation between quasar BLR metallicity and redshift. We also compare the metallicity of quasar BLR and that of host galaxies inferred from the mass- metallicity relation of star-forming galaxy at z ~ 2.3 and 3.5. We find quasar BLR metallicity is 0.3 ~ 1.0 dex higher than their host galaxies. This discrepancy cannot be interpreted by the uncertainty due to different metallicity diagnostic methods, mass-metallicity relation of galaxy, metallicity gradient in quasar host galaxies, BH mass estimation, the effect of different spectral energy distribution models, and a few other potential sources of uncertainties. We propose a possibility that the high metallicity in quasar BLR might be caused by metal enrichment from massive star formation in the nucleus region of quasars or even the accretion disc.
AB - We study the relation between the metallicity of quasar broad line region (BLR) and black hole (BH) mass (107.5-1010M⊙) and quasar bolometric luminosity (1044.6-1048 erg s-1) using a sample of ~130 000 quasars at 2.25 ≤ z ≤ 5.25 from Sloan Digital Sky Survey Data Release 12 (DR12). We generate composite spectra by stacking individual spectra in the same BH mass (bolometric luminosity) and redshift bins and then estimate the metallicity of quasar BLR using metallicity-sensitive broad emission-line flux ratios based on the photoionization models. We find a significant correlation between quasar BLR metallicity and BH mass (bolometric luminosity) but no correlation between quasar BLR metallicity and redshift. We also compare the metallicity of quasar BLR and that of host galaxies inferred from the mass- metallicity relation of star-forming galaxy at z ~ 2.3 and 3.5. We find quasar BLR metallicity is 0.3 ~ 1.0 dex higher than their host galaxies. This discrepancy cannot be interpreted by the uncertainty due to different metallicity diagnostic methods, mass-metallicity relation of galaxy, metallicity gradient in quasar host galaxies, BH mass estimation, the effect of different spectral energy distribution models, and a few other potential sources of uncertainties. We propose a possibility that the high metallicity in quasar BLR might be caused by metal enrichment from massive star formation in the nucleus region of quasars or even the accretion disc.
KW - Galaxies: abundances
KW - Galaxies: active
KW - Galaxies: high redshift
KW - Quasars: emission lines
UR - http://www.scopus.com/inward/record.url?scp=85052554128&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85052554128&partnerID=8YFLogxK
U2 - 10.1093/mnras/sty1763
DO - 10.1093/mnras/sty1763
M3 - Article
AN - SCOPUS:85052554128
VL - 480
SP - 345
EP - 357
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
SN - 0035-8711
IS - 1
ER -