TY - JOUR
T1 - THE SLOAN DIGITAL SKY SURVEY REVERBERATION MAPPING PROJECT
T2 - BIASES in z > 1.46 REDSHIFTS DUE to QUASAR DIVERSITY
AU - Denney, K. D.
AU - Horne, Keith
AU - Brandt, W. N.
AU - Grier, C. J.
AU - Ho, Luis C.
AU - Peterson, B. M.
AU - Trump, J. R.
AU - Ge, J.
N1 - Funding Information:
K.D.D. is supported by an NSF AAPF fellowship awarded under NSF grant AST-1302093. K.H. acknowledges support from STFC grant ST/M001296/1. W.N.B. acknowledges support from NSF grant AST-1516784. C.J.G. acknowledges support from NSF grant AST-1517113. B.M.P. is grateful for support from NSF grant AST-1008882. K.H. acknowledges support from STFC grant ST/M001296/1. L.C.H. thanks Carnegie Observatories for providing telescope access and acknowledges financial support from Peking University, the Kavli Foundation, the Chinese Academy of Science through grant No. XDB09030102 (Emergence of Cosmological Structures) from the Strategic Priority Research Program, and from the National Natural Science Foundation of China through grant No. 11473002. J.R.T. acknowledges support from NASA through Hubble Fellowship grant #51330 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA under contract NAS 5-26555. Funding for SDSS-III has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, and the U.S. Department of Energy Office of Science.
Publisher Copyright:
© 2016. The American Astronomical Society. All rights reserved.
PY - 2016/12/10
Y1 - 2016/12/10
N2 - We use the coadded spectra of 32 epochs of Sloan Digital Sky Survey (SDSS) Reverberation Mapping Project observations of 482 quasars with z > 1.46 to highlight systematic biases in the SDSS- and Baryon Oscillation Spectroscopic Survey (BOSS)-pipeline redshifts due to the natural diversity of quasar properties. We investigate the characteristics of this bias by comparing the BOSS-pipeline redshifts to an estimate from the centroid of He ii λ1640. He ii has a low equivalent width but is often well-defined in high-S/N spectra, does not suffer from self-absorption, and has a narrow component which, when present (the case for about half of our sources), produces a redshift estimate that, on average, is consistent with that determined from [O ii] to within the He ii and [O ii] centroid measurement uncertainties. The large redshift differences of ∼1000 km s-1, on average, between the BOSS-pipeline and He ii-centroid redshifts, suggest there are significant biases in a portion of BOSS quasar redshift measurements. Adopting the He ii-based redshifts shows that C iv does not exhibit a ubiquitous blueshift for all quasars, given the precision probed by our measurements. Instead, we find a distribution of C iv-centroid blueshifts across our sample, with a dynamic range that (i) is wider than that previously reported for this line, and (ii) spans C iv centroids from those consistent with the systemic redshift to those with significant blueshifts of thousands of kilometers per second. These results have significant implications for measurement and use of high-redshift quasar properties and redshifts, and studies based thereon.
AB - We use the coadded spectra of 32 epochs of Sloan Digital Sky Survey (SDSS) Reverberation Mapping Project observations of 482 quasars with z > 1.46 to highlight systematic biases in the SDSS- and Baryon Oscillation Spectroscopic Survey (BOSS)-pipeline redshifts due to the natural diversity of quasar properties. We investigate the characteristics of this bias by comparing the BOSS-pipeline redshifts to an estimate from the centroid of He ii λ1640. He ii has a low equivalent width but is often well-defined in high-S/N spectra, does not suffer from self-absorption, and has a narrow component which, when present (the case for about half of our sources), produces a redshift estimate that, on average, is consistent with that determined from [O ii] to within the He ii and [O ii] centroid measurement uncertainties. The large redshift differences of ∼1000 km s-1, on average, between the BOSS-pipeline and He ii-centroid redshifts, suggest there are significant biases in a portion of BOSS quasar redshift measurements. Adopting the He ii-based redshifts shows that C iv does not exhibit a ubiquitous blueshift for all quasars, given the precision probed by our measurements. Instead, we find a distribution of C iv-centroid blueshifts across our sample, with a dynamic range that (i) is wider than that previously reported for this line, and (ii) spans C iv centroids from those consistent with the systemic redshift to those with significant blueshifts of thousands of kilometers per second. These results have significant implications for measurement and use of high-redshift quasar properties and redshifts, and studies based thereon.
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U2 - 10.3847/1538-4357/833/1/33
DO - 10.3847/1538-4357/833/1/33
M3 - Article
AN - SCOPUS:85006701088
VL - 833
JO - Astrophysical Journal
JF - Astrophysical Journal
SN - 0004-637X
IS - 1
M1 - 33
ER -