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The Sloan Digital Sky Survey Reverberation Mapping Project : biases in z > 1.46 redshifts due to quasar diversity

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Date
06/12/2016
Author
Denney, K. D.
Horne, Keith
Brandt, W. N.
Grier, C. J.
Ho, Luis C.
Peterson, B. M.
Trump, J. R.
Ge, J.
Funder
Science & Technology Facilities Council
Grant ID
ST/M001296/1
Keywords
Galaxies: active
Galaxies: distances and redshifts
Galaxies: nuclei
Quasars: emission lines
Quasars: general
Quasars: supermassive black holes
QB Astronomy
QC Physics
Astronomy and Astrophysics
Space and Planetary Science
3rd-NDAS
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Abstract
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.
Citation
Denney , K D , Horne , K , Brandt , W N , Grier , C J , Ho , L C , Peterson , B M , Trump , J R & Ge , J 2016 , ' The Sloan Digital Sky Survey Reverberation Mapping Project : biases in z > 1.46 redshifts due to quasar diversity ' , Astrophysical Journal , vol. 833 , no. 1 , 33 . https://doi.org/10.3847/1538-4357/833/1/33
Publication
Astrophysical Journal
Status
Peer reviewed
DOI
https://doi.org/10.3847/1538-4357/833/1/33
ISSN
0004-637X
Type
Journal article
Rights
© 2016. The American Astronomical Society. All rights reserved. This work is made available online in accordance with the publisher’s policies. This is the final published version of the work, which was originally published at: https://dx.doi.org/10.3847/1538-4357/833/1/33
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  • University of St Andrews Research
URI
http://hdl.handle.net/10023/10057

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