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标题：Accurate spectroscopic redshift of the multiply lensed quasar PSOJ0147 from the Pan-STARRS survey
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作者：C.-H. Lee ; C.-H. Lee
期刊名称：Astronomy & Astrophysics
印刷版ISSN：0004-6361
电子版ISSN：1432-0746
出版年度：2017
卷号：605
页码：1-4
DOI：10.1051/0004-6361/201731695
语种：English
出版社：EDP Sciences
摘要：Context. The gravitational lensing time delay method provides a one-step determination of the Hubble constant (H0) with an uncertainty level on par with the cosmic distance ladder method. However, to further investigate the nature of the dark energy, a H0 estimate down to 1% level is greatly needed. This requires dozens of strongly lensed quasars that are yet to be delivered by ongoing and forthcoming all-sky surveys. Aims. In this work we aim to determine the spectroscopic redshift of PSOJ0147, the first strongly lensed quasar candidate found in the Pan-STARRS survey. The main goal of our work is to derive an accurate redshift estimate of the background quasar for cosmography. Methods. To obtain timely spectroscopically follow-up, we took advantage of the fast-track service programme that is carried out by the Nordic Optical Telescope. Using a grism covering 3200−9600 Å, we identified prominent emission line features, such as Lyα, N V, O I, C II, Si IV, C IV, and [C III] in the spectra of the background quasar of the PSOJ0147 lens system. This enables us to determine accurately the redshift of the background quasar. Results. The spectrum of the background quasar exhibits prominent absorption features bluewards of the strong emission lines, such as Lyα, N V, and C IV. These blue absorption lines indicate that the background source is a broad absorption line (BAL) quasar. Unfortunately, the BAL features hamper an accurate determination of redshift using the above-mentioned strong emission lines. Nevertheless, we are able to determine a redshift of 2.341 ± 0.001 from three of the four lensed quasar images with the clean forbidden line [C III]. In addition, we also derive a maximum outflow velocity of ~9800 km s-1 with the broad absorption features bluewards of the C IV emission line. This value of maximum outflow velocity is in good agreement with other BAL quasars.
关键词：engravitational lensing: strongquasars: generalcosmology: observations