PI: David Syphers, University of Colorado, Boulder, David.Syphers@colorado.edu
Address: Astrophysics and Planetary Sciences, 389 UCB, Boulder, CO 80309, USA
CoI: Scott F. Anderson, University of Washington, Seattle
CoI: Wei Zheng, Johns Hopkins University
Title: Finding an Accurate Redshift for a Unique He II Quasar
Abstract: The epoch of helium reionization ended at z$~2.7-2.9, and likely began at z$~3.5-4.5. The most direct probe of the end of this epoch is the Gunn-Peterson test, where substantial He \sc ii fractions absorb all He \sc ii Ly(alpha) photons locally at 304 \AA, leaving dark troughs in the spectra of high-redshift quasars. Near the beginning of helium reionization, high He \sc ii fractions can lead to a damping wing of absorption extending redward of (1+z_\rm QSO) \times 304 \AA. Even in the absence of a red wing, the line-of- sight proximity effect reveals a wealth of data on the IGM and quasar physics. However, all such studies require the precise systemic redshift of the quasar in question. We propose to obtain a precise redshift to the uniquely bright and high-redshift He \sc ii quasar SDSS0915+4756, in support of an approved HST observation. Extant optical spectroscopy tells us the quasar is z$~eq3.34, but this is based on high-ionization broad emission lines that can be systematically shifted by thousands of km s^-1. NIR K-band spectroscopy of H(beta) and [O III] 5007 emission will conclusively determine the redshift.
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