Ten More New Sightlines for the Study of Intergalactic Helium, and
  Hundreds of Far-UV-Bright Quasars, from SDSS, GALEX, and HST
  Absorption along quasar sightlines remains among the most sensitive direct
measures of HeII reionization in much of the intergalactic medium (IGM). Until
recently, fewer than a half-dozen unobscured quasar sightlines suitable for the
HeII Gunn-Peterson test were known; although these handful demonstrated great
promise, the small sample size limited confidence in cosmological inferences.
We have recently added nine more such clean HeII quasars, exploiting SDSS
quasar samples, broadband UV imaging from GALEX, and high-yield UV
spectroscopic confirmations from HST. Here we markedly expand this approach by
cross-correlating SDSS DR7 and GALEX GR4+5 to catalog 428 SDSS and 165 other
quasars with z>2.78 having likely (~70%) GALEX detections, suggesting they are
bright into the far-UV. Reconnaissance HST Cycle 16 Supplemental prism data for
29 of these new quasar-GALEX matches spectroscopically confirm 17 as indeed
far-UV bright. At least 10 of these confirmations have clean sightlines all the
way down to HeII Lyman-alpha, substantially expanding the number of known clean
HeII quasars, and reaffirming the order of magnitude enhanced efficiency of our
selection technique. Combined confirmations from this and our past programs
yield more than twenty HeII quasars, quintupling the sample. These provide
substantial progress toward a sample of HeII quasar sightlines large enough,
and spanning a sufficient redshift range, to enable statistical IGM studies
that may avoid individual object peculiarity and sightline variance. Our
expanded catalog of hundreds of high-likelihood far-UV-bright QSOs additionally
will be useful for understanding the extreme-UV properties of the quasars
themselves.
