2010/08/17 by J. Michael Shull, Michael Shull, Shull, Michael +8
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Cosmology and Nongalactic Astrophysics (astro-ph.CO) #FOS: Physical sciences #Galaxies: Formation, Evolution, Phenomena #astro-ph.CO
paper · pdf · doi:10.48550/arxiv.1008.2957
18 pages, 8 figures (ApJ, in press) - High-resn paper available at http://casa.colorado.edu/~mshull/HeII-paper.pdf
arxiv created 2010/08/17 · openalex publication_date 2010/08/17 · arxiv updated 2010/08/19 · openalex created_date 2019/06/27 · openalex updated_date 2026/07/28
We report ultraviolet spectra of the high-redshift (zem = 2.9) quasar, HE 2347-4342, taken by the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST). Spectra in the G130M (medium-resolution, 1135-1440 A) and G140L (low-resolution, 1030-2000 A) gratings exhibit patchy Gunn-Peterson absorption in the 303.78 A (Ly-alpha) line of He II between z = 2.39-2.87 (G140L) and z = 2.74-2.90 (G130M). With COS, we obtain better spectral resolution, higher-S/N, and better determined backgrounds than previous studies, with sensitivity to abundance fractions xHeII = 0.01 in filaments of the cosmic web. The He II optical depths from COS are higher than those with the Far Ultraviolet Spectroscopic Explorer (FUSE) and range from tauHeII < 0.02 to tauHeII > 5, with a slow recovery in mean optical depth, tau < 2 at z < 2.7. The He II/H I optical-depth ratio varies (eta = 10-100 for 2.4 < z < 2.73 and eta = 5-500 for 2.75 < z < 2.89) on scales Delta z < 0.01 (10.8 Mpc in comoving radial distance at z = 2.8), with numerous flux-transmission windows between 1135-1186 A. The He II absorption extends to 1186.26 A (z = 2.905), including associated absorbers with zabs ~ zQSO and minimal "proximity effect" of flux transmission at the He II edge. We propose a QSO systemic redshift zQSO = 2.904 +/- 0.002, some Delta z = 0.019 higher than that derived from O I (1302 A) emission. Three long troughs (4-10 A or 25-60 Mpc comoving distance) of strong He II absorption between z = 2.75-2.90 are uncharacteristic of the intergalactic medium if He II reionized at zr ~ 3. Contrary to recent indirect estimates (zr = 3.2 +/- 0.2) from H I optical depths, the epoch of HeII reionization may extend to z ~ 2.7.