HST/COS Observations of the Quasar HE 2347-4342: Probing the Epoch of He II Patchy Reionization at Redshifts z = 2.4-2.9

Details HST/COS Observations of the Quasar HE 2347-4342: Probing the Epoch of He II Patchy Reionization at Redshifts z = 2.4-2.9 HST/COS Observations of the Quasar HE 2347-4342: Probing the Epoch of He II Patchy Reionization at Redshifts z = 2.4-2.9

Oct 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010apj...722.1312s&link_type=abstract

The Astrophysical Journal, Volume 722, Issue 2, pp. 1312-1324 (2010).

Astronomy and Astrophysics

Astronomy

24

Dark Ages, Reionization, First Stars, Galaxies: Active, Intergalactic Medium, Quasars: Absorption Lines, Quasars: Individual: He 2347-4342, Ultraviolet: General

Scientific paper

We report ultraviolet spectra of the high-redshift (z em ≈ 2.9) quasar, HE 2347 - 4342, taken by the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope. Spectra in the G130M (medium resolution, 1135-1440 Å) and G140L (low resolution, 1030-2000 Å) gratings exhibit patchy Gunn-Peterson absorption in the 303.78 Å Lyα 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 signal-to-noise ratio (S/N), and better determined backgrounds than previous studies, with sensitivity to abundance fractions x He II ≈ 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 and range from τHe II <= 0.02 to τHe II >= 5, with a slow recovery in mean optical depth to langτHe II rang <= 2 at z < 2.7. The He II/H I optical-depth ratio varies (η≈ 10-100 for 2.4 < z < 2.73 and η = 5-500 for 2.75 < z < 2.89) on scales Δz <~ 0.01 (10.8 Mpc in comoving radial distance at z = 2.8), with numerous flux-transmission windows between 1135 and 1186 Å. The He II absorption extends to 1186.26 Å (z = 2.905), including associated absorbers with z abs ≈ z QSO and minimal "proximity effect" of flux transmission at the He II edge. We propose a QSO systemic redshift z QSO = 2.904 ± 0.002, some Δz = 0.019 higher than that derived from O I λ1302 emission. Three long troughs (4-10 Å or 25-60 Mpc comoving distance) of strong He II absorption between z = 2.75and2.90 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 He II reionization may extend to z <~ 2.7.
Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS5-26555.

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