Query : 1997A&A...327..890R

1997A&A...327..890R - Astronomy and Astrophysics, volume 327, 890-900 (1997/11-3)

Patchy intergalactic HeII absorption in HE 2347-4342. The possible discovery of the epoch of He-reionization.


Abstract (from CDS):

We report on observations of redshifted HeII303.8Å absorption in the high-redshift QSO HE2347-4342 (z=2.885, V=16.1) with the Goddard High Resolution Spectrograph on board HST in its low resolution mode ({DELTA}λ=0.7Å). With fλ=3.6x10–15erg/cm2/s/Å at the expected position of HeII304 Å absorption it is the most UV-bright high redshift QSO discovered so far. We show that the HeII opacity as a function of redshift is patchy showing spectral regions with low HeII opacity (``voids'') and regions with high HeII opacity (blacked-out ``troughs'') and no detectable flux. Combination with high-resolution optical spectra of the Lyα forest using CASPEC at the 3.6m telescope shows that the voids can be explained either exclusively by Lyα forest cloud absorption with a moderate NHeII/NHI ratio η≤100 and turbulent line broadening or by a combination of Lyα forest with η=45 and thermal broadening plus a diffuse medium with τGPHeII≃0.3. Since the latter is a minimum assumption for the Lyα forest, a strict upper limit to a diffuse medium is {OMEGA}diff<0.02 h50–1.5 at z=2.8. In the troughs in addition to the Lyα forest opacity a continuous HeII 304Å opacity τ= 4.8+∞–2 is required. In case of photoionization, the troughs would require a diffuse component with a density close to {OMEGA} ≃0.077(η/45)–0.5 h50–1.5, i.e. all baryons in the universe, which is inconsistent, however, with the observed absence of such a component in the voids. A tentative interpretation is that we observe the epoch of partial HeII reionization of the universe with patches not yet reionized. In that case a diffuse component with {OMEGA}diff≥1.3x10–4h–150 would be sufficient to explain the ``trough'' opacity. The size of the 1163-1172Å trough is ∼6h50–1 Mpc or ∼2300km/s, respectively. We also discuss partially resolved HeII absorption of a high-ionization associated absorption system. Despite its high luminosity HE 2347-4342 does not show a HeII proximity effect. A possible reason is that the strong associated system shields the HeII ionizing continuum.

Abstract Copyright:

Journal keyword(s): quasars: individual: HE 2347-4342 - quasars: absorption lines - cosmology: observations

Simbad objects: 4

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Number of rows : 4
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2022
1 LBQS 0302-0019 QSO 03 04 49.8593341368 -00 08 13.534398816   18.08 17.80 17.5   ~ 246 0
2 HS 1700+6416 QSO 17 01 00.6194059368 +64 12 09.118892376   16.39 16.17     ~ 360 0
3 QSO B1935-692 QSO 19 40 25.5281346264 -69 07 56.972724240   18.36 18.8     ~ 108 1
4 QSO B2347-4342 QSO 23 50 34.2593744544 -43 25 59.683985652   16.3 16.3     ~ 165 0

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