FUSE and HST Observations of Helium II Absorption in the IGM: Implications for Seeing HI Re-ionization Gerard Kriss STScI

What We Can Learn from Observations of He II Absorption  Use the ratio of He II and H I column densities to ascertain the shape of the ionizing spectrum.  Do stars or quasars dominate the radiation field at z=2-3?  Using the spectral shape in conjunction with proximity-effect measurements of the radiation field intensity,  Set limits on the escape fraction of radiation from star-forming galaxies.  Trace the qualitative appearance of He II reionization.  This may serve as a preview of what H I reionization looks like. A red damping wing on the G-P trough? Proximity zone on the blue side of the trough edge? Red-shifted absorption features indicative of infalling clouds?

Quasars with He II Absorption QuasarZVObserved with: Q FOC, GHRS, STIS HS HUT, FOS, GHRS, STIS, FUSE HE 2347  FOS, GHRS, STIS, FUSE PKS 1935  GHRS, FOS SDSS 2346  STIS, ACS SDSS STIS SDSS STIS Q STIS  Difficult to see  at z~3, only 15% of sightlines are free of LLSs.  There are only 8 known quasars with clear lines of sight:

Indirect Indicators of He II Reionization  Observations of the end stages of He II reionization: HE : Reimers et al. (1997), Smette et al. (2002), Zheng et al. (2004a).  Si IV/C IV decreases at z~3: Songaila (1998; 2005).  HI line widths increase  IGM temperature increases at z~3.3: Theuns et al. (2002).  HI opacity decreases at z~3.3: Bernardi et al. (2003).

He II Optical Depth vs. Redshift Davidsen et al Smette et al Zheng et al. 2004a Fechner et al. 2006

The Transition to Complete Reionization Redshift  Ly  Razoumov et al. 2002

Indirect Indicators of He II Reionization  Observations of the end stages of He II reionization: HE : Reimers et al. (1997), Smette et al. (2002), Zheng et al. (2004a).  Si IV/C IV decreases at z~3: Songaila (1998; 2005).  HI line widths increase  IGM temperature increases at z~3.3: Theuns et al. (2002).  HI opacity decreases at z~3.3: Bernardi et al. (2003).

Ionization Evolution of the IGM Songaila 2005 (see also 1998)

Indirect Indicators of He II Reionization  Observations of the end stages of He II reionization: HE : Reimers et al. (1997), Smette et al. (2002), Zheng et al. (2004a).  Si IV/C IV decreases at z~3: Songaila (1998; 2005).  HI line widths increase  IGM temperature increases at z~3.3: Theuns et al. (2002).  HI opacity decreases at z~3.3: Bernardi et al. (2003).

Thermal History of the IGM Theuns et al. 2002

Indirect Indicators of He II Reionization  Observations of the end stages of He II reionization: HE : Reimers et al. (1997), Smette et al. (2002), Zheng et al. (2004a).  Si IV/C IV decreases at z~3: Songaila (1998; 2005).  HI line widths increase  IGM temperature increases at z~3.3: Theuns et al. (2002).  HI opacity decreases at z~3.3: Bernardi et al. (2003).

Opacity Evolution of the HI Ly  Forest Bernardi et al. 2003

IGM Optically Thick In He II Ly  Extrapolated Continuum Transparent Windows IGM Transparent in He II Ly  Kriss et al FUSE Spectrum of HE (376 ks)

FUSE He II Absorption  Keck H I Kriss et al. 2001

STIS & FUSE Spectra of HS Fechner et al STIS Spectrum: G140L + G230L Best-fit continuum with E(B-V)=0.025 FUSE Spectrum: 290 ks

Starlight Quasar Illumination  (N HeII /N HI ) vs. Redshift (z) Zheng et al. 2004a

Constraining F esc for Star-forming Galaxies Scott et al Bianchi et al Scott et al Kriss & Scott 2006

He II Absorption in SDSS QSOs STIS Low-resolution snapshots (G140L), 600 s (Zheng et al. 2004b) z = 3.49 z = 3.81 z = 3.83

Simulated He II Lyman Trough “Cosmic voids” produced by local ionizing sources Gunn-Peterson trough Proximity profile Red damping wing He II Ly  forest

 FUSE observations of HE2347–4342 and HS resolve the He II Ly  forest.  He II / H I opacity ratios indicate that AGN contribute more than 50% of the ionizing UV flux at z=2.5.  This implies that the escape fraction for radiation from star-forming galaxies must be less than 5%.  STIS snapshots have identified 3 quasars at redshifts likely to be beyond He II reionization.  Future observations with COS of these quasars may give spectral clues to the qualitative appearance of H I reionization. Conclusions