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 Observationsof 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

Quasar Z V Observed with:

Q 0302-003 3.29 17.8 FOC, GHRS, STIS

HS 1700+64 2.74 16.1 HUT, FOS, GHRS, STIS, FUSE

HE 234743 2.89 16.3 FOS, GHRS, STIS, FUSE

PKS 193569 3.18 17.3 GHRS, FOS

SDSS 234600 3.49 17.5 STIS, ACS

SDSS 1711+60 3.83 19.4 STIS

SDSS 1614+48 3.81 19.6 STIS

Q 1157+31 2.97 17 STIS

Difficult to seeat 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: HE2347-4342: 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. 1996Smette et al. 2002Zheng et al. 2004aFechner 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: HE2347-4342: 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: HE2347-4342: 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: HE2347-4342: 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 ThickIn He II Ly

ExtrapolatedContinuum

TransparentWindows

IGM Transparent in He II Ly

Kriss et al. 2001

FUSE Spectrum of HE2347-4342

(376 ks)

FUSE He II Absorption Keck H I

Kriss et al. 2001

STIS & FUSE Spectra of HS1700+6416

Fechner et al. 2006

STIS Spectrum: G140L + G230LBest-fit continuum with E(B-V)=0.025

FUSE Spectrum: 290 ks

Starlight

Quasar Illumination

(NHeII/NHI) vs. Redshift (z)

Zheng et al. 2004a

Constraining Fesc for Star-forming Galaxies

Scott et al. 2001

Bianchi et al. 2001Scott et al. 2001Kriss & 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 HS1700+6416 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