gerard kriss stsci
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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
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