the intergalactic medium at high redshifts
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The Intergalactic Medium at High Redshifts. Steve Furlanetto Yale University September 25, 2007. Outline. Radiative Feedback on the IGM Before Reionization Physics: first stars, first quasars Metal Enrichment Physics: winds/outflows Reionization and the IGM - PowerPoint PPT PresentationTRANSCRIPT
The Intergalactic Medium at High Redshifts
Steve FurlanettoYale University
September 25, 2007
Outline
Radiative Feedback on the IGM Before Reionization Physics: first stars, first quasars
Metal Enrichment Physics: winds/outflows
Reionization and the IGM Physics: photoheating, recombinations, IGM
structure Conclusion
A Brief History of the Universe
Last scattering: z=1089, t=379,000 yr
Today: z=0, t=13.7 Gyr
Reionization: z=6-20, t=0.2-1 Gyr
First galaxies: ?
Big Bang
Last ScatteringDark Ages
Galaxies, Clusters, etc.
Reionization
G. Djorgovski
First Galaxies
Very High Redshift
High Redshift
Low Redshift
Part I: Radiative Feedback on the IGM
The First Sources of Light
First sources produce… Small HII regions Lyman-series photons:
interact with IGM hydrogen, H2
X-rays
The First Sources of Light: Ultraviolet Feedback
H2 Cooling Most important coolant
for Pop III stars Photo-dissociated by
Lyman-Werner photons (11.26-13.6 eV)
The First Sources of Light:X-ray Heating
X-rays are highly penetrating in IGM Mean free path >Mpc Deposit energy as heat,
ionization Free electrons catalyze H2
formation! Produced by…
Supernovae Stellar mass black holes Quasars Very massive stars
The First Sources of Light
First sources produce… Small HII regions Lyman-series photons:
interact with IGM hydrogen, H2
X-rays How can we observe
these backgrounds?
The X-Ray Background
Hard X-rays can redshift to present day
Limited by unresolved soft X-ray background to ~10 X-rays/H atom
1 keV/X-ray ~107 K: lots of heat!
Dijkstra et al. (2004)
Num
b er o
f X-r
a ys /
H a
tom
Miniquasars?
Mean QSO spectrum
The 21 cm Transition
Map emission (or absorption) from IGM gas Requires no background
sources Spectral line: measure
entire history Direct measurement of
IGM properties No saturation!
SF, AS, LH (2004)
€
δTb ≈ 23xHI (1+ δ) 1+ z10
⎛ ⎝ ⎜
⎞ ⎠ ⎟
1/ 2 TS −TbkgdTS
⎛ ⎝ ⎜
⎞ ⎠ ⎟H(z) /(1+ z)∂vr /∂r
⎛ ⎝ ⎜
⎞ ⎠ ⎟ mK
The Spin Temperature
CMB photons drive toward invisibility: TS=TCMB
Collisions couple TS to TK At mean density, assuming TK and xi from
recombination, efficient until z~50 Dominated by electron exchange in H-H collisions in
neutral medium (Zygelman 2005) Dominated by H-e- collisions in partially ionized
medium (Furlanetto & Furlanetto 2006), with some contribution from H-p collisions (Furlanetto & Furlanetto 2007)
The Wouthuysen-Field Mechanism I
0S1/2
1S1/2
0P1/2
1P1/2
1P3/2
2P3/2
Selection Rules: F=0,1 (except F=0 F=0)
Mechanism is effective with ~0.1 Ly photon/baryon
The Wouthuysen-FieldMechanism II
Relevant photons are continuum photons that redshift into the Ly resonance
Same photons that dissociate H2!
Ly
…
LyδLyLy
The Global Signal:First Light
First stars flood Universe with soft-UV photons W-F effect Photodissociation
X-rays follow later Heating Low ionization Pop II Stars
SF (2006)
Pop III Stars
Ly Fluctuations
Ly photons decrease TS near sources (Barkana & Loeb 2004) Clustering 1/r2 flux
Strong absorption near dense gas, weak absorption in voids
Cold, Absorbing
Cold, invisible
Ly Fluctuations
Ly photons decrease TS near sources Clustering 1/r2 flux
Strong absorption near dense gas, weak absorption in voids
Eventually saturates when IGM coupled everywhere
Cold, Absorbing
X-ray Fluctuations
X-ray photons increase TK near sources (Pritchard & Furlanetto 2007) Clustering 1/r2 flux
Hot IGM near dense gas, cool IGM near voids
Hot
Cool
X-ray and Ly Fluctuations
+ =Hot,
emitting
Invisible
X-ray Fluctuations
+ =Hot,
emitting
Cold, absorbing
X-ray Fluctuations
+ =
Hot, emitting
The Pre-Reionization Era
Thick lines: Pop II model, zr=7
Thin lines: Pop III model, zr=7
Dashed: Ly fluctuations
Dotted: Heating fluctuations
Solid: Net signal
Ly
X-ray
Net
Pritchard & Furlanetto (2007)
Part II: Metal Enrichment
Metal Enrichment
How does the transition from Pop III to Pop II occur?
How do metals reach the Ly forest? How do galaxy’s metals build up?
Supernova Winds
Small galaxies have small potential wells Supernova winds
easily escape into IGM Parameterized as
“filling factor” of IGM
Wind Characteristics
Simple analytic model Mechanical Luminosity
provided by SN rate (and hence SFR)
Use thin-shell approximation (Tegmark et al. 1993) All mass confined to spherical
thin shell (no fragmentation) Sweeps up all IGM mass Driving force is hot bubble
interior MANY uncertainties
SF, AL (2003)
Metal Enrichment in Simulations
Expect ~1-10% of IGM enriched by z=6; galaxies surrounded by ~10-100 kpc “wind bubbles”
Typically Z~0.01 Zsun in these regions Expect significant absorption, e.g. CII:
GP~0.16 (Z/10-2.5 Zsun) (1+z/7)3/2
Oppenheimer & Davé (2006)
Metal Absorption Lines
(1+zs)Ly (1+zs)metal
SDSS collaboration
Can probe Ly/metal< (1+z)/(1+zs) < 1
Metal Absorption Lines
Important lines: Most abundant elements produced by Type II SNe: C (YC
SN=0.1 Msun), O (0.5 Msun), Si (0.06 Msun), Fe (0.07 Msun)
Most abundant elements produced by VMS SNe: C (YCSN=4.1 Msun), O
(44 Msun), Si (16 Msun), Fe (6.4 Msun) Ionization states determined by radiation background and nearby galaxy
CII, OI, SiII, FeII for neutral medium CIV, SiIV for ionized medium
Identifying lines may be difficult Doublets straightforward (high-ionization) Low-ionization probably require several lines
What Can We Learn?
z=8,f*=0.1, Q~0.07 Net absorption similar for low,
high-ionization states Strong absorbers surround
large, young galaxies Distribution of strong/weak
absorbers depends on filling factor, galaxy distribution
SF, AL (2003)
Metal Lines and Reionization
OI/HI in tight charge-exchange equilibrium ~0.14 (Z/10-2.5 Zsun) for
equivalent GP trough Dense regions enriched
first “forest” of (unsaturated) OI lines near reionization, if they remain neutral
Oh (2002)
The Real OI “Forest”
Becker et al. (2006) detected six OI systems at z>5 Four along one (highly-ionized) line of sight! CIV also detected (Ryan-Weber et al. 2006) Comparable total metal abundance to lower redshifts
Other Ways to Observe Metal Enrichment
Metal lines in the CMB (Basu et al. 2004, Hernandez-Monteagudo et al. 2007)
Direct observations of cooling lines “Fossil” enrichment at z<6 “Near-field cosmology” and old stars Ongoing Pop III star formation?
Inefficient micro-mixing? (Jimenez & Haiman 2007) New galaxies in voids? (Scannapieco et al. 2006,
Tornatore et al. 2007)
Part III: Reionization and the IGM
Some Unsolved IGM Questions in Reionization…
What is the Ly forest actually telling us?
Reionization:Observational Constraints
Quasars/GRBs CMB optical depth Ly-selected galaxies
Furlanetto, Oh, & Briggs (2006)
Reionization:Observational Constraints
Quasars/GRBs CMB optical depth Ly-selected galaxies
Furlanetto, Oh, & Briggs (2006)
Lyman-series Optical Depths
When integrating over large path length, must include cosmic web Transmission samples
unusually underdense voids
Requires model for density distribution!
Extremely difficult to measure xHI!
Different lines sample different densities
Oh & Furlanetto (2005)
Some Unsolved IGM Questions in Reionization…
What is the Ly forest actually telling us? Need precise model of the IGM
What role does photoheating play?
Photoheating Feedback
Effectiveness is controversial (Dijkstra et al. 2004)
“Bias” of photoheating has similar effects to those for metal enrichment
Some Unsolved IGM Questions in Reionization…
What is the Ly forest actually telling us? Need precise model of the IGM
What role does photoheating play? Need to observe the process in detail
What role do IGM recombinations play?
Recombinations and Reionization
Diffuse IGM “Clumping factor” uncertain by factor~30!
Minihalos Marginally important Difficult to observe
Lyman Limit systems Dramatically affect topology of reionization
and transition to “cosmic web” domination
Some Unsolved IGM Questions in Reionization…
What is the Ly forest actually telling us? Need precise model of the IGM
What role does photoheating play? Need to observe the process in detail
What role do IGM recombinations play? Need good models for interaction of sources
and IGM structures
Helium Reionization
HeII has ionization potential of 54 eV Ionized by quasars Recombination rate ~5.5
times faster Appears to occur at z~3
Direct evidence from quasar spectra
Wide range of indirect evidence
Heap et al. (2000)Heap et al. (2000)
Shull et al. (2004)Shull et al. (2004)
Modeling Helium Reionization
Apply models of hydrogen reionization to helium!
Key differences: Recombinations much
faster Double reionization? Sources rare and bright
(more stochasticity) Source population is known IGM properties are known
Evidence for Helium Reionization: Equation of State
Minimum observed temperature experiences jump at z~3.2 (though others disagree)
Accompanied by flattening of equation of state (see also Ricotti et al. 2000)
Schaye et Schaye et al. (2000)al. (2000)
Models for Helium Reionization: Equation of State Similar temperature
jump to observed value Requires slightly
higher temperatures than expected
Mean temperature lacks sudden jump (may resolve controversy!)
Furlanetto & Oh (in prep)Furlanetto & Oh (in prep)
Models for Helium Reionization: Equation of State Equation of state is
highly structured! Amount of structure
depends on density-ionization correlation
Furlanetto & Oh (in prep)Furlanetto & Oh (in prep)
Evidence for Helium Reionization: eff
Ly forest optical depth depends on temperature through recombination coefficient
Expect drop in eff at z~3 See also Bernardi et
al. (2003)Faucher-Giguère et al. (2007)Faucher-Giguère et al. (2007)
Evidence for Helium Reionization: eff
Top panel: without helium reionization
Bottom panel: with helium reionization
Similar magnitude to observed value, but much different shape
Furlanetto & Oh (in prep)Furlanetto & Oh (in prep)
Conclusions
Radiative Feedback on the IGM Before Reionization Physics: first galaxies, first X-ray sources Key observations: the 21 cm line, X-ray background
Metal Enrichment Physics: metallicity threshold, winds/outflows Key observations: quasar/GRB spectra, cooling lines
Reionization and the IGM Physics: photoheating, density distribution, recombinations Key observations: helium reionization (actually tells you a lot more)!
Conclusion