the intergalactic medium at high redshifts

The Intergalactic Medium at High Redshifts

The Intergalactic Medium at High Redshifts

Steve Furlanetto

Yale University

September 25, 2007

Steve Furlanetto

Yale University

September 25, 2007

OutlineOutline

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

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 UniverseA 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: ?

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

Part I: Radiative Feedback on the IGM

The First Sources of LightThe First Sources of Light

First sources produce… Small HII regions Lyman-series photons:

interact with IGM hydrogen, H2

X-rays



X-rays

The First Sources of Light: Ultraviolet Feedback

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)

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

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

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 LightThe First Sources of Light



X-rays How can we observe

these backgrounds?



X-rays How can we observe

these backgrounds?

The X-Ray BackgroundThe 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!

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)

Nu

mb

e r o

f X

-ra y

s/H

ato

m

Miniquasars?

Mean QSO spectrum

The 21 cm TransitionThe 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!

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+ z

10

⎛

⎝ ⎜

⎞

⎠ ⎟

1/ 2 TS −TbkgdTS

⎛

⎝ ⎜

⎞

⎠ ⎟H(z) /(1+ z)

∂vr /∂r

⎛

⎝ ⎜

⎞

⎠ ⎟ mK

€

δTb ≈ 23xHI (1+ δ) 1+ z

10

⎛

⎝ ⎜

⎞

⎠ ⎟

1/ 2 TS −TbkgdTS

⎛

⎝ ⎜

⎞

⎠ ⎟H(z) /(1+ z)

∂vr /∂r

⎛

⎝ ⎜

⎞

⎠ ⎟ mK

The Spin TemperatureThe 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)

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

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

The Wouthuysen-FieldMechanism II

Relevant photons are continuum photons that redshift into the Ly resonance

Same photons that dissociate H2!

Relevant photons are continuum photons that redshift into the Ly resonance

Same photons that dissociate H2!

Ly

…

LyδLyLy

The Global Signal:First Light

The Global Signal:First Light

First stars flood Universe with soft-UV photons W-F effect Photodissociation

X-rays follow later Heating Low ionization

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 FluctuationsLy Fluctuations

Ly photons decrease TS near sources (Barkana & Loeb 2004) Clustering 1/r2 flux

Strong absorption near dense gas, weak absorption in voids

Ly photons decrease TS near sources (Barkana & Loeb 2004) Clustering 1/r2 flux


Cold, Absorbing

Cold, invisible

Ly FluctuationsLy Fluctuations

Ly photons decrease TS near sources Clustering 1/r2 flux


Eventually saturates when IGM coupled everywhere

Ly photons decrease TS near sources Clustering 1/r2 flux


Eventually saturates when IGM coupled everywhere

Cold, Absorbing

X-ray FluctuationsX-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

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 FluctuationsX-ray and Ly Fluctuations

+ =Hot,

emitting

Invisible


+ =Hot,

emitting

Cold, absorbing


+ =

Hot, emitting

The Pre-Reionization EraThe 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

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 EnrichmentPart II: Metal Enrichment

Metal EnrichmentMetal 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?

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 WindsSupernova Winds

Small galaxies have small potential wells Supernova winds

easily escape into IGM Parameterized as

“filling factor” of IGM

Small galaxies have small potential wells Supernova winds

easily escape into IGM Parameterized as

“filling factor” of IGM

Wind CharacteristicsWind 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

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 SimulationsMetal 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

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 LinesMetal Absorption Lines

(1+zs)Ly (1+zs)metal

SDSS collaboration

Can probe Ly/metal< (1+z)/(1+zs) < 1

Metal Absorption LinesMetal 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

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?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

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 ReionizationMetal 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

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”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

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

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)

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

Part III: Reionization and the IGM

Some Unsolved IGM Questions in Reionization…


What is the Ly forest actually telling us? What is the Ly forest actually telling us?

Reionization:Observational Constraints

Reionization:Observational Constraints

Quasars/GRBs CMB optical depth Ly-selected galaxies

Quasars/GRBs CMB optical depth Ly-selected galaxies

Furlanetto, Oh, & Briggs (2006)

Lyman-series Optical DepthsLyman-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

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)



What is the Ly forest actually telling us? Need precise model of the IGM

What role does photoheating play?


What role does photoheating play?

Photoheating FeedbackPhotoheating Feedback

Effectiveness is controversial (Dijkstra et al. 2004)

“Bias” of photoheating has similar effects to those for metal enrichment

Effectiveness is controversial (Dijkstra et al. 2004)

“Bias” of photoheating has similar effects to those for metal enrichment




What role does photoheating play? Need to observe the process in detail

What role do IGM recombinations play?



What role do IGM recombinations play?

Recombinations and Reionization

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

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





What role do IGM recombinations play? Need good models for interaction of sources

and IGM structures



What role do IGM recombinations play? Need good models for interaction of sources

and IGM structures

Helium ReionizationHelium 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

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 ReionizationModeling 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

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

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)

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

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!)

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

Models for Helium Reionization: Equation of State Equation of state is

highly structured! Amount of structure

depends on density-ionization correlation

Equation of state is highly structured! Amount of structure

depends on density-ionization correlation


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)

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)



Top panel: without helium reionization

Bottom panel: with helium reionization

Similar magnitude to observed value, but much different shape

Top panel: without helium reionization

Bottom panel: with helium reionization

Similar magnitude to observed value, but much different shape


ConclusionsConclusions

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

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

the intergalactic medium at high redshifts

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