The Intergalactic Medium at High Redshifts Steve Furlanetto Yale University September 25, 2007 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 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 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 Scattering Dark 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, H 2 X-rays First sources produce… Small HII regions Lyman-series photons: interact with IGM hydrogen, H 2 X-rays

The First Sources of Light: Ultraviolet Feedback H 2 Cooling Most important coolant for Pop III stars Photo-dissociated by Lyman-Werner photons ( eV) H 2 Cooling Most important coolant for Pop III stars Photo-dissociated by Lyman-Werner photons ( 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 H 2 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 H 2 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, H 2 X-rays How can we observe these backgrounds? First sources produce… Small HII regions Lyman-series photons: interact with IGM hydrogen, H 2 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 ~10 7 K: lots of heat! Dijkstra et al. (2004) Number of X-rays/H atom 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! 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)

The Spin Temperature CMB photons drive toward invisibility: T S =T CMB Collisions couple T S to T K At mean density, assuming T K and x i 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: T S =T CMB Collisions couple T S to T K At mean density, assuming T K and x i 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 0 S 1/2 1 S 1/2 0 P 1/2 1 P 1/2 1 P 3/2 2 P 3/2 Selection Rules: F=0,1 (except F=0 F=0) Mechanism is effective with ~0.1 Ly photon/baryon

The Wouthuysen-Field Mechanism II Relevant photons are continuum photons that redshift into the Ly resonance Same photons that dissociate H 2 ! Relevant photons are continuum photons that redshift into the Ly resonance Same photons that dissociate H 2 ! Ly …

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 Fluctuations Ly photons decrease T S near sources (Barkana & Loeb 2004) Clustering 1/r 2 flux Strong absorption near dense gas, weak absorption in voids Ly photons decrease T S near sources (Barkana & Loeb 2004) Clustering 1/r 2 flux Strong absorption near dense gas, weak absorption in voids Cold, Absorbing Cold, invisible

Ly Fluctuations Ly photons decrease T S near sources Clustering 1/r 2 flux Strong absorption near dense gas, weak absorption in voids Eventually saturates when IGM coupled everywhere Ly photons decrease T S near sources Clustering 1/r 2 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 T K near sources (Pritchard & Furlanetto 2007) Clustering 1/r 2 flux Hot IGM near dense gas, cool IGM near voids X-ray photons increase T K near sources (Pritchard & Furlanetto 2007) Clustering 1/r 2 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, z r =7 Thin lines: Pop III model, z r =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 galaxys metals build up? How does the transition from Pop III to Pop II occur? How do metals reach the Ly forest? How do galaxys metals build up?

Supernova 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 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 ~ kpc wind bubbles Typically Z~0.01 Zsun in these regions Expect significant absorption, e.g. CII: GP ~0.16 (Z/ Zsun) (1+z/7) 3/2 Oppenheimer & Davé (2006)

Metal Absorption Lines (1+z s ) Ly (1+z s ) metal SDSS collaboration Can probe Ly / metal < (1+z)/(1+z s ) < 1

Metal Absorption Lines Important lines: Most abundant elements produced by Type II SNe: C (Y C SN =0.1 Msun), O (0.5 Msun), Si (0.06 Msun), Fe (0.07 Msun) Most abundant elements produced by VMS SNe: C (Y C SN =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 (Y C SN =0.1 Msun), O (0.5 Msun), Si (0.06 Msun), Fe (0.07 Msun) Most abundant elements produced by VMS SNe: C (Y C SN =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 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/ 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/ 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) 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 Quasars/GRBs CMB optical depth Ly -selected galaxies Furlanetto, Oh, & Briggs (2006)

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 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 x HI ! 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 x HI ! 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? 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? 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 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 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 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) 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 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!) Similar temperature jump to observed value Requires slightly higher temperatures than expected Mean temperature lacks sudden jump (may resolve controversy!) 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 Equation of state is highly structured! Amount of structure depends on density- ionization correlation 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)

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)

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 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