Observing the First Galaxies and the Reionization Epoch Steve Furlanetto UCLA February 5, 2008 Steve Furlanetto UCLA February 5, 2008

Outline Introduction: Observing Reionization Galaxy Surveys Current observations of LAEs The Clustering Signature The 21 cm Transition as a Cosmological Probe Basic Physics The Mean 21 cm Background Measurements and Challenges The Pre-reionization IGM Reionization Conclusion Introduction: Observing Reionization Galaxy Surveys Current observations of LAEs The Clustering Signature The 21 cm Transition as a Cosmological Probe Basic Physics The Mean 21 cm Background Measurements and Challenges The Pre-reionization IGM Reionization 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

Reionization First stars and galaxies produce ionizing photons Ionized bubbles grow and merge Affects all baryons in the universe Phase transition First stars and galaxies produce ionizing photons Ionized bubbles grow and merge Affects all baryons in the universe Phase transition Mesinger & Furlanetto

Reionization Mesinger & Furlanetto First stars and galaxies produce ionizing photons Ionized bubbles grow and merge Affects all baryons in the universe Phase transition First stars and galaxies produce ionizing photons Ionized bubbles grow and merge Affects all baryons in the universe Phase transition

Reionization Mesinger & Furlanetto First stars and galaxies produce ionizing photons Ionized bubbles grow and merge Affects all baryons in the universe Phase transition First stars and galaxies produce ionizing photons Ionized bubbles grow and merge Affects all baryons in the universe Phase transition

Reionization Mesinger & Furlanetto First stars and galaxies produce ionizing photons Ionized bubbles grow and merge Affects all baryons in the universe Phase transition First stars and galaxies produce ionizing photons Ionized bubbles grow and merge Affects all baryons in the universe Phase transition

Reionization: Observational Constraints Quasars/GRBs CMB optical depth Ly  -selected galaxies Quasars/GRBs CMB optical depth Ly  -selected galaxies Furlanetto, Oh, & Briggs (2006)

Ly  Emitters and HII Regions Total optical depth in Ly  transition: Damping wings are strong Total optical depth in Ly  transition: Damping wings are strong IGM HI

LAEs During Reionization z=9, R=125 observation, with M>1.7x10 10 Msun Galaxies in small bubbles (underdense regions) masked out by absorption x H =0x H =0.26x H =0.51x H =0.77 Mesinger & Furlanetto (2007)

A Declining Number Density? Largest survey to date with Subaru Apparent decline at bright end Disputed by Dawson et al. (2007) Largest survey to date with Subaru Apparent decline at bright end Disputed by Dawson et al. (2007) Kashikawa et al. (2006)

A Declining Number Density? Similar behavior to z=7 One (!) detection L>10 43 erg/s detection threshold Similar behavior to z=7 One (!) detection L>10 43 erg/s detection threshold Iye et al. (2006)

An Increasing Number Density? Stark et al. (2007) found 6 candidate LAEs behind massive clusters Search along lensing caustics z=9-10 L~ erg/s Most obvious interlopers ruled out Stark et al. (2007) found 6 candidate LAEs behind massive clusters Search along lensing caustics z=9-10 L~ erg/s Most obvious interlopers ruled out Kashikawa et al. (2006) Stark et al. (2007), z=9

An Increasing Number Density? Solid curves show mass functions with absorption Four scenarios for luminosities (right to left): Same as z=6 LAEs Same as z=6 LAEs, but Pop III All baryons form Pop II stars, simultaneously All baryons form Pop III stars, simultaneously Reasonable scenarios require fully ionized! Mesinger & Furlanetto (2008)

LAE Clustering During Reionization Nearly randomly distributed galaxy population Small bubble: too much extinction, disappears Large bubble: galaxies visible to survey Nearly randomly distributed galaxy population Small bubble: too much extinction, disappears Large bubble: galaxies visible to survey

LAE Clustering During Reionization Small bubble: too much extinction, disappears Large bubble: galaxies visible to survey Absorption selects large bubbles, which tend to surround clumps of galaxies Small bubble: too much extinction, disappears Large bubble: galaxies visible to survey Absorption selects large bubbles, which tend to surround clumps of galaxies

LAE Clustering During Reionization Small bubble: too much extinction, disappears Large bubble: galaxies visible to survey Absorption selects large bubbles, which tend to surround clumps of galaxies Small bubble: too much extinction, disappears Large bubble: galaxies visible to survey Absorption selects large bubbles, which tend to surround clumps of galaxies

Enhanced Clustering During Reionization Shows enhanced probability to have N>1 galaxies in an occupied cell Measuring requires deep survey over ~ Mpc 3 Mesinger & Furlanetto (2008)

The Future of LAE Surveys Advantages: Familiar strategies Study galaxies as well Advantages: Familiar strategies Study galaxies as well Disadvantages: Uncertainties about galaxy formation Need large volume, deep surveys Indirect information about IGM

The Spin-Flip Transition Proton and electron both have spin  magnetic fields Produces 21 cm radiation ( =1420 MHz) Extremely weak transition Mean lifetime ~10 7 yr Optical depth ~1% in fully neutral IGM Proton and electron both have spin  magnetic fields Produces 21 cm radiation ( =1420 MHz) Extremely weak transition Mean lifetime ~10 7 yr Optical depth ~1% in fully neutral IGM

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 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 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 Global Signal: The Dark Ages Straightforward physics Expanding gas Recombination Compton scattering SF, PO, FB (2006)

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 Ly  … Ly  Ly  Ly 

The Global Signal: First Light First stars (quasars?) flood Universe with photons W-F effect Trigger absorption in cold IGM First stars (quasars?) flood Universe with photons W-F effect Trigger absorption in cold IGM Pop II Stars SF (2006) feedback Pop III Stars

The First Sources of Light: X-ray Heating X-rays are highly penetrating in IGM Mean free path >Mpc Deposit energy as heat, ionization 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 Produced by… Supernovae Stellar mass black holes Quasars Very massive stars

The Global Signal: First Light First stars (quasars?) flood Universe with photons W-F effect Heating Ionization Timing depends on f *, f esc, f X, stellar population First stars (quasars?) flood Universe with photons W-F effect Heating Ionization Timing depends on f *, f esc, f X, stellar population Pop II Stars SF (2006) feedback Pop III Stars

21 cm Observations Experiments Global Signal: CoRE- ATNF, EDGES Fluctuations: 21CMA, LOFAR, MWA, GMRT, PAPER, SKA Imaging: SKA Experiments Global Signal: CoRE- ATNF, EDGES Fluctuations: 21CMA, LOFAR, MWA, GMRT, PAPER, SKA Imaging: SKA MWA

Terrestrial Interference Mileura spectrum, 15 sec integrations Two types: Fixed site (low frequency filling factor) Aircraft/meteor trail reflections (low duty cycle) Basic strategy: excise contaminated channels Bowman et al. (2007)

Ionospheric Distortions Refraction in ionosphere distorts wavefronts Analog of optical seeing layer Solved on software level with calibration sources Challenge: wide-field imaging Refraction in ionosphere distorts wavefronts Analog of optical seeing layer Solved on software level with calibration sources Challenge: wide-field imaging W. Cotton

Astronomical Foregrounds Landecker et al. (1969)  Map at 150 MHz  Contours are in Kelvin

The Synchrotron Foregrounds A single synchrotron electron produces a broad but smooth spectrum Frequency Intensity B e - path

The Synchrotron Foregrounds A single synchrotron electron produces a broad but smooth spectrum Electron velocity scales the spectrum A single synchrotron electron produces a broad but smooth spectrum Electron velocity scales the spectrum Frequency Intensity

The Synchrotron Foregrounds Synchrotron spectrum mirrors distribution of fast electrons Typically near power- law, with ~K/MHz gradient Synchrotron spectrum mirrors distribution of fast electrons Typically near power- law, with ~K/MHz gradient Frequency Intensity

Measuring the Global Signal? Signal gradient is few mK/MHz Foregrounds vary as (near) power law Synchrotron, free-free Gradient is few K/MHz CoRE-ATNF, EDGES experiments are trying Distinctive shape may help SF (2006)

Foregrounds on Small Scales 0.5 MHz

Foreground Removal Removal algorithms fairly well-developed Zaldarriaga et al. (2004), Morales & Hewitt (2004), Santos et al. (2005), McQuinn et al. (2007) Frequency TbTb Cleaned Signal ~ 10 mK Total Signal ~ 400 K

Foreground Noise Thermal noise is NOT smooth: varies between each channel For first generation instruments, 1000 hr observations still have S/N<1 per pixel Imaging is not possible until SKA! Thermal noise is NOT smooth: varies between each channel For first generation instruments, 1000 hr observations still have S/N<1 per pixel Imaging is not possible until SKA!

The Murchison Widefield Array Low Frequency Demonstrator under construction (fully funded, first light ~2008) Located on sheep ranch in Western Australia Bowman et al. (2007)

The Murchison Widefield Array Bowtie antennae grouped in tiles of 16 Broad frequency response Large field of view Bowman et al. (2007)

Murchison Widefield Array: Low Frequency Demonstrator Instrument characteristics Radio-quiet site element antennae in 1.5 km distribution 7000 m 2 total collecting area Full cross-correlation of all 500 antennae MHz 32 MHz instantaneous bandwidth at 8 kHz resolution degree field of view Instrument characteristics Radio-quiet site element antennae in 1.5 km distribution 7000 m 2 total collecting area Full cross-correlation of all 500 antennae MHz 32 MHz instantaneous bandwidth at 8 kHz resolution degree field of view Bowman et al. (2007)

Error Estimates: z=8 Survey parameters z=8 T sys =440 K t int =1000 hr B=6 MHz No systematics! MWA (solid black) A eff =7000 m km core SKA (dotted blue) A eff =1 km 2 5 km core LOFAR very close to MWA MWA SKA Foreground limit (Mpc -1 )

Error Estimates: z=12 Survey parameters z=12 T sys =1000 K t int =1000 hr B=6 MHz No systematics! MWA (solid black) A eff =9000 m km core SKA (dotted blue) A eff =1 km 2 5 km core MWA SKA Foreground limit (Mpc -1 )

That’s a whole lotta trouble… So what good is it, really? That’s a whole lotta trouble… So what good is it, really?

The Global Signal Four Phases Dark Ages First Stars First Black Holes Reionization Four Phases Dark Ages First Stars First Black Holes Reionization SF (2006) ReionizationBHsStarsDark Ages

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

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)

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

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)

X-ray Fluctuations + = Hot, emitting Cold, absorbing

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)

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)

21 cm Observations: Reionization Mesinger & Furlanetto 100 Mpc comoving

Reionization “Simulations” Implement in numerical simulation boxes Step 1: Generate initial conditions Step 2: Identify galaxies Implement in numerical simulation boxes Step 1: Generate initial conditions Step 2: Identify galaxies Mesinger & Furlanetto 100 Mpc comoving

Biased Galaxy Formation: Peaks and Patches Galaxies form at peaks in the density field Threshold decreases with time More galaxies Bigger galaxies

Identifying Galaxies Filter density field to find peaks Use excursion-set barrier to find masses Adjust locations using Zeldovich approximation Similar to “peak-patch” method (Bond & Myers 1996), PINOCCHIO, PTHALOS Mesinger & Furlanetto (2007)

Identifying Galaxies Excellent statistical agreement Large-scale structure Poisson noise Accurate one-to-one for large galaxies (Bond & Myers 1996) Mesinger & Furlanetto (2007)

Reionization “Simulations” Implement in numerical simulation boxes Step 1: Generate initial conditions Step 2: Identify galaxies Implement in numerical simulation boxes Step 1: Generate initial conditions Step 2: Identify galaxies Mesinger & Furlanetto 100 Mpc comoving

Photon Counting Assume galaxies have fixed ionizing efficiency Isolated galaxies generate HII regions Clustered galaxies work together Assume galaxies have fixed ionizing efficiency Isolated galaxies generate HII regions Clustered galaxies work together Neutral IGM Ionized IGM Galaxy

Photon Counting Assume galaxies have fixed ionizing efficiency Isolated galaxies generate HII regions Clustered galaxies work together Assume galaxies have fixed ionizing efficiency Isolated galaxies generate HII regions Clustered galaxies work together

Reionization “Simulations” Mesinger & Furlanetto z=9.75, x i = Mpc comoving Implement in numerical simulation boxes Step 1: Generate initial conditions Step 2: Identify galaxies Step 3: Paint on bubbles, working from outside in Implement in numerical simulation boxes Step 1: Generate initial conditions Step 2: Identify galaxies Step 3: Paint on bubbles, working from outside in

Reionization “Simulations” Mesinger & Furlanetto z=8.75, x i = Mpc comoving Implement in numerical simulation boxes Step 1: Generate initial conditions Step 2: Identify galaxies Step 3: Paint on bubbles, working from outside in Implement in numerical simulation boxes Step 1: Generate initial conditions Step 2: Identify galaxies Step 3: Paint on bubbles, working from outside in

Reionization “Simulations” Implement in numerical simulation boxes Step 1: Generate initial conditions Step 2: Identify galaxies Step 3: Paint on bubbles, working from outside in Implement in numerical simulation boxes Step 1: Generate initial conditions Step 2: Identify galaxies Step 3: Paint on bubbles, working from outside in Mesinger & Furlanetto z=8, x i = Mpc comoving

Reionization “Simulations” Implement in numerical simulation boxes Step 1: Generate initial conditions Step 2: Identify galaxies Step 3: Paint on bubbles, working from outside in Five hours on desktop! Implement in numerical simulation boxes Step 1: Generate initial conditions Step 2: Identify galaxies Step 3: Paint on bubbles, working from outside in Five hours on desktop! Mesinger & Furlanetto z=7.25, x i = Mpc comoving

Zahn et al. (2007), Mesinger & Furlanetto (2007) Success! Excellent match for large scale features Map details depend on filtering algorithm Filter A on halos from N-body simulation Filter B on halos from N-body simulation Radiative Transfer Simulation

The 21 cm Power Spectrum MWA SKA (Mpc -1 ) Mesinger & Furlanetto (2007) MWA SKA

21 cm-Galaxy Cross-Correlation Mesinger & Furlanetto z=8, x i =0.6

21 cm-Galaxy Cross-Correlation Key advantages Unambiguous confirmation of cosmological signal Vastly reduces difficulty of foreground cleaning Only emission from sources in survey slice contributes Increase sensitivity and dynamic range Helps with angular structure Science! Key advantages Unambiguous confirmation of cosmological signal Vastly reduces difficulty of foreground cleaning Only emission from sources in survey slice contributes Increase sensitivity and dynamic range Helps with angular structure Science!

The 21 cm-Galaxy Cross-Correlation Can be done with LAEs or LBGs Significant advantages in 21 cm data analysis (SF & AL 2007) Challenge: wide-field near-IR surveys JWST? JDEM? Ground-based cameras? Lidz, Zahn, & Furlanetto (in prep)

Conclusions LAE searches beginning to pay off Strange star formation? Robust signatures will be in clustering The 21 cm transition offers great possibilities Pre-reionization: properties of first sources, cosmology Reionization: morphology and growth of bubbles Experimental challenges still large Good synergy with other probes of high-z universe! Cross-correlation, Ly  searches, quasars… LAE searches beginning to pay off Strange star formation? Robust signatures will be in clustering The 21 cm transition offers great possibilities Pre-reionization: properties of first sources, cosmology Reionization: morphology and growth of bubbles Experimental challenges still large Good synergy with other probes of high-z universe! Cross-correlation, Ly  searches, quasars… See our Physics Reports review (Furlanetto, Oh, & Briggs 2006, astro-ph/ ) for more information on 21 cm possibilities!