Cosmic reionization and the history of the neutral intergalactic medium Santa Fe Chris Carilli July 17, 2007 Introduction: What is Cosmic Reionization? Current constraints on the IGM neutral fraction with cosmic epoch Neutral Intergalactic Medium (IGM) – HI 21cm signals Low frequency telescopes and observational challenges

References Reionization and HI 21cm studies of the neutral IGM “Observational constraints on cosmic reionization,” Fan, Carilli, Keating 2006, ARAA, 44, 415 “Cosmology at low frequencies: the 21cm transition and the high redshift universe,” Furlanetto, Oh, Briggs 2006, Phys. Rep., 433, 181 Early structure formation and first light “The first sources of light and the reionization of the universe,” Barkana & Loeb 2002, Phys.Rep., 349, 125 “The reionization of the universe by the first stars and quasars,” Loeb & Barkana 2002, ARAA, 39, 19 “Observations of the high redshift universe,” Ellis 2007, Saas-Fe advanced course 36

History of Baryons in the Universe Ionized Neutral Reionized

WMAP – structure from the big bang Chris Carilli (NRAO) Berlin June 29, 2005 WMAP – structure from the big bang

Hubble Space Telescope Realm of the Galaxies

Dark Ages Epoch of Reionization Twilight Zone Last phase of cosmic evolution to be tested Bench-mark in cosmic structure formation indicating the first luminous structures

Dark Ages Epoch of Reionization Twilight Zone Epoch? Process? Sources?

Reionization: the movie Gnedin 03 8Mpc comoving

Some basics: What’s time…? At z > 8 trecombination < tuniv At z>6 tuniv < 1 Gyr Cen 2002 Stellar fusion produces 7e6eV/H atom. Reionization requires 13.6eV/H atom =>Need to process only 1e-5 of baryons through stars to reionize the universe

Constraint I: Gunn-Peterson Effect z Barkana and Loeb 2001

Gunn-Peterson Effect toward z~6 SDSS QSOs Fan et al 2006

Gunn-Peterson Optical depth z < 5.7 <3 z > 6.1 >7

Gunn-Peterson limits to f(HI) GP = 2.6e4 f(HI) (1+z)^3/2 End of reionization? f(HI) <1e-4 at z= 5.7 f(HI) >1e-3 at z= 6.3  to f(HI) conversion requires ‘clumping factor’  >>1 for f(HI)>0.001 => low f() diagnostic GP => Reionization occurs in ‘twilight zone’, opaque for obs <0.9 m

Contraint II: The CMB Temperature fluctuations due to density inhomogeneities at the surface of last scattering (z ~ 1000) Sound horizon at recombination ~ 1deg Angular power spectrum ~ variance on given angular scale ~ square of visibility function Sachs-Wolfe

Reionization and the CMB No reionization Reionization Thomson scatting during reionization (z~10) Acoustics peaks are ‘fuzzed-out’ during reionization. Problem: degenerate with intrinsic amplitude of the anisotropies.

e ~ l / mfp ~ l ne e (1+z)^2 = 0.09+/-0.03 CMB large scale polarization -- Thomson scattering during reionization Page + 06; Spergel 06 Scattering CMB local quadrapole => polarized Large scale: horizon scale at reionization ~ 10’s deg Signal is weak: TE = 10% TT (few uK) EE = 1% TT EE (l ~ 5)~ 0.3+/- 0.1 uK TT TE EE e ~ l / mfp ~ l ne e (1+z)^2 = 0.09+/-0.03

Rules-out high ionization fraction at z> 15 Constraint II: CMB large scale polarization -- Thomson scattering during reionization Rules-out high ionization fraction at z> 15 Allows for finite (~0.2) ionization to high z Most action occurs at z ~ 8 to 14, with f(HI) < 0.5 TT TE EE Page + 06; Spergel 06

e = integral measure to recombination=> allows many IGM histories Combined CMB + GP constraints on reionization e = integral measure to recombination=> allows many IGM histories Still a 3 result (now in EE vs. TE before)

Pushing into reionization: QSO 1148+52 at z=6.4 tuniv = 0.87Gyr Lbol = 1e14 Lo Black hole: ~3 x 109 Mo (Willot etal.) Gunn Peterson trough (Fan etal.)

1148+52 z=6.42: Gas detection M(H2) ~ 2e10 Mo zhost = 6.419 +/- 0.001 VLA Off channels Rms=60uJy 46.6149 GHz CO 3-2 IRAM M(H2) ~ 2e10 Mo zhost = 6.419 +/- 0.001 (note: zly = 6.37 +/- 0.04) VLA

Constrain III: Cosmic Stromgren Sphere Accurate zhost from CO: z=6.419+/0.001 Proximity effect: photons leaking from 6.32<z<6.419 White et al. 2003 z=6.32 ‘time bounded’ Stromgren sphere: R = 4.7 Mpc tqso = 1e5 R^3 f(HI)~ 1e7yrs or f(HI) ~ 1 (tqso/1e7 yr)

Loeb & Rybicki 2000

CSS: Constraints on neutral fraction at z~6 Nine z~6 QSOs with CO or MgII redshifts: <R> = 4.4 Mpc (Wyithe et al. 05; Fan et al. 06; Kurk et al. 07) GP => f(HI) > 0.001 If f(HI) ~ 0.001, then <tqso> ~ 1e4 yrs – implausibly short given QSO fiducial lifetimes (~1e7 years)? Probability arguments + size evolution suggest: f(HI) > 0.05 Wyithe et al. 2005 Fan et al 2005 P(>xHI) 90% probability x(HI) > curve =tqso/4e7 yrs

Cosmic Stromgren Surfaces (Hui & Haiman) zhost Larger CSS in Ly vs. Ly = Damping wing of Ly? Large N(HI) (> 1e20cm^-2) => f(HI) > 0.1

Difficulties for Cosmic Stromgren Spheres and Surfaces (Lidz + 07, Maselli + 07) Requires sensitive spectra in difficult near-IR band Sensitive to R: f(HI)  R^-3 Clumpy IGM => ragged edges Pre-QSO reionization due to star forming galaxies, early AGN activity

Not ‘event’ but complex process, large variance: zreion ~ 6 to 14 OI Not ‘event’ but complex process, large variance: zreion ~ 6 to 14 Good evidence for qualitative change in nature of IGM at z~6 ESO

Current probes are all fundamentally limited in diagnostic power OI Saturates, HI distribution function, pre-ionization? Abundance? 3, integral measure? Local ionization? Geometry, pre-reionization? Local ioniz.? Current probes are all fundamentally limited in diagnostic power Need more direct probe of process of reionization = HI 21cm line ESO

Sources responsible for reionization Luminous AGN: Not. Strong down-turn in luminous AGN population at z>3 (Fan + 06)

Sources responsible for reionization Star forming galaxies: maybe, but need to extrapolate to (not yet observed) dwarf galaxies (Bowens05; Yan04; Stark06)? Needed for reion.

Sources responsible for reionization: other possibilities Pop III stars z>10? Maybe: possible contribution to fluctuations in the midIR BG (Kashlinsky05) mini-QSOs -- unlikely due to soft Xray BG limits (Dijkstra04) Decaying sterile neutrinos -- unlikely (various BGs; Mapelli05)

Low frequency radio astronomy: Most direct probe of the neutral IGM during, and prior to, cosmic reionization, using the redshifted HI 21cm line: z>6 => 100 – 200 MHz Square Kilometer Array

HI mass limits => large scale structure Reionization 1e13 Mo 1e9 Mo

HI 21cm radiative transfer: large scale structure of the IGM LSS: Neutral fraction / Cosmic density / Temperature: Spin, CMB

Dark Ages HI 21cm signal Furlanetto et al. 2006 z > 200: T = TK = Ts due to collisions + Thomson scattering => No signal z ~ 30 to 200: TK decouples from T, but collisions keep Ts ~ TK => absorption signal z ~ 20 to 30: Density drops  Ts~ T => No signal Barkana & Loeb: “Richest of all cosmological data sets” Three dimensional in linear regime Probe to k ~ 10^3 /Mpc vs. CMB limit set by photon diffusion ~ 0.2/Mpc Alcock-Pascinsky effect Kaiser effect + peculiar velocites T = 2.73(1+z) TK = 0.026(1+z)^2 Furlanetto et al. 2006

Enlightenment and Cosmic Reionization -- first luminous sources TK T Enlightenment and Cosmic Reionization -- first luminous sources z ~ 15 to 20: TS couples to TK via Lya scattering, but TK < T => absorption z ~ 6 to 15: IGM is heated (Xrays, Lya, shocks), partially ionized => emission z < 6: IGM is fully ionized

Signal I: Global (‘all sky’) reionization signature Signal ~ 20mK < 1e-4 sky Feedback in Galaxy formation No Feedback Possible higher z absorption signal via Lya coupling of Ts -- TK due to first luminous objects Furlanetto, Oh, Briggs 06

Signal II: HI 21cm Tomography of IGM Zaldarriaga + 2003 9 7.6 TB(2’) = 10’s mK SKA rms(100hr) = 4mK LOFAR rms (1000hr) = 80mK

Signal III: 3D Power spectrum analysis  only LOFAR  + f(HI) SKA McQuinn + 06

Signal IV: Cosmic Web after reionization Ly alpha forest at z=3.6 ( < 10) Womble 96 N(HI) = 1e13 – 1e15 cm^-2, f(HI/HII) = 1e-5 -- 1e-6 => before reionization N(HI) =1e18 – 1e21 cm^-2 Lya ~ 1e7 21cm => neutral IGM opaque to Lya, but translucent to 21cm

Signal IV: Cosmic web before reionization: HI 21Forest 19mJy z=12 z=8 130MHz 159MHz radio G-P (=1%) 21 Forest (10%) mini-halos (10%) primordial disks (100%) Perhaps easiest to detect (use long baselines) ONLY way to study small scale structure during reionization

Radio sources beyond the EOR sifting problem (1/1400 per 20 sq.deg.) 1.4e5 at z > 6 S120 > 6mJy 2240 at z > 6

Signal V: Cosmic Stromgren spheres around z > 6 QSOs LOFAR ‘observation’: 20xf(HI)mK, 15’,1000km/s => 0.5 x f(HI) mJy Pathfinders: Set first hard limits on f(HI) at end of cosmic reionization Easily rule-out cold IGM (T_s < T_cmb): signal = 360 mK 5Mpc 0.5 mJy Wyithe et al. 2006

Signal VI: Dark Ages: Baryon Oscillations Very low frequency (<75MHz) = Long Wavelength Array Very difficult to detect Signal: 10 arcmin, 10mk => S30MHz = 0.02 mJy SKA sens in 1000hrs: = 20000K at 50MHz => rms = 0.2 mJy Need > 10 SKAs Need DNR > 1e6 z=50 z=150 Barkana & Loeb 2005

Challenge I: Low frequency foreground – hot, confused sky Eberg 408 MHz Image (Haslam + 1982) Coldest regions: T ~ 100 (/200 MHz)^-2.6 K 90% = Galactic foreground 10% = Egal. radio sources ~ 1 source/deg^2 with S140 > 1 Jy

Solution: spectral decomposition (eg. Morales, Gnedin…) Foreground = non-thermal = featureless over ~ 100’s MHz Signal = fine scale structure on scales ~ few MHz Cygnus A 10’ FoV; SKA 1000hrs Signal/Sky ~ 2e-5 500MHz 5000MHz Simply remove low order polynomial or other smooth function?

Cross correlation in frequency, or 3D power spectral analysis: different symmetries in frequency space for signal and foregrounds. Freq Foreground Signal Morales 2003

Cygnus A at WSRT 141 MHz 12deg field (de Bruyn) Frequency differencing  ‘errors’ are ‘well-behaved’ ‘CONTINUUM’ (B=0.5 MHz) ‘LINE’ CHANNEL (10 kHz) - CONT (Original) peak: 11000 Jy noise 70 mJy dynamic range ~ 150,000 : 1

30o x 30o Galactic foreground polarization ‘interaction’ with polarized beams  frequency dependent residuals! Solution: good calibration of polarization response NGP 350 MHz 6ox6o ~ 5 K pol IF Faraday-thin  40 K at 150 MHz WENSS: Schnitzeler et al A&A Jan07

Challenge II: Ionospheric phase errors – varying e- content TID 74MHz Lane 03 ‘Isoplanatic patch’ = few deg = few km Phase variation proportional to wavelength^2

Virgo A 6 hrs VLA 74 MHz Lane + 02 Ionospheric phase errors: The Movie Solution: Wide field ‘rubber screen’ phase self-calibration = ‘peeling’ Requires build-up of accurate sky source model 15’ Virgo A 6 hrs VLA 74 MHz Lane + 02

Challenge III: Interference 100 MHz z=13 200 MHz z=6 Solutions -- RFI Mitigation (Ellingson06) Digital filtering: multi-bit sampling for high dynamic range (>50dB) Beam nulling/Real-time ‘reference beam’ LOCATION!

Beam nulling -- ASTRON/Dwingeloo (van Ardenne) Factor 300 reduction in power

GMRT Digital Filter in Lag-space (Pen et al. 2007) 150 MHz

Leverage: existing telescopes, IF, correlator, operations VLA-VHF: 180 – 200 MHz Prime focus CSS search Greenhill, Blundell (SAO); Carilli, Perley (NRAO) Leverage: existing telescopes, IF, correlator, operations $110K D+D/construction (CfA) First light: Feb 16, 05 Four element interferometry: May 05 First limits: Winter 06/07

Project abandoned: Digital TV KNMD Ch 9 150W at 100km

RFI mitigation: location, location location… 100 people km^-2 1 km^-2 0.01 km^-2 (Briggs 2005)

Multiple experiments under-way: ‘pathfinders’ MWA (MIT/CfA/ANU) LOFAR (NL) 21CMA (China) SKA

Treion < 450mK at z = 6.5 to 10 (DNR ~ 2700) (expect ~ 20mK) EDGES (Bowman & Rogers MIT) All sky reionization HI experiment. Single broadband dipole experiment with (very) carefully controlled systematics + polynomial baseline subtraction (7th order) VaTech Dipole Ellingson rms = 75 mK Sky > 150 K Treion < 450mK at z = 6.5 to 10 (DNR ~ 2700) (expect ~ 20mK)

GMRT 230 MHz – HI 21cm abs toward highest z (~5.2) radio AGN S230MHz = 0.5 Jy GMRT at 230 MHz = z21cm RFI = 20 kiloJy ! 1” 8GHz Van Breugel et al. CO Klamer + M(H2) ~ 3e10 Mo

GMRT 230 MHz – HI 21cm abs toward highest z radio AGN (z~5.2) Limits: Few mJy/channel Few percent in optical depth 232MHz 30mJy 229Mhz 0.5 Jy rms(40km/s) = 3mJy rms(20km/s) = 5 mJy N(HI) ~ 2e20TS cm^-2 ?

Focus: Reionization (power spec,CSS,abs)

PAPER: Staged Engineering Approach Broad band sleeve dipole => 2x2 tile 8 dipole test array in GB (06/07) => 32 station array in WA (12/07) FPGA-based ‘pocket correlator’ from Berkeley wireless lab => custom design. BEE2: 5 FPGAs, 500 Gops/s S/W Imaging, calibration, PS analysis: Miriad/AIPS => Python + CASA, including ionospheric ‘peeling’ calibration + MFS ‘Peel the problem onion’ 100MHz 200MHz

PAPERGB -- 8 Ant, 1hr, 12/06 RMS ~ 15Jy; DNR ~ 1e3 CygA 1e4Jy Cas A 1e3Jy CygA 1e4Jy 5deg W44 1e2Jy HercA 1e2Jy

Destination: Moon! No interference (ITU protected zone) No ionosphere (?) Easy to deploy and maintain (high tolerance electronics + no moving parts) 10MHz Needed for probing ‘Dark ages’: z>30 => freq < 50 MHz RAE2 1973

Radio astronomy – Probing Cosmic Reionization ‘Twilight zone’: study of first light limited to near-IR to radio First constraints: GP, CMBpol => reionization is complex and extended: z_reion = 6 to 11 HI 21cm: most direct probe of reionization Low freq pathfinders: All-sky, PS, CSS SKA: imaging of IGM

Relative evolution of Ly-break (UV continuum) and Ly galaxy populations: Obscuration by the neutral IGM Two methods for finding very high z galaxies I. Ly emitters: narrow band search -- affected by IGM abs 850nm => z=5.7 II. Ly-break galaxies: broad band search -- not affected by IGM abs

Effect of neutral IGM on LAE vs. LBG z LAE UV continuum = LBG Barkana and Loeb 2001

Local ionization (CSS)? Low S/N Relative evolution of Ly-break and Ly galaxy populations: Obscuration by the neutral IGM (Ota + 2007) LAE observed z=5.7 LAE predicted z=7 based on UV continuum At z=7 => f(HI)=0.48+/-0.16 LAE obs z=7 Local ionization (CSS)? Low S/N

END

Inverse Compton losses off the CMB = U_B (radio lobe)

Evolution of the neutral IGM (Gnedin): ‘Cosmic Phase transition’ HI fraction Ionizing intensity density Gas Temp 6 Mpc (comoving)

Early structure formation: rules-of-thumb (Barkana & Loeb 2002) Baryons: astrophysics Dark Matter Press-Schechter Formalism M’Jeans’ = 1e4 Msun (z=20) Minihalos: H2 cooling: Tvir = 300 to 1e4 K => M = 1e5 to 1e8 Msun issues: primordial H_2 formation? Near UV dissociates H_2? Soft Xray catalyzes H_2 formation? Preferentially form 100 M_sun stars (popIII)? Protogalaxies: H line cooling => T_vir > 1e4 K z M2 Tvir Msun K 0 1e14 3e7 5 3e10 3e5 6e7 8e3

e = integral measure to recombination=> allows many IGM histories Combined CMB + GP constraints on reionization e = integral measure to recombination=> allows many IGM histories Still a 3 result (now in EE vs. TE before)

Some basics Structure formation: the Dark Matter perspective = Press-Schechter Formalism z M_2s T_vir M_sun K 0 1e14 3e7 5 3e10 3e5 10 6e7 8e3

Structure formation: the Baryons Some basics Structure formation: the Baryons Minihalos z>15: M=1e5 to 1e8Mo => Tvir = 300 to 1e4 K => H2 cooling Primordial H2 formation? Near UV dissociates H2? Soft Xray catalyzes H2 formation? Preferentially form 100 Mo stars? Protogalaxies z<15: 1e8Mo => Tvir > 1e4 K => HI line cooling [Cosmological Jeans mass < 1e4 Mo at z>20]

Current probes are all fundamentally limited in diagnostic power OI Saturates, HI distribution function, pre-ionization? Abundance? 3, integral measure? Local ionization? Geometry, pre-reionization? Local ioniz? LAE gal Current probes are all fundamentally limited in diagnostic power Need more direct probe of process of reionization = HI 21cm line ESO

SDSS QSO CSS => rapid reionization at z~7 ? ESO