Probing the neutral intergalactic medium during cosmic reionization using the 21cm line of hydrogen KIAA-PKU Summer School, Beijing, China Chris Carilli, NRAO, August 10, 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

Ionized Neutral Reionized History of Baryons in the Universe

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

Hubble Space Telescope Realm of the Galaxies

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

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

Cen 2002 Some basics 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 At z>6: t univ ~ 0.55 [(1+z)/10] -3/2 Gyr z > 8: t recomb < t univ

Gnedin 03 Reionization: the movie 8Mpc comoving

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

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

Gunn- Peterson limits to f(HI)  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  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 But…

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

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

Constraint II: CMB large scale polarization -- Thomson scattering during reionization   Scattering CMB local quadrapole => polarized   Large scale: horizon scale at reioniz ~ 10’s deg  Signal is weak: TE ~ 10% TT EE ~ 1% TT  e = / ~ L/mfp ~ Ln e  e  (1+z) 2 Hinshaw et al 2008

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 Dunkley et al. 2008

 e = integral measure to recombination=> allows many IGM histories Combined CMB + GP constraints on reionization But…

t univ = 0.87Gyr L bol = 1e14 L o Black hole: ~3 x 10 9 M o ( Willot etal. ) Gunn Peterson trough (Fan etal.) Pushing into reionization: QSO at z=6.4

z=6.42: Gas detection Off channels Rms=60uJy GHz CO 3-2 M(H 2 ) ~ 2e10 M o z host = / (note: z ly  = /- 0.04) VLA IRAM VLA

Constrain III: Cosmic Stromgren Sphere Accurate z host from CO: z= / Proximity effect: photons leaking from 6.32<z<6.419 z=6.32 ‘time bounded’ Stromgren sphere: R = 4.7 Mpc t qso = 1e5 R 3 f(HI)~ 1e7yrs or f(HI) ~ 1 (t qso /1e7 yr) White et al. 2003

Loeb & Rybicki 2000

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

CSS: Constraints on neutral fraction at z~6 Fan et al 2005

Difficulties for Cosmic Stromgren Spheres (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

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

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

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

Advantages to the HI 21cm line 1.Spectral line signal => full three dimensional (3D) diagnostic of structure formation. 2.Direct probe of IGM = dominant component of baryons during reinization/dark ages 3.Hyperfine transition = forbidden (weak) => avoid saturation (cf. Ly  ),  can study the full redshift range of reionization. Diagnostics: 1.When: direct measure of epoch of reionization 2.Process: Inside-out vs. outside-in reionization 3.Sources: Xrays vs. UV vs. shocks 4.Feedback due to galaxy/AGN formation 5.Exotic mechanisms: Very high z particle decay

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

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

Spin Temperature 1.Collisions w. e - and atoms 2.Ambient photons (predominantly CMB) 3.Ly  resonant scattering: Wouthuysen-Field effect = mixing of 1S HF levels through resonant scattering of Ly  drives T s to T kin Ly  21cm Each Ly  photon scatters ~ 1e5 times in IGM before redshifting out of freq window.

Dark Ages HI 21cm signal z > 200: T  = T K = T s due to collisions + Thomson scattering => No signal z ~ 30 to 200: T K decouples from T , but collisions keep T s ~ T K => absorption signal z ~ 20 to 30: Density drops  T s ~ T  => No signal T K = 0.026(1+z)^2 T  = 2.73(1+z) Furlanetto et al. 2006

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

Signal I: Global (‘all sky’) reionization signature Signal ~ 20mK < 1e-4 sky Possible higher z absorption signal via Lya coupling of T s -- T K due to first luminous objects Feedback in galaxy formation No Feedback Furlanetto, Oh, Briggs 06

Signal II: HI 21cm Tomography of IGM Zaldarriaga z=   T B (2’) = 10’s mK  SKA rms(100hr) = 4mK  LOFAR rms (1000hr) = 80mK

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

PS dependence on neutral fraction x i = 0.13 x i =0.78 z=10 Furlanetto et al. 2006

Inside-out vs. Outside-in Furlanetto et al z=12 z=15 Inside-out Outside-in

Sensitivity of MWA for PS measurements (Lidz et al. 2007) 1yr, 30MHz/6MHz  Will measure PS variance over k ~ 0.1 to 1 Mpc -1  Sensitivity is maximized with compact array configuration (blue)

Sensitivity of MWA for PS measurements (Lidz et al. 2007)  Constrain amplitude of PS (variance) to 5 to 10   Constrain slope of PS to similar accuracy

N(HI) = 1e13 – 1e15 cm^-2, f(HI/HII) = 1e e-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 after reionization Ly alpha forest at z=3.6 (  < 10) Womble 96

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

Radio sources beyond the EOR sifting problem (1/1400 per 20 sq.deg.) 2240 at z > 6 1.4e5 at z > 6 S 120 > 6mJy

Signal V: Cosmic Stromgren spheres around z > 6 QSOs 0.5 mJy  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 Wyithe et al Mpc

Dark age HI 21cm signal: baryon oscillations Barkana & Loeb: “Richest of all cosmological data sets” Three dimensional in linear regime Probe to k ~ 10 3 Mpc -1 vs. CMB limit set by photon diffusion ~ 0.2Mpc -1 Alcock-Pascinsky effect Kaiser effect + peculiar velocites Mpc -1

Challenge: sensitivity at very low frequency PS detection 1 SKA, 1 yr, 30MHz (z=50), 0.1MHz T Bsky = 100( /200MHz) -2.7 K = 1.7e4 K At l=3000, k=0.3 Mpc -1 Signal ~ 2 mK Noise PS ~ 1 mK  Requires few SKAs

BREAK

Challenge I: Low frequency foreground – hot, confused sky Eberg 408 MHz Image (Haslam ) Coldest regions: T ~ 100  z) -2.6 K 90% = Galactic foreground 10% = Egal. radio sources ~ 1 source deg -2 with S 140 > 1 Jy

Solution: spectral decomposition (eg. Morales, Gnedin…)  Foreground = non-thermal = featureless over ~ 100’s MHz  Signal = fine scale structure on scales ~ few MHz 10’ FoV; SKA 1000hrs Signal/Sky ~ 2e-5 Cygnus A 500MHz5000MHz 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 Signal Foreground 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: Jy noise 70 mJy dynamic range ~ 150,000 : 1

Cygnus A w. PAPER/GB 130 MHz 30deg FoV Frequency differencing doesn’t work well for far-out sidelobes due to chromatic aberration. 1MHz separation 5MHz separation 10 o

Calibration requirements for point source removal  20 o x 20 o FoV => expect brightest source ~ 34Jy at 158MHz  CSS detection: 10mK signal over 10’ = 73 uJy  required DNR = 34Jy/73uJy = 4.6e5  DNR ~ N ant / (2 1/2 x rms phase error in rad)  500 element array => required rms phase error ~ o

Galactic foreground polarization ‘interaction’ with polarized beams  frequency dependent residuals! Solution: good calibration of polarization response NGP 350 MHz 6 o x6 o ~ 5 K pol IF Faraday-thin  40 K at 150 MHz WENSS: Schnitzeler et al A&A Jan07 30 o x 30 o

 Phase variation proportional to wavelength^2 Challenge II: Ionospheric phase errors – varying e- content

 ‘Isoplanatic patch’ = few deg = few km 74MHz Lane 03 Challenge II: Ionospheric phase errors – varying e- content TID

Solution:  Direction dependent calibration: Wide field ‘rubber screen’ phase self- calibration = ‘peeling’ Virgo A 6 hrs VLA 74 MHz Lane ’ Ionospheric phase errors: The Movie

Challenge III: Interference 100 MHz z= 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

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^ km^-2 (Briggs 2005)

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

Complication: ‘Tile’ diffraction beam

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

Limits to the Global Step in the HI 21cm signal

Currently limited by systematics After ~1/2 hour, rms no longer decreases as root time

GMRT 230 MHz – HI 21cm abs toward highest z (~5.2) radio AGN z=5.2 S 230MHz = 0.5 Jy 1” 8GHz Van Breugel et al. GMRT at 230 MHz = z 21cm RFI = 20 kiloJy ! CO Klamer + M(H 2 ) ~ 3e10 M o

GMRT 230 MHz – HI 21cm abs toward highest z radio AGN (z~5.2) rms(20km/s) = 5 mJy 229Mhz 0.5 Jy 232MHz 30mJy rms(40km/s) = 3mJy N(HI) ~ 2e20T S cm -2 ? Limits:  Few mJy/channel  Few percent in optical depth

Focus: Reionization (power spec,CSS,abs)

PAPER: Staged Engineering Broad band sleeve dipole + flaps 8 dipole test array in GB (06/07) => 32 station array in WA (2008) to 256 (2009) FPGA-based ‘pocket correlator’ from Berkeley wireless lab S/W Imaging, calibration, PS analysis: AIPY + Miriad/AIPS => Python + CASA, including ionospheric ‘peeling’ calibration 100MHz200MHz BEE2: 5 FPGAs, 500 Gops/s

CygA 1e4Jy PAPER/WA -- 4 Ant, July 2007 RMS ~ 1Jy; DNR ~ 1e4 Parsons et al e4Jy

Lunatic fringe: probing the dark ages from the dark side of the Moon C. Carilli (NRAO), Sackler Cosmology Conf, Cambridge, MA, 2008

Return to moon is Presidential national security directive (an order, not a request). Summary of STScI Workshop, Mario Livio, Nov “The workshop has identified a few important astrophysical observations that can potentially be carried out from the lunar surface. The two most promising in this respect are: (i)Low-frequency radio observations from the lunar far side to probe structures in the high redshift (10 < z< 100) universe and the epoch of reionization (ii)Lunar ranging experiments…” Our consensus: Lunar imperative awaits lessons from ground- arrays

Advantage I: Interference Lunar shielding of Earth’s auroral emission at low freq (Radio Astronomy Explorer 1975) Alexander MHz ITU radio regulation Article 22: Far-side of Moon is a radio protected by international agreement

Clementine (NRL) star tracker Advantage II: Very thin ionosphere -- critical at very low frequencies  Tenuous photoionized layer extending to 100km  p = 0.2 to 1 MHz ~ 0.01 to 0.1 x Earth  large day/night variation

Other advantages Easier deployment: robotic or human Easier maintenance (no moving parts) Less demanding hardware tolerances Very large collecting area, undisturbed for long periods (no weather, no animals, not many people)

Apollo 15 Array data rates (Tb/s) >> telemetry limits, requiring in situ processing, ie. low power super computing (LOFAR/Blue Gene = 0.15MW) RFI shielding: How far around limb is required? Thermal cycling (mean): 120 K to 380 K Radiation environment Regolith: dielectric/magnetic properties Lunar challenges Lunar shielding at 60kHz Takahashi + Woan

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 = 7 to 15 HI 21cm: most direct probe of reionization Low freq pathfinders: All-sky, PS, CSS SKA: direct imaging of IGM Lunar array to probe the Dark Ages

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