1. Cosmic reionization and the history of the neutral intergalactic medium MAGPOP Summer School, Kloster Seeon 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

2. 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

3. Ionized Neutral Reionized History of Baryons in the Universe

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

5. Hubble Space Telescope Realm of the Galaxies

6. 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

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

8. Gnedin 03 Reionization: the movie 8Mpc comoving

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

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

11. 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

12. 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

13. 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

14. TT TE EE CMB large scale polarization -- Thomson scattering during reionization   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 Page + 06; Spergel 06  e ~ l / mfp ~ l n e  e  (1+z)^2 = 0.09+/-0.03

15. TT TE EE 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 Page + 06; Spergel 06

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

17. 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 1148+52 at z=6.4

18. 1148+52 z=6.42: Gas detection Off channels Rms=60uJy 46.6149 GHz CO 3-2 M(H 2 ) ~ 2e10 M o z host = 6.419 +/- 0.001 (note: z ly  = 6.37 +/- 0.04) VLA IRAM VLA

19. Constrain III: Cosmic Stromgren Sphere Accurate z host from CO: z=6.419+/0.001 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

20. Loeb & Rybicki 2000

21. 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) > 0.001  If f(HI) ~ 0.001, then ~ 1e4 yrs – implausibly short given QSO fiducial lifetimes (~1e7 years)?  Probability arguments + size evolution suggest: f(HI) > 0.05 Wyithe et al. 2005 =t qso /4e7 yrs 90% probability x(HI) > curve P(>x HI ) Fan et al 2005

22. 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

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

24. ESO OI Saturates, HI distribution function, pre-ionization? Abundance? 3 , 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.?

25. 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

26. 1e13 M o 1e9 M o HI mass limits => large scale structure Reionization

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

28. 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 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 K = 0.026(1+z)^2 T  = 2.73(1+z) Furlanetto et al. 2006

29. 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

30. 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

31. Signal II: HI 21cm Tomography of IGM Zaldarriaga + 2003 z=1297.6   T B (2’) = 10’s mK  SKA rms(100hr) = 4mK  LOFAR rms (1000hr) = 80mK

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

33. 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 after reionization Ly alpha forest at z=3.6 (  < 10) Womble 96

34. 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

35. 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

36. 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. 2006 5Mpc

37. Signal VI: Dark Ages: Baryon Oscillations Very low frequency (<75MHz) = Long Wavelength Array Very difficult to detect  Signal: 10 arcmin, 10mk => S 30MHz = 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

38. Challenge I: Low frequency foreground – hot, confused sky Eberg 408 MHz Image (Haslam + 1982) Coldest regions: T ~ 100  z)^-2.6 K 90% = Galactic foreground 10% = Egal. radio sources ~ 1 source/deg^2 with S 140 > 1 Jy

39. 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?

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

41. 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

42. 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

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

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

45. 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!

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

47. 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

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

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

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

53. 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

54. GMRT 230 MHz – HI 21cm abs toward highest z (~5.2) radio AGN 0924-220 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

55. 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

56. Focus: Reionization (power spec,CSS,abs)

57. 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’ 100MHz200MHz

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

59. Destination: Moon! RAE2 1973  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

60. 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

61. END

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

63. Dark Matter Press-Schechter Formalism z M 2  T vir Msun K 0 1e14 3e7 5 3e10 3e5 10 6e7 8e3 M ’Jeans’ = 1e4 M sun (z=20) Minihalos: H 2 cooling: T vir = 300 to 1e4 K => M = 1e5 to 1e8 M sun 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 Baryons: astrophysics Early structure formation: rules-of-thumb (Barkana & Loeb 2002)

64. Some basics Structure formation: the Dark Matter perspective = Press-Schechter Formalism z M_ 2  T _vir M_sun K 0 1e14 3e7 5 3e10 3e5 10 6e7 8e3

65. Minihalos z>15: M=1e5 to 1e8M o => T vir = 300 to 1e4 K => H 2 cooling Primordial H 2 formation? Near UV dissociates H 2 ? Soft Xray catalyzes H 2 formation? Preferentially form 100 M o stars? Protogalaxies z T vir > 1e4 K => HI line cooling [Cosmological Jeans mass 20] Some basics Structure formation: the Baryons

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

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

68. Cen 2002 Some basics: What’s time…? 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 < 1 Gyr At z > 8 t recombination < t univ