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Cosmic reionization and the history of the neutral intergalactic medium

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

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Cosmic reionization and the history of the neutral intergalactic medium

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  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. History of Baryons in the Universe Ionized Neutral Reionized

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

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

  8. Reionization: the movie Gnedin 03 8Mpc comoving

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

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

  11. 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

  12. 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

  13. 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.

  14. 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

  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

  16. 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)

  17. 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.)

  18. 1148+52 z=6.42: Gas detection 46.6149 GHz CO 3-2 Off channels Rms=60uJy VLA IRAM • M(H2) ~ 2e10 Mo • zhost = 6.419 +/- 0.001 (note: zly = 6.37 +/- 0.04) VLA

  19. 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)

  20. Loeb & Rybicki 2000

  21. 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

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

  24. 3, integral measure? Geometry, pre-reionization? Local ionization? OI Abundance? Saturates, HI distribution function, pre-ionization? Local ioniz.? • Current probes are all fundamentally limited in diagnostic power • Need more direct probe of process of reionization = HI 21cm line ESO

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

  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 = 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

  29. TK T Enlightenment and Cosmic Reionization-- first luminous sources • z ~ 15 to 20: TScouples 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

  30. 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

  31. Signal II: HI 21cm Tomography of IGM Zaldarriaga + 2003 z=12 9 7.6 • TB(2’) = 10’s mK • SKA rms(100hr) = 4mK • LOFAR rms (1000hr) = 80mK

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

  33. 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

  34. 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

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

  36. 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

  37. 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

  38. 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

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

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

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

  44. 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

  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’ LOFAR (NL) MWA (MIT/CfA/ANU) SKA 21CMA (China)

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