1 / 84

Introduction: What is Cosmic Reionization?

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

elani
Download Presentation

Introduction: What is Cosmic Reionization?

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. 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

  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 f(HI) ~ 0 Neutral f(HI) ~ 1 Reionized f(HI) ~ 1e-5

  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. Some basics Age of the Universe IGM recombination time z > 8: trecomb < tuniv At z>6: tuniv~ 0.55 [(1+z)/10]-3/2Gyr 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

  9. Reionization: the movie Gnedin 03 8Mpc comoving

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

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

  12. 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 But…

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

  14. Reionization and the CMB • Thomson scatting during reionization (z~10) • Acoustics peaks are ‘fuzzed-out’ during reionization. • Problem: degenerate with intrinsic amplitude of the anisotropies.

  15. 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 Hinshaw et al 2008 e = 0.084 +/- 0.016 ~ L/mfp ~Lnee(1+z)2

  16. 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

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

  18. 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.)

  19. 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

  20. Constrain III: Cosmic Stromgren Sphere • Accurate zhostfrom 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: Rphys = 4.7 Mpc

  21. ‘time bounded’ Stromgren sphere: R = 4.7 Mpc # ionizing photons = # atoms in volume Luv • tqso = 4/3R3 • <nHI> => tqso = 1e5 R3 f(HI)~ 1e7yrs or f(HI) ~ 1 (tqso/1e7 yr) Loeb & Rybicki 2000

  22. Wyithe et al. 2005 CSS: Constraints on neutral fraction at z~6 P(>xHI) 90% probability x(HI) > curve = tqso/4e7 yrs • 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: f(HI) > 0.05

  23. 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

  24. 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

  25. 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

  26. 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

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

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

  29. Brightness Temperature • Brightness temp = measure of surface brightness (Jy/SR, Jy/beam, Jy/arcsec2) • TB = temp of equivalent black body, B, with surface brightness = source surface brightness at : I = S /  = B= kTB/ 2 • TB = 2 S / 2 k  • TB = physical temperature for optically thick thermal object • TA <= TB always Source size > beam TA = TB (2nd law therm.) Source size < beam TA < TB source TB [Explains the fact that temperature in focal plane of optical telescope cannot exceed TB of a source] beam telescope

  30. HI 21cm radiative transfer: large scale structure of the IGM LSS: Neutral fraction / Cosmic density / Temperature: Spin, CMB Furlanetto et al. 2006

  31. Spin Temperature Collisions w. e- and atoms Ambient photons (predominantly CMB) Ly resonant scattering: Wouthuysen-Field effect = mixing of 1S HF levels through resonant scattering of Ly drives Ts to Tkin Ly 21cm h21/k = 0.067K Each Ly photon scatters ~ 1e5 times in IGM before redshifting out of freq window.

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

  33. 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

  34. 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

  35. 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

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

  37. PS dependence on neutral fraction z=10 ‘knee’ ~ characteristic bubble scale ~ 1 to 10Mpc (cm) xi=0.78 xi = 0.13 Furlanetto et al. 2006

  38. Inside-out vs. Outside-in z=12z=15 Inside-out Outside-in Furlanetto et al. 2004

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

  40. 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

  41. 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

  42. 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

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

  44. 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

  45. Dark age HI 21cm signal: baryon oscillations 0.1 1.0 10 Mpc-1 Barkana & Loeb: “Richest of all cosmological data sets” • Three dimensional in linear regime • Probe to k ~ 103 Mpc-1 vs. CMB limit set by photon diffusion ~ 0.2Mpc-1 • Alcock-Pascinsky effect • Kaiser effect + peculiar velocites

  46. Challenge: sensitivity at very low frequency PS detection • 1 SKA, 1 yr, 30MHz (z=50), 0.1MHz • TBsky = 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

  47. BREAK

  48. Challenge I: Low frequency foreground – hot, confused sky Eberg 408 MHz Image (Haslam + 1982) Signal < 20mK Sky > 200 K DNR > 1e4 • Coldest regions: T ~ 100 (/200 z)-2.6 K • 90% = Galactic foreground • 10% = Egal. radio sources ~ 1 source deg-2 with S140 > 1 Jy

  49. 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?

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

More Related