Radiation backgrounds from the first sources and the redshifted 21 cm line

1. Radiation backgrounds from the first sources and the redshifted 21 cm line Jonathan Pritchard (Caltech) Collaborators: Steve Furlanetto (Yale) Advisor: Marc Kamionkowski (Caltech)

2. Overview • Atomic cascades and the Wouthysen-Field Effect • Detecting the first stars through 21 cm fluctuations (Lya) • Inhomogeneous X-rayheating and gas temperature fluctuations (X-ray) • Observational prospects z~30 z~12

3. Ionization history • Gunn-Peterson Trough Becker et al. 2005 • Universe ionized below z~6, some neutral HIat higher z • black is black • WMAP3 measurement oft~0.09 (down from t~0.17) Page et al. 2006 • Integral constraint on ionization history • Better TE measurements+ EE observations

4. Thermal history • Lya forest Zaldarriaga, Hui, & Tegmark 2001 Hui & Haiman 2003 ?? • IGM retains short term memory of reionization - suggests zR<10 • Photoionization heating erases memory of thermal history beforereionization • CMB temperature • Knowing TCMB=2.726 K and assuming thermal coupling byCompton scattering followed by adiabatic expansion allows informed guess of high z temperature evolution

5. TS Tb Tg HI TK 21 cm basics • Use CMB backlight to probe 21cm transition • HI hyperfine structure n1 11S1/2 l=21cm 10S1/2 n0 z=0 z=13 n1/n0=3 exp(-hn21cm/kTs) fobs=100 MHz f21cm=1.4 GHz • 3D mapping of HI possible - angles + frequency • 21 cm brightness temperature • 21 cm spin temperature Coupling mechanisms: Radiative transitions (CMB) Collisions Wouthuysen-Field

6. Wouthysen-Field effect Hyperfine structure of HI 22P1/2 21P1/2 Effective for Ja>10-21erg/s/cm2/Hz/sr Ts~Ta~Tk 21P1/2 20P1/2 W-F recoils Field 1959 nFLJ Lymana 11S1/2 Selection rules: DF= 0,1 (Not F=0F=0) 10S1/2

7. Higher Lyman series • Two possible contributions • Direct pumping: Analogy of the W-F effect • Cascade: Excited state decays through cascade to generate Lya • Direct pumping is suppressed by the possibility of conversion into lower energy photons • Ly a scatters ~106 times before redshifting through resonance • Ly n scatters ~1/Pabs~10 times before converting • Direct pumping is not significant • Cascades end through generation of Ly a or through a two photon decay • Use basic atomic physics to calculate fraction recycled into Ly a • Discuss this process in the next few slides… Pritchard & Furlanetto 2006 Hirata 2006

8. Lyman b A3p,2s=0.22108s-1 A3p,1s=1.64108s-1 gg • Optically thick to Lyman series • Regenerate direct transitions to ground state • Two photon decay from 2S state • Decoupled from Lyman a • frecycle,b=0 Agg=8.2s-1

9. Lyman g • Cascade via 3S and 3D levelsallows production of Lyman a • frecycle,g=0.26 • Higher transitions frecycle,n~ 0.3 gg

10. Lyman alpha flux • Stellar contribution continuum injected • also a contribution from X-rays…

11. X-rays and Lya production spiE-3 HI HII photoionization e- X-ray collisionalionization e- Lya excitation (fa0.8) HI Chen & Miralda-Escude 2006 Shull & van Steenberg 1985 heating

12. Experimental efforts MWA: Australia Freq: 80-300 MHz Baselines: 10m- 1.5km PAST/21CMA: China Freq: 70-200 MHz LOFAR: Netherlands Freq: 120-240 MHz Baselines: 100m- 100km SKA: S Africa/Australia Freq: 60 MHz-35 GHz Baselines: 20m- 3000km (f21cm=1.4 GHz)

13. Foregrounds • Many foregrounds • Galactic synchrotron (especially polarized component) • Radio Frequency Interference (RFI) e.g. radio, cell phones, digital radio • Radio recombination lines • Radio point sources • Foregrounds dwarf signal: foregrounds ~1000s K vs 10s mK signal • Strong frequency dependence Tskyn-2.6 • Foreground removal exploits smoothness in frequency and spatial symmetries

14. Global history Furlanetto 2006 Adiabaticexpansion X-rayheating + + Comptonheating Heating expansion UV ionization + recombination HII regions X-ray ionization + recombination IGM Lya flux continuum injected • Sources: Pop. II & Pop. III stars (UV+Lya) Starburst galaxies, SNR, mini-quasar (X-ray) • Source luminosity tracks star formation rate • Many model uncertainties

15. Ionization history zR~7t~0.07 Xi>0.1 • Models differ by factor ~10 in X-ray/Lya per ionizing photon • Reionization well underway at z<12

16. Thermal history

17. ZR ZT Za Z* Z30 Z~150 No 21 cm signal Collisionallycoupled regime Density Ly X-ray UV 21 cm fluctuations W-FCoupling Velocitygradient BaryonDensity Neutralfraction Gas Temperature Brightnesstemperature Cosmology Reionization X-raysources Lyasources Cosmology Twilight Dark Ages Reionization TS~Tg

18. Angular separation? W-FCoupling Velocitygradient BaryonDensity Neutralfraction Gas Temperature • In linear theory, peculiar velocities correlate with overdensities Bharadwaj & Ali 2004 • Anisotropy of velocity gradient term allows angular separation Barkana & Loeb 2005 • Initial observations will average over angle to improve S/N

19. ZR ZT Za Z* Z30 Z~150 No 21 cm signal Collisionallycoupled regime Density Ly X-ray UV 21 cm fluctuations W-FCoupling Velocitygradient BaryonDensity Neutralfraction Gas Temperature Brightnesstemperature Cosmology Reionization X-raysources Lyasources Cosmology Twilight Dark Ages Reionization TS~Tg

20. Reionization Neutralfraction Gas Temperature W-FCoupling Velocitygradient Density Lya coupling saturated IGM hotTK>>Tg HII regions large Z=12.1 Z=9.2 Z=8.3 Z=7.6 Furlanetto, Sokasian, Hernquist 2003

21. 21 cm fluctuations: Lya Neutralfraction Gas Temperature W-FCoupling Velocitygradient Density -negligible heating of IGM-tracks density IGM still mostlyneutral Lya flux varies • Lya fluctuations unimportant after coupling saturates (xa>>1) • Three contributions to Lya flux: • Stellar photons redshifting into Lya resonance • Stellar photons redshifting into higher Lyman resonances • X-ray photoelectron excitation of HI Chen & Miralda-Escude 2004 Chen & Miralda-Escude 2006

22. d dV Fluctuations from the first stars • Fluctuations in flux from source clustering, 1/r2 law, optical depth,… • Relate Lya fluctuations to overdensities Barkana & Loeb 2005 • W(k) is a weighted average

23. Determining the first sources da dominates source properties density bias Chuzhoy,Alvarez, & Shapiro 2006 Sources Ja,* vs Ja,X Pritchard & Furlanetto 2006 Spectra aS z=20 D=[k3P(k)/2p]1/2

24. 21cm fluctuations: TK Neutralfraction Gas Temperature W-FCoupling Velocitygradient Density couplingsaturated IGM still mostlyneutral density + x-rays • In contrast to the other coefficients bT can be negative • Sign of bT constrains IGM temperature Pritchard & Furlanetto 2006

25. Temperature fluctuations TS~TK<Tg Tb<0 (absorption)Hotter region = weaker absorption bT<0 TS~TK~Tg Tb~021cm signal dominated by temperature fluctuations TS~TK>Tg Tb>0 (emission) Hotter region = stronger emission bT>0

26. d dV X-ray heating • X-rays provide dominant heating source in early universe(shocks possibly important very early on) • X-ray heating often assumed to be uniform as X-rays have long mean free path • Simplistic, fluctuations may lead to observable 21cm signal • X-ray flux -> heating rate -> temperature Mpc adiabatic index -1 Barkana & Loeb 2005

27. Growth of fluctuations expansion X-rays Compton temperature fluctuations Heating fluctuations Fractional heating per Hubble time at z dT/ d=

28. TK fluctuations • Fluctuations in gas temperature can be substantial • Amplitude of fluctuations contains information about IGM thermal history

29. TK<Tg Angle averaged power spectrum TK>Tg m2 part of power spectrum Indications of TK dT dominates • Constrain heating transition • Dm2 <0 on largescales indicates TK<Tg(but can have Pdx<0)

30. X-ray source spectra • Sensitivity to aS through peak amplitude and shape • Also through position of trough • Effect comes from fraction of soft X-rays

31. dx dT da ? X-ray background? • X-ray background at high z is poorly constrained Extrapolating low-z X-ray:IR correlation gives: Glover & Brand 2003 • 1st Experiments might see TK fluctuations if heating late

32. 21 cm fluctuations: z ? • Exact form very model dependent

33. Redshift slices: Lya z=19-20 • Pure Lya fluctuations

34. Redshift slices: Lya/T z=17-18 • Growing T fluctuationslead first to dip inDTb then to double peak structure • Double peak requiresT and Lya fluctuationsto have different scaledependence

35. Redshift slices: T z=15-16 • T fluctuations dominate over Lya • Clear peak-trough structure visible • Dm2 <0 on largescales indicates TK<Tg

36. Redshift slices: T/d z=13-14 • After TK>Tg , thetrough disappears • As heating continuesT fluctuations die out • Xi fluctuations willstart to become important at lower z

37. Observations poor angular resolution foregrounds • Need SKA to probe these brightnessfluctuations • Observe scalesk=0.025-2 Mpc-1 • Easily distinguishtwo models • Probably won’t seetrough :(

38. Conclusions • 21 cm fluctuations potentially contain much information about the first sources • Bias • X-ray background • X-ray source spectrum • IGM temperature evolution • Star formation rate • Lya and X-ray backgrounds may be probed by future 21 cm observations • Foregrounds pose a challenging problem at high z • SKA needed to observe the fluctuations described here • Will be interesting to include spin temperature fluctuationsin future simulations For more details see astro-ph/0607234 & astro-ph/0508381

40. Extra Slides

41. TS Tb Tg n1 11S1/2 l=21cm HI 10S1/2 n0 TK 21 cm basics • HI hyperfine structure n1/n0=3 exp(-hn21cm/kTs) • Use CMB backlight to probe 21cm transition z=0 z=13.75 fobs=94.9 MHz f21cm=1.4 GHz (KUOW) • 3D mapping of HI possible - angles + frequency

42. 21 cm basics • 21 cm brightness temperature • 21 cm spin temperature

43. The first sources 1000 Mpc Hard X-rays Lya 330 Mpc Soft X-rays HII 5 Mpc 0.2 Mpc z=15

44. d dV X-ray heating • X-rays provide dominant heating source in early universe(shocks possibly important very early on) • X-ray heating often assumed to be uniform as X-rays have long mean free path • Simplistic, fluctuations may lead to observable 21cm signal • Fluctuations in JX arise in same way as Ja Mpc photo-ionization time integral

45. Growth of fluctuations expansion X-rays Compton temperature fluctuations Heating fluctuations Fractional heating per Hubble time at z