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) Marc Kamionkowski (Caltech) Work based on astro-ph/0607234 astro-ph/0508381

2. Overview • 21 cm physics • 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)

3. Ionization history • Gunn-Peterson Trough Becker et al. 2005 • Universe ionized below z~6, approaching neutral at higher z • 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 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=13.75 n1/n0=3 exp(-hn21cm/kTs) fobs=94.9 MHz f21cm=1.4 GHz (KUOW) • 3D tomography possible - angles + frequency • 21 cm brightness temperature • 21 cm spin temperature

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 any 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: China Freq: 70-200 MHz LOFAR: Netherlands Freq: 120-240 MHz Baselines: 100m- 100km SKA: ??? 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. The first sources 1000 Mpc Hard X-rays Lya 330 Mpc Soft X-rays HII 5 Mpc 0.2 Mpc z=15

15. Cosmological context ZR ZT Za Z* Z30 CMB Lya X-ray UV • Three main regimes for 21 cm signal • Each probes different radiation field

16. 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

17. Thermal history

18. Ionization history Xi>0.1 • Ionization fluctuations relevant for z<12, not so important above that redshift. • We’ll restrict to fluctuations at z>13 Furlanetto, Zaldarriaga, Hernquist 2004

19. 21 cm fluctuations W-FCoupling Velocitygradient BaryonDensity Neutralfraction Gas Temperature Radiation backgroundprobed: UV X-ray Lya • 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

20. 21 cm fluctuations: z ? • Exact form very model dependent

21. 21 cm fluctuations: Lya Neutralfraction Gas Temperature W-FCoupling Velocitygradient Density IGM still mostlyneutral negligible heating of IGM 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 Density • Overdense region modifies observed flux from region dV • Relate Lya fluctuations to overdensities • W(k) is a weighted average Barkana & Loeb 2005 W_K plot - stars/ X-rays

23. Determining the first sources Chuzhoy & Shapiro 2006 Sources Ja,* vs Ja,X Spectra aS

24. Summary: Lya • Including correct atomic physics is important for extracting astrophysical information from 21cm fluctuations • Lya fluctuations dominate 21 cm signal at high z • Can be used to determine major source of Lya photons • Intermediate scales give information on X-ray spectrum • Constrain bias of sources at high z • Probe early star formation • Poisson fluctuations may also be interesting

25. 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

26. 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

27. d dV X-ray heating • X-rays provide dominant heating source in early universe(shocks possibly important very early on) • X-ray heating usually 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

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

29. TK fluctuations • Fluctuations in gas temperature can be substantial • Uniform heating washes out fluctuation on small scales • Inhomogeneous heating amplifies fluctuation on large scales • Amplitude of fluctuations contains information about IGM thermal history

30. TK<Tg Angle averaged power spectrum TK>Tg m2 part of power spectrum Indications of TK • When TK<Tgvery different formfrom Lya • Dm2 can be negative which is clear indication of bT <0 (trough) • Existence of featureswill help constrain astrophysical parameters

31. 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

32. X-ray background? • X-ray background at high z is poorly constrained • Decreasing fX helps separates different fluctuations • Also changes shape of Lya power spectrum • If heating is late might see temperature fluctuations with first 21 cm experiments

33. Summary: TK • Inhomogeneous X-ray heating leads to significant fluctuations in gas temperature • Temperature fluctuations track heating rate fluctuations, but lag somewhat behind • Gas temperature fluctuations contain information about the thermal evolution of the IGM before reionization • bT<0 leads to interesting peak-trough structure • Structure will assist astrophysical parameter estimation • 21cm observations at high-z may constrain spectrum and luminosity of X-ray sources

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

35. 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

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

37. 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

38. Observations poor angular resolution foregrounds • Need SKA to probe these brightnessfluctuations • Observe scalesk=0.025-3 Mpc-1 • Easily distinguishtwo models • Probably won’t seetrough :(

39. 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 For more details see astro-ph/0607234 & astro-ph/0508381

40. The end