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

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

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

?? 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 before reionization CMB temperature Knowing TCMB=2.726 K and assuming thermal coupling by Compton scattering followed by adiabatic expansion allows informed guess of high z temperature evolution

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

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 Lyman a 11S1/2 Selection rules: DF= 0,1 (Not F=0F=0) 10S1/2

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… Remember to smile Pritchard & Furlanetto 2006 Hirata 2006

Lyman b gg Optically thick to Lyman series 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

Lyman g gg Cascade via 3S and 3D levels allows production of Lyman a frecycle,g=0.26 Higher transitions frecycle,n~ 0.3 gg

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

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

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

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

Global history Furlanetto 2006 + + Heating + HII regions + IGM Adiabatic expansion + X-ray heating + Compton heating expansion Heating 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

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

Thermal history Temperature outside of HII regions

21 cm fluctuations Twilight Dark Ages Z* Za ZT ZR Z30 Density Z~150 Baryon Density W-F Coupling Velocity gradient Brightness temperature Neutral fraction Gas Temperature Cosmology Reionization X-ray sources Lya sources Cosmology Twilight Dark Ages Z* Za ZT ZR Z30 Density Z~150 Collisionally coupled regime No 21 cm signal Ly X-ray UV Comment on information the different P_mu contain Reionization TS~Tg

Angular separation? Baryon Density W-F Coupling Velocity gradient Neutral fraction Gas Temperature In linear theory, peculiar velocities correlate with overdensities Bharadwaj & Ali 2004 Anisotropy of velocity gradient term allows angular separation Comment on information the different P_mu contain Barkana & Loeb 2005 Initial observations will average over angle to improve S/N

21 cm fluctuations Twilight Dark Ages Z* Za ZT ZR Z30 Density Z~150 Baryon Density W-F Coupling Velocity gradient Brightness temperature Neutral fraction Gas Temperature Cosmology Reionization X-ray sources Lya sources Cosmology Twilight Dark Ages Z* Za ZT ZR Z30 Density Z~150 Collisionally coupled regime No 21 cm signal Ly X-ray UV Comment on information the different P_mu contain Reionization TS~Tg

Reionization Z=12.1 Z=9.2 Z=8.3 Z=7.6 Neutral fraction Gas Temperature W-F Coupling Velocity gradient Density Lya coupling saturated HII regions large IGM hot TK>>Tg Z=12.1 Z=9.2 Z=8.3 Z=7.6 Usual case that people consider and first target of observations Ignore spin temperature fluctuation and consider ionization fluc Furlanetto, Sokasian, Hernquist 2003

21 cm fluctuations: Lya Neutral fraction Gas Temperature W-F Coupling Velocity gradient Density -negligible heating of IGM -tracks density IGM still mostly neutral Lya flux varies Lya fluctuations unimportant after coupling saturates (xa>>1) Comment that opposite case to reionization Ignore ionization fluc and consider spin temperature fluctuations 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

Fluctuations from the first stars d dV 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

Determining the first sources da dominates bias source properties density Chuzhoy, Alvarez, & Shapiro 2006 Sources Ja,* vs Ja,X Lya flux weighted average of contributions from stars and X-rays Spectral distinctions can be determined Pritchard & Furlanetto 2006 Spectra aS z=20 D=[k3P(k)/2p]1/2

21cm fluctuations: TK Neutral fraction Gas Temperature W-F Coupling Velocity gradient Density coupling saturated IGM still mostly neutral density + x-rays In contrast to the other coefficients bT can be negative Comment on information the different P_mu contain Sign of bT constrains IGM temperature Pritchard & Furlanetto 2006

Temperature fluctuations TS~TK<Tg Tb<0 (absorption) Hotter region = weaker absorption bT<0 TS~TK~Tg Tb~0 21cm signal dominated by temperature fluctuations TS~TK>Tg Tb>0 (emission) Hotter region = stronger emission bT>0

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 d dV adiabatic index -1 Barkana & Loeb 2005

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

TK fluctuations Fluctuations in gas temperature can be substantial Amplitude of fluctuations contains information about IGM thermal history Difference between uniform and inhomogeneous heating can be substantial

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

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

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

21 cm fluctuations: z ? Exact form very model dependent

Redshift slices: Lya z=19-20 Pure Lya fluctuations

Redshift slices: Lya/T z=17-18 Growing T fluctuations lead first to dip in DTb then to double peak structure Double peak requires T and Lya fluctuations to have different scale dependence

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

Redshift slices: T/d z=13-14 After TK>Tg , the trough disappears As heating continues T fluctuations die out Xi fluctuations will start to become important at lower z

Observations Need SKA to probe these brightness fluctuations poor angular resolution foregrounds Need SKA to probe these brightness fluctuations Observe scales k=0.025-2 Mpc-1 Easily distinguish two models Probably won’t see trough :(

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 fluctuations in future simulations For more details see astro-ph/0607234 & astro-ph/0508381

Extra Slides

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

21 cm basics 21 cm brightness temperature 21 cm spin temperature

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

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 d dV

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