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Evolution and Application of the 21 cm Signal Throughout Cosmic History

Explore the evolution and application of the 21 cm signal in cosmic history, from high-z radiation backgrounds to first sources. Understand the basics, coupling mechanisms, and thermal history to probe reionization and experimental prospects. Dive into the theoretical and simulation frameworks, determining the first sources and X-ray heating effects on the universe. Discover insights into reionization topology and evolution through 21 cm measurements, highlighting the need for advanced instruments like SKA. Despite uncertainties, the 21 cm signal offers a promising window into understanding early cosmic phenomena.

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Evolution and Application of the 21 cm Signal Throughout Cosmic History

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  1. Evolution and application of the 21 cm signal throughout cosmic history Jonathan Pritchard (CfA-HCO) Collaborators: Steve Furlanetto (UCLA) Avi Loeb (Harvard) Mario Santos (CENTRA - IST) Alex Amblard (UCI) Hy Trac (CfA) Renyue Cen (Princeton) Asantha Cooray (UCI)

  2. Overview • 21 cm as probe of high-z radiation backgrounds • Fluctuations in Lya andX-ray backgrounds lead to 21 cm fluctuations • What might 21 cm observations tell usabout first sources? • Reionization • Experimental prospects z~30 z~12 z~7

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

  4. Wouthuysen-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) l~21 cm 10S1/2

  5. Thermal History e.g. Furlanetto 2006

  6. 21 cm fluctuations W-FCoupling Velocitygradient BaryonDensity Neutralfraction Gas Temperature Brightnesstemperature b Cosmology Reionization X-raysources Lyasources Cosmology Amount ofneutral hydrogen Spin temperature Velocity(Mass)

  7. Angular separation? W-FCoupling Velocitygradient BaryonDensity Neutralfraction Gas Temperature b • 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

  8. Temporal separation? W-FCoupling Velocitygradient BaryonDensity Neutralfraction Gas Temperature Brightnesstemperature b Cosmology Reionization X-raysources Lyasources Cosmology Twilight Dark Ages

  9. d dV continuum injected Fluctuations from the first stars • Fluctuations in flux from source clustering, 1/r2 law, optical depth,… • Relate fluctuations in Lya and X-ray fluxes to overdensities • Start with Lya... Barkana & Loeb 2005 • Three contributions to Lya flux: continuum & injected from stars + x-ray Chen & Miralde-Escude 2006, Chuzhoy & Shapiro 2006, Pritchard & Furlanetto 2006,2007

  10. Determining the first sources da dominates source properties density bias Chuzhoy,Alvarez, & Shapiro 2006 Sources Ja,* vs Ja,X Pritchard & Furlanetto 2007 Spectra aS z=20

  11. X-ray heating • Soft X-rays heat closer to source, hard X-rays have long m.f.p. • X-ray flux -> heating rate -> temperature evolution • Integrated effect - so whole SF history contributes Pritchard & Furlanetto 2007

  12. TK<Tg TK>Tg Indications of TK • Learn about source bias and spectrum in same way as Lya • Constrain heating transition dT dominates

  13. dx dT da ? X-ray background? • To avoid giving the idea of certainty… Extrapolating low-z X-ray:IR correlation gives: Glover & Brand 2003

  14. Reionization Santos, Amblard, JRP, Trac, Cen, Cooray 2008 (100 Mpc/h)3 cube, 18803 particle N-body + UV photon ray tracing X-ray heating and coupling included via simple model

  15. Ionization history WMAP1 WMAP3 Zreion=10.8±1.4 (instant) WMAP5 Zreion~9 ±1.4 (extended) Xi>0.1 zR~7t~0.07

  16. Theory vs Simulation Furlanetto, Zaldarriaga, Hernquist 2004 • Bubbles imprint “knee” on large scales • Limited agreement at end of reionizationon large scales

  17. 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 Foregrounds are thebig problem! SKA: S. Africa/Australia ??? Freq: 60 MHz-35 GHz Baselines: 20m- 3000km More from Judd next

  18. Temporal evolution Post-reionization Reionization Dark ages Signal from denseneutral clumps at low z Pritchard & Loeb 2008

  19. x  T SKA ? MWA Temporal evolution

  20. High-z Observations poor angular resolution foregrounds • Need SKA to probe these brightnessfluctuations • Observe scalesk=0.025-2 Mpc-1 • Easily distinguishtwo models • Optimistic foregroundremoval • B~12MHz ->Dz~1.5

  21. Low-z Observations LOFAR MWA SKA • Low k cutofffrom antennaesize • Sensitivity ofLOFAR and MWA drops off by z=12 McQuinn et al. 2006

  22. MWA SKA LARC Angular Separation Astrophysics Cosmology

  23. Conclusions • Today told a simple story - lots of uncertainty in all attempts at modeling this period • Can use 21 cm to learn about the first luminous sources via the Lya background • Temperature fluctuations should give insight into thermalevolution of IGM • If X-ray heating important, then can learn about early X-ray sources • Map out reionization topology and evolution • Detailed measurements will require SKA and luck • Beginnings of full theoretical framework coming into being • Early days for 21 cm and still unclear what will and will not be possible - foregrounds will be determining factor

  24. Bonus material

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

  26. 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

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

  28. Redshift slices: T/d z=13-14 • After TK>Tg , thetrough disappears • As heating continuesT fluctuations die out

  29. Redshift slices: d/x z=8-12 • Bubbles imprint featureon power spectra once xi>0.2 • Non-linearities in density fieldbecome important (TK fluc. not included)

  30. 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

  31. 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

  32. When did things start?

  33. 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 • Cross-correlation with galaxies also important

  34. Reionization? =0.06 =0.09 =0.12 WMAP1 WMAP3 Zreion~11±1 (instant) WMAP5 Zreion~9 ±1 (model)

  35. 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) • Parameters: fstar, X, N, Nion (+ spectra + bias +…)

  36. Angular Separation

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