Cosmology with the 21 cm Transition

1. Cosmology with the 21 cm Transition Steve Furlanetto Yale University September 25, 2006

2. Outline • The 21 cm transition • The Dark Ages • First Light • Reionization • Measuring the Matter Power Spectrum • Summary See our Physics Reports review (Furlanetto, Oh, & Briggs 2006, astro-ph/0608032) for more information!

3. The 21 cm Transition • Map emission (or absorption) from IGM gas • Dark Ages: only probe! • Spectral line: measure entire history • Direct measurement of IGM properties SF, AS, LH (2004)

4. The Spin Temperature • In the absence of coupling mechanisms, TS=TCMB • Collisions couple TS to TK • Efficient when d > 15 [10/(1+z)]2 if relatively hot • Dominated by electron exchange in H-H collisions in neutral medium (Zygelman 2005), or H-e- collisions in partially ionized medium (Furlanetto & Furlanetto 2006) • The Wouthuysen-Field Effect • Pump triplet state with absorption/re-emission of Ly photons • Becomes effective when ~0.1 Ly photon/baryon

5. Observing the Signal • The Challenges • Terrestrial radio frequency interference • Ionospheric “seeing” • Foregrounds • Instrumental issues (polarization leakage, sidelobe control,…) • Noise so large, imaging extremely difficult! LOFAR

6. Error Estimates: z=8 • Survey parameters • z=8 • Tsys=440 K • tint=1000 hr • B=6 MHz • No systematics! • MWA (solid black) • Aeff=7000 m2 • 1.5 km core • SKA (dotted blue) • Aeff=1 km2 • 5 km core MWA SKA Foreground limit after McQuinn et al. (2005)

7. Error Estimates: z=12 • Survey parameters • z=12 • Tsys=1000 K • tint=1000 hr • B=6 MHz • No systematics! • MWA (solid black) • Aeff=9000 m2 • 1.5 km core • SKA (dotted blue) • Aeff=1 km2 • 5 km core MWA SKA Foreground limit

8. The Global Signal:The Dark Ages • Straightforward physics • Fluctuations directly trace matter power spectrum (Loeb & Zaldarriaga 2004) • 3D dataset • Small-scale power SF, PO, FB (2006)

9. The Dark Ages: Dark Matter Decay Dark matter decay models ~1016 yr ~1019 yr Standard calculation SF, PO, EP (2006)

10. The Global Signal:First Light • First stars (quasars?) flood Universe with photons • Heating • W-F effect • Ionization • Timing depends on f*, fesc, fX, stellar population feedback weak X-rays Pop II Stars SF (2006)

11. The Ly and Heating Eras • Ly photons create fluctuations around first sources (Barkana & Loeb 2004, Pritchard & Furlanetto 2006) • X-rays seed fluctuations in TS (and hence Tb) • Discrete (biased) sources and 1/r2 flux • Soft X-rays have shorter mean free paths • Rapid structure formation Pritchard & Furlanetto (2006)

12. 21 cm Observations: Reionization z=18.3 13 Mpc comoving Dn=0.1 MHz SF, AS, LH (2004)

13. 21 cm Observations: Reionization z=16.1 13 Mpc comoving Dn=0.1 MHz SF, AS, LH (2004)

14. 21 cm Observations: Reionization z=14.5 13 Mpc comoving Dn=0.1 MHz SF, AS, LH (2004)

15. 21 cm Observations: Reionization z=13.2 13 Mpc comoving Dn=0.1 MHz SF, AS, LH (2004)

16. 21 cm Observations: Reionization z=12.1 13 Mpc comoving Dn=0.1 MHz SF, AS, LH (2004)

17. 21 cm Observations: Reionization z=11.2 13 Mpc comoving Dn=0.1 MHz SF, AS, LH (2004)

18. 21 cm Observations: Reionization z=10.4 13 Mpc comoving Dn=0.1 MHz SF, AS, LH (2004)

19. 21 cm Observations: Reionization z=9.8 13 Mpc comoving Dn=0.1 MHz SF, AS, LH (2004)

20. 21 cm Observations: Reionization z=9.2 13 Mpc comoving Dn=0.1 MHz SF, AS, LH (2004)

21. 21 cm Observations: Reionization z=8.7 13 Mpc comoving Dn=0.1 MHz SF, AS, LH (2004)

22. 21 cm Observations: Reionization z=8.3 13 Mpc comoving Dn=0.1 MHz SF, AS, LH (2004)

23. 21 cm Observations: Reionization z=7.9 13 Mpc comoving Dn=0.1 MHz SF, AS, LH (2004)

24. 21 cm Observations: Reionization z=7.5 13 Mpc comoving Dn=0.1 MHz SF, AS, LH (2004)

25. 21 cm Observations: Reionization z=9.2 13 Mpc comoving Dn=0.1 MHz SF, AS, LH (2004)

26. The Power Spectrum • Rich set of information from bubble distribution: • Timing: growth of structure • Underlying source population (SF, MM, LH 2005) • Uniform ionizing component (SF, MZ, LH 2004b) • Feedback (SF, MZ, LH 2004b) • Correlation with density field (SF, MZ, LH 2004b) • Also must consider higher-order statistics! xi=0.59 xi=0.78 xi=0.69 xi=0.48 xi=0.36 xi=0.13 z=10

27. Fundamental Cosmology? • Probably a period where density dominates before reionization: measure matter power spectrum • Modest improvements to small scales (neutrinos, tilt, etc.; McQuinn et al. 2005, Bowman et al. 2005) • Redshift space distortions • Anisotropic: can extract matter power spectrum (Bharadwaj & Ali 2004, Barkana & Loeb 2004) SF (2006)

28. Anisotropic Power Spectrum: Error Estimates at z=8 • Survey parameters • z=8 • Tsys=440 K • tint=1000 hr • B=6 MHz • No systematics! • MWA (solid black) • Aeff=7000 m2 • 1.5 km core • SKA (dotted blue) • Aeff=1 km2 • 5 km core MWA SKA Foreground limit after McQuinn et al. (2005)

29. Conclusions • The 21 cm line is a unique probe of the high-redshift universe • Reionization: measures distribution of ionized gas and its relation to sources, at every redshift • First Light: measures the impact of these sources on their environment • Dark Ages: “clean” probe of cosmology and of exotic processes like dark matter decay See our Physics Reports review (Furlanetto, Oh, & Briggs 2006, astro-ph/0608032) for more information!