1. The Dawn of 21 cm Cosmology with EDGES Judd D. Bowman Caltech Alan E. E. Rogers Haystack Observatory

2. 21 cm cosmology Image: Scientific American 2006 75% Hydrogen (by mass)

3. 21 cm hyperfine line of hydrogen For a cloud of hydrogen gas between us and a radiation source, 21 cm scattering changes the observed brightness temperature: Universal radiation source: Cosmic Microwave Background standard model cosmology neutral fraction local over-density spin temperature

4. 21 cm Background “Science with the MWA” Greenhill, Bowman, et al. (2010, in prep) Figure by Matt McQuinn

5. Science, Vol. 325. no. 5948, pp. 1617 – 1619, 25 September 2009

6. Kinetic CMB Ionized fraction x i = 1 - x HI Mean brightness temperature Spin, T S Pritchard & Loeb 2008

7. Why global 21 cm? Straightforward probe of mean neutral fraction and HI gas temperatures (spin + kinetic) Star formation history, galaxy evolution, early feedback mechanisms, etc. Direct constraint on redshift and duration of reionization “Simpler” than imaging/power spectrum – Average over large solid angle – Signal fills aperture of any antenna – a single dipole is sufficient – Ignore ionospheric distortions – Polarized foregrounds reduced The only feasible probe of the Dark Ages (z>15) IGM for at least the next decade

8. Foregrounds for 21 cm cosmology Milky Way – synchrotron emission 100-1000 K @ 200 MHz Haslam et al. (1982) Foregrounds |21 cm| [MHz] z T F ( )  

9. Experiment to Detect the Global Epoch of Reionization Signature (EDGES)

10. RFI trailer Antenna EDGES Spectral band: 90-205 MHz Spectral resolution:13 kHz FOV:~80 deg (FWHM) Dynamic range:>10 6

11. EDGES block diagram

12. Bowman & Rogers (in prep)

13. Comparison-switched spectrometer 3-position switch to measure (cycle every 10s): Solve for antenna temperature: (T cal > T L  300 K, T A  250 K, T R  20 K) Limitations: – Total power differences between T L and T A produce residuals – Temporal variations: comparing measurements distinct different times

14. Antenna (p2) Internal load (p0) Noise source (p1) p1– p0 p2 – p0 “Calibrated” sky spectrum T_A ~ (p2 – p0) / (p1 – p0) “Calibrated” sky spectrum w/ RFI filtering and integration Comparison-switched spectrometer

15. EDGES Latest Results

16. Measured spectrum Murchison Radio-Astronomy Observatory (MRO) Aug 20 – Oct 20, 2009 1440 wall-clock hours on sky ~500 hours after RFI filtering ~50 hours actual integration

17. Total power in band vs. time (Aug 23, 2009) Average antenna temperature 90-205 MHz

19. Systematic free performance level: RMS =30 mK in 13 kHz channels (thermal) ~5 mK in 2 MHz bins 20 Oct 2009 Integration… rms vs. time w/ baseband removal Integration time [hours] RMS [K]

20. Model fitting Polynomial term: Simple step model of reionization: 3 science parameters: T 21, , and 0 12 nuisance parameters: a n (ACKK!!) “instantaneous” reionization  T 21 to account for impedance mismatch + galactic spectrum

21. Was reionization instantaneous? Fit for T 21 with fixed  = ∞ Test all 0

22. Confidence intervals on T 21 with fixed = reionization barrier October 2009 yellow: 68% gray: 95% Bowman & Rogers (in prep)

23. Bowman et al. 2008 Pace of progress February 2009August 2009September 2009 yellow: 68% gray: 95% reionization barrier

24. How long was reionization? Fit for  with fixed T 21 = CDM Test all 0

25. Confidence intervals on dx/dz with fixed T 21  Δz  > 0.2  Δz  > 0.4 Bowman & Rogers (in prep)

26. 21 cm derivative: constraints and forecasts Feb 2009 anticipated systematic limit (no/low RFI) Integrate + improve bandpass Oct 2009 z=13z=6z=25 NOT reionization… absorption

27. Summary Concluded 3 month deployment in MRO – Deepest broadband spectrum ever acquired: 5 mK rms – Instantaneous reionization ruled out: 21 cm rapid step constrained to <30 mK between 6<z<13 – First direct dx i /dz constraints on diffuse IGM The next step: – Upgrade digital backend; exploring Berkeley CASPER open architecture boards for high throughput – Redesign antenna to improve impedance match (use lower order polynomial for continuum removal) – Attempt detection of z>15-25 absorption feature to “set clock” for interpreting reionization

28. The end