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21 cm cosmology

The Dawn of 21 cm Cosmology with EDGES Judd D. Bowman Caltech Alan E. E. Rogers Haystack Observatory. 21 cm cosmology. 75% Hydrogen (by mass). WFC3/HUDF09, z = 7-8. Illingworth. Image: Scientific American 2006. 21 cm hyperfine line of hydrogen.

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21 cm cosmology

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  1. The Dawn of 21 cm Cosmology with EDGESJudd D. BowmanCaltechAlan E. E. RogersHaystack Observatory

  2. 21 cm cosmology 75% Hydrogen (by mass) WFC3/HUDF09, z = 7-8 Illingworth Image: Scientific American 2006

  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 local over-density spin temperature neutral fraction

  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. Spin, TS CMB Kinetic Ionized fraction xi = 1 - xHI Mean brightness temperature 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 z Milky Way – synchrotron emission 100-1000 K @ 200 MHz Foregrounds |21 cm|  [MHz] TF()   Haslam et al. (1982)

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

  10. EDGES Spectral band: 90-205 MHz Spectral resolution: 13 kHz FOV: ~80 deg (FWHM) Dynamic range: >106 RFI trailer Antenna

  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: (Tcal > TL 300 K, TA 250 K, TR  20 K) • Limitations: • Total power differences between TL and TA produce residuals • Temporal variations: comparing measurements distinct different times

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

  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

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

  19. Model fitting • Polynomial term: • Simple step model of reionization: 3 science parameters: T21, , and 0 12 nuisance parameters: an (ACKK!!) to account for impedance mismatch + galactic spectrum “instantaneous” reionization T21

  20. Was reionization instantaneous? Fit for T21 with fixed  = ∞ Test all 0

  21. Confidence intervals on T21 with fixed = October 2009 reionization barrier yellow: 68% gray: 95% Bowman & Rogers (in prep)

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

  23. How long was reionization? Fit for  with fixed T21 = CDM Test all 0

  24. Confidence intervals on dx/dz with fixed T21 Δz> 0.2 Δz> 0.4 Bowman & Rogers (in prep)

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

  26. 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 dxi/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

  27. The end

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