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On the Doorstep of Reionization Judd D. Bowman California Institute of Technology August 27, 2009

On the Doorstep of Reionization Judd D. Bowman California Institute of Technology August 27, 2009. Redshifted 21 cm global signal E xperiment to D etect the G lobal E poch of Reionization S ignature (EDGES) EDGES latest results. The History of Hydrogen Gas. Image: Scientific American 2006.

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On the Doorstep of Reionization Judd D. Bowman California Institute of Technology August 27, 2009

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  1. On the Doorstep of ReionizationJudd D. BowmanCalifornia Institute of TechnologyAugust 27, 2009

  2. Redshifted 21 cm global signal Experiment to Detect the Global Epoch of Reionization Signature (EDGES) EDGES latest results

  3. The History of Hydrogen Gas Image: Scientific American 2006

  4. When did reionization occur? How long did it last? Furlanetto, Oh, & Briggs 2006

  5. 21 cm Overview • Spin-flip hyperfine transition of neutral hydrogen =21 cm (rest-frame), =1420 MHz At z = 6: =1.5 m, = 203 MHz At z = 15: =3.4 m, = 89 MHz 5’9” = 1.75 m  z=7.3 • Use CMB as a “backlight”, then brightness temperature is:

  6. Spin, TS CMB Kinetic Ionized fraction xi = 1 - xHI Mean brightness temperature Pritchard & Loeb 2008

  7. Localized bubbles Bubbles grow and merge… Ionizing photons escape… • On local scales, • a more complex picture • Reionization fronts • X-ray background • UV backgrounds xHI=0.89 xHI=0.18 xHI=0.53 xHI=0.74 z = 10 z = 7.25 z = 8.25 z = 9 100 Mpc 100 Mpc 100 Mpc 100 Mpc Mesinger & Furlanetto Mesinger & Furlanetto Mesinger & Furlanetto Mesinger & Furlanetto

  8. Local patchy evolution… MWA’s objective Early times (z > 15) Primarily density fluctuations 5 arcmin Ionized regions Late times (z < 6) Furlanetto et al. 2004

  9. Big Bang! Today  [MHz] 10 50 100 500 50 0 -50 -100 Tb [mK] 21 cm global brightness temperature 100 10 z [redshift] Pritchard & Loeb 2008

  10. Modeling reionization history The main astrophysical parameters are: - Number of ionizing photons per baryon in star formation - Escape fraction of ionizing photons from galaxies (probably between 0.02 and 0.2) - Star forming efficiency by mass (uncertain to order of magnitude) - Number of Ly- photons per baryon in stars (popII) (uncertain to a factor of few) - X-ray luminosity relative to value extrapolated from Glover and Brand (uncertain to more than order of magnitude) N_ion f_esc f_star f_lya f_xray

  11. Modeling reionization history Code from J. Pritchard

  12. 21 cm global vs. local science Key reionization-era science questions: • When did reionization occur? • What sources were responsible for reionization? • Properties of ionizing sources; connect galaxy-scale physics to large-scale events by e.g. anti-correlation of 21 cm maps with galaxy formation (near-IR surveys) • How did the cosmic web evolve? • Topological transition from ionized bubbles into the filamentary web seen in Ly-alpha forest • How did first quasars form? What were their properties? • Large HII regions, even after quasars dormant, able to image and constrain emission mechanisms, lifetimes, luminosity function, evolution • When did first black holes form? What were their properties? • X-ray heating of IGM near galaxies hosting first black holes and supernovae produces distinctive features in power spectrum (troughs, large amplitudes), z~15 • How does radiative feedback affect high-z galaxy formation? • Directly probe UV and X-ray backgrounds in IGM that regulate star formation and its end products, structure formation, clumping. Soft-UV background z>15 decouples 21 cm spin temperature from CMB See decadal science review: “Astrophysics from the Highly-Redshifted 21 cm Line”, Furlanetto et al. (2009)

  13. 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 • In principle, a simple experiment: No imaging required! • Signal fills aperture of any antenna – a single dipole is sufficient • Ignore ionospheric distortions • Ignore polarized foregrounds • The only feasible 21 cm probe of the Dark Ages (z>15) IGM for the next decade

  14. 2. Experiment to Detect the Global Epoch of Reionization Signature (EDGES) with Alan E. E. Rogers (MIT/Haystack)

  15. All-sky radio spectrum (100-200 MHz) RFI All-sky spectrum • Total spectrum components: • Diffuse Galactic (200K to >1000K) • - Synchrotron (99%) • - Free-free (1%) • Sun (variable) • Extragalactic sources (~50K) • CMB (2.7K) • Galactic RRLs (< 1 K) • 21 cm (10 mK) Instrument bandpass 21 cm global signal

  16. EDGES approach • Trade-off: Compared to MWA, we’ve lost extreme difference in spectral coherence between foreground and signal • Constrain the derivativeof the 21 cm brightness temperature contribution to <1 mK/MHz between 50 and 200 MHz Frequency derivative Mean brightness temperature Furlanetto 2006

  17. EDGES block diagram AEER

  18. balun Analog electronics enclosures “Four-point” antenna Ground screen

  19. in from antenna 2nd stage amp LNA calibration source switch to digitizer dithering noise source to 2nd stage

  20. Acqiris DP310: 12-bit, 420 MS/s in from frontend voltage supply bandpass filter/ analog electronics

  21. RFI trailer CSIRO “hut” MWA fiber

  22. RFI trailer antenna

  23. Murchison Radio-Astronomy Observatory, Boolardy Station, Western Australia

  24. Radio Frequency Interference (RFI)

  25. US radio “pollution”

  26. West Forks, Maine (Jan 2009)

  27. Orbcom LEO satellite constellation

  28. Site selection: Local environment (< 1 mK) Antenna beam pattern: CasA (1400 Jy)  ~50 K

  29. Comparison Switch Scheme • 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

  30. The Joy of Calibration 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

  31. EDGES: Antenna Impedance Match

  32. EDGES: Absolute Calibration • Fully calibrated, • western Australia • = 2.5  0.1 (3 sigma) • Tgal = 237  10 K (3 sigma) @ 150 MHz • Long cable between antenna & LNAs • to measure reflection coefficient in situ Rogers & Bowman 2008

  33. EDGES: Drift Scans Rogers & Bowman 2008

  34. 3. EDGES Latest Results

  35. Measured spectrum Murchison Radio-Astronomy Observatory (MRO) Jan 25 – Feb 14, 2009 10 days: - 50 wall-clock hours on sky - ~7 integrated hours

  36. Integration… rms vs. time w/ baseband removal

  37. Characterizing progress Jan/Feb 2009 Bowman et al. 2008 Green = 100 kHz Black = 2 MHz 75 mK rms – systematic limited 19 mK rms – thermally limited

  38. Model fitting • Polynomial term: • Simple step model of reionization: 2 science parameters: T21 and 0 12 nuisance parameters: an (ACKK!!) to account for impedance mismatch + galactic spectrum “instantaneous” reionization T21

  39. Model fitting

  40. Confidence intervals on T21 (as of February 2009) z=13 z=6 < 90 mK reionization barrier 68% 99% • Constraints scale linearly with thermal noise • Low-level RFI contamination apparent?

  41. Confidence intervals on T21 (as of last night!) reionization barrier

  42. 21 cm derivative: constraints and forecasts z=6 z=13 z=25 NOT reionization… absorption Current fastest plausible reionization worst-case anticipated systematic limit Integrate + improve bandpass

  43. EDGES status & future work • Current: • 19 mK rms in measured spectrum • 21 cm step constrained to <90 mK between 7<z<10 • 21 cm derivative <40 mK / MHz between 7<z<10 (w/ caveats) • Aug-Dec 2009: unattended deployment • Cross 30 mK reionization “barrier” to rule out rapid reionization • The next 3 years (funded by NSF!): • Replace digital backend with Berkeley CASPER open architecture boards for high throughput, but performance • 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

  44. A final thought… HI“Observation of a Line in the Galactic Radio Spectrum: Radiation from Galactic Hydrogen at 1,420 Mc./sec”“Doc” Ewen & Purcell 1951 CMB “A Measurement of Excess Antenna Temperature at 4080 Megacycles per Second” Penzias & Wilson 1965 EoR First detection of reionization?… Bowman & Rogers????

  45. The end This scientific work uses data obtained from the Murchison Radio-astronomy Observatory. We acknowledge the Wajarri Yamatji people as the traditional owners of the Observatory site.

  46. EDGES: Site Selection Variations on the Radar Equation… Scattered sky noise: Scattered receiver noise: Couple spectral structure in scattering coefficient, , to spectrum Structure + ripple

  47. EDGES: Combined xHI Limits Dunkley et al. 2008 Furlanetto, Oh, & Briggs 2006

  48. 21 cm landscape - science • Inflationary physics and cosmology 30 < z < 200 46 >  > 7 MHz • Probe of the matter power spectrum at very small scales ℓ > 104 to 106 • Perturbations to primordial power spectrum and spatial curvature: ns ,  • Neutrino masses, non-Gaussianity, etc. • Baryon collapse • Reionization and the Dark Ages 6 < z < 30 203 >  > 46 MHz • Spin and kinetic temperature history of the IGM • Reionization history, Stromgren spheres (quasar proximity zones) • Star formation history / models for ionizing sources • Abundance of mini-halos • Magnetic fields in IGM • Cosmology • Large scale structure/galaxy evolution z < 6 1420 >  > 203 MHz • Dark Energy through BAOs, cosmology, neutrino masses, etc. • HI in galaxies/halos, masses of DLAs at z = 3 • Indirectly see helium reionization

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