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

1.Redshifted 21 cm global signal 2.Experiment to Detect the Global Epoch of Reionization Signature (EDGES) 3.EDGES latest results

The History of Hydrogen Gas Image: Scientific American 2006

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

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:

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

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

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

Big Bang! Today Pritchard & Loeb z [redshift] T b [mK] 21 cm global brightness temperature  [MHz]

Modeling reionization history The main astrophysical parameters are: N_ion f_esc f_star f_lya f_xray - 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)

Modeling reionization history Code from J. Pritchard

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) 21 cm global vs. local science

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

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

All-sky spectrum 21 cm global signal All-sky radio spectrum ( MHz) RFI Instrument bandpass 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)

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

AEER EDGES block diagram

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

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

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

RFI trailer MWA fiber CSIRO “hut”

antenna RFI trailer

Murchison Radio-Astronomy Observatory, Boolardy Station, Western Australia

Radio Frequency Interference (RFI)

US radio “pollution”

West Forks, Maine (Jan 2009)

Orbcom LEO satellite constellation

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

Comparison Switch Scheme 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

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 The Joy of Calibration

EDGES: Antenna Impedance Match

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

EDGES: Drift Scans Rogers & Bowman 2008

3. EDGES Latest Results

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

Integration… rms vs. time w/ baseband removal

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

Model fitting Polynomial term: Simple step model of reionization: 2 science parameters: T 21 and 0 12 nuisance parameters: a n (ACKK!!) “instantaneous” reionization  T 21 to account for impedance mismatch + galactic spectrum

Model fitting

Confidence intervals on T 21 (as of February 2009) Constraints scale linearly with thermal noise Low-level RFI contamination apparent? 68% 99% z=13z=6 < 90 mK reionization barrier

Confidence intervals on T 21 (as of last night!) reionization barrier

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

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

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 ???? A final thought…

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.

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

EDGES: Combined x HI Limits Furlanetto, Oh, & Briggs 2006 Dunkley et al. 2008

21 cm landscape - science Inflationary physics and cosmology 30  > 7 MHz Probe of the matter power spectrum at very small scales ℓ > 10 4 to 10 6 Perturbations to primordial power spectrum and spatial curvature: n s,  Neutrino masses, non-Gaussianity, etc. Baryon collapse Reionization and the Dark Ages 6  > 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  > 203 MHz Dark Energy through BAOs, cosmology, neutrino masses, etc. HI in galaxies/halos, masses of DLAs at z = 3 Indirectly see helium reionization