On the Doorstep of Reionization Judd D. Bowman (Caltech) March 11, 2009 DIY 21 cm cosmology

1.When was reionization? 2.How long did it last? time Zahn et al Each map is 65.6 Mpc h -1 per side

Neutral fraction (x HI ) history Furlanetto, Oh, & Briggs 2006 time

Global (average) 21 cm signal =21 cm (rest-frame), =1420 MHz At z = 6: =1.5 m, = 200 MHz At z = 13: =3.0 m, = 100 MHz

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

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

All-sky spectrum 21 cm contribution RFI Instrument bandpass Reionization

Challenges Need to separate signal from foregrounds with high dynamic range – Differences in spectral structure less significant for global signal than for fluctuations – Much less information available to help with separation Difficult instrumental problem: – Hard to calibrate absolute response to better than 1% – No empty fields for comparison (on/off target) – Transient RFI changes instrumental response and requires highly linear analog-to-digital sampling – Antenna frequency-dependence difficult to isolate

Experiment to Detect the Global EOR Signature (EDGES) With: Alan E. E. Rogers (MIT-Haystack)

EDGES: Approach 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

EDGES: Approach Advantages of measuring dT 21 /d – Detailed sky model unnecessary: use low-order polynomial to fit foreground component and subtract – Reduces need for absolute calibration – Instrument allowed to introduce smooth spectral structures since they will be fit-out by polynomial – Viable for detecting reionization and Dark Ages absorption feature Drawback – Reduced information return, not full T 21 (z)

EDGES: System Overview AEER

“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

EDGES: Differential Measurement 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) Calibrates internal spectral structure (except antenna) Limitations: differences between T L and T A produce residuals, comparing measurements from different times

EDGES: Site Selection (< 1 mK) Antenna beam pattern: CasA (1400 Jy)  ~50  K

Radio frequency interference Annotated by F. Briggs

West Forks, Maine (Jan 2009)

Murchison Radio-Astronomy Observatory, Boolardy Station, Western Australia It never rains in the desert…

antenna “The trailer” – receiver

Measured spectrum Murchison Radio-Astronomy Observatory (MRO) Boolardy Station, Western Australia Jan 25 – Feb 14, days, 50 sky hours

Integration… rms vs. time

Bins… rms vs. spectral resolution

Characterizing progress Bowman et al. 2008Current 75 mK rms – systematic limited 19 mK rms – thermally limited Green = 100 kHz Black = 2 MHz

Constraints on T 21 Fit polynomial + Rapid reionization model w/  z = nuisance parameters (polynomial coefficients) 1 model parameter  T 21 (21 cm step height)  T 21 < 90 mK Constraints scale linearly with thermal noise 68% 99% reionization model Low-level RFI contamination z=13z=6

Constraints on 21 cm derivative Current Integrate to expected systematic limit Integrate + improve bandpass fastest plausible reionization z=13z=6z=25 NOT reionization… absorption

Summary Global 21 cm measurements offer direct route to fundamental reionization science (x HI, T S ) and unique opportunity to detect high-redshift 21 cm absorption Faster, cheaper, but not trivial EDGES empirical limits best to date on 21 cm emission (T 21 < 90 mK) and first measurement of low-frequency radio spectrum at ~10 mK level EDGES should do much better in near future

The end

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