EDGES: The ‘Global’ Perspective Judd D. Bowman (Caltech) Alan E. E. Rogers (MIT/Haystack) Jacqueline N. Hewitt (MIT) Rennan Barkana (Tel Aviv) Peng Oh (UCSB) January 20, 2009

21 cm Emission Early times (z > 15) Late times (z < 6) Furlanetto et al. 2004

Global 21 cm z / z  1%   1 MHz T  1 mK  1 to 100 hours Brightness temperature, T21 Fractional signal, T21 / Tgal * Pritchard z / z  1%   1 MHz T  1 mK  1 to 100 hours > 1000 (z > 50) Dynamic Range T21/Tgal  10-5

Why global 21 cm? Straightforward probe of mean ionization 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 Ignore ionospheric distortions Polarized foregrounds reduced Foregrounds easier to model (less precision required) The only feasible probe of the Dark Ages (z>15) for at least the next decade

EDGES: Approach Constrain the derivative of the 21 cm brightness temperature contribution to <1 mK/MHz between 50 and 200 MHz Frequency derivative Mean brightness temperature Furlanetto 2006

EDGES: Technique

EDGES: System Overview

EDGES: System Overview balun ADC “Four-point” antenna Amplifiers, switch, and comparison source Ground screen

From antenna LNA Switch Noise source To 2nd stage

Acqiris AC240: 8-bit, 1 GS/s

EDGES: Spectral smoothness First measured spectrum partially calibrated, western Australia 1.5 sky hours Bowman, Rogers & Hewitt 2008

(Bad and not-so-good) sites Haystack (D1) West Forks, Maine

West Forks, Maine (last week)

EDGES: Instrumental limit Residuals after 7th order polynomial fit to spectrum rms vs. integration time Measured rms = 75 mK (Instrumentally limited) Expected 21 cm = 25 mK Black line: smoothed to 2.5 MHz Bowman, Rogers & Hewitt 2008

Residuals from the “not-so-good” site (West Forks, Maine) 126 mK rms Smoothed to 13 MHz 11th –order polynomial (120-205 MHz) Blue lines = RFI But this is amazing because our first system had 1 K residuals at this site!

Current & forecasted performance z=6 z=30 Bowman et al. 2008 (bench-test, July 2008) (bench-test, Dec 2008) NEXT WEEK?! 2011 2009 Acqiris DP310 backend + dithering noise source Full implementation CASPER ROACH backend

Bu can you really do it?

First detection of 21 cm line in the Milky Way “Observation of a Line in the Galactic Radio Spectrum: Radiation from Galactic Hydrogen at 1,420 Mc./sec” “Doc” Ewen & Purcell 1951

Discovery of Cosmic Microwave Background “A Measurement of Excess Antenna Temperature at 4080 Megacycles per Second” Penzias & Wilson 1965

?

End

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

EDGES: Drift scans Rogers & Bowman 2008

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

End