1. 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

2. 21 cm Emission Early times (z > 15) Late times (z < 6)
Furlanetto et al. 2004

3. 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

4. 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

5. 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

6. EDGES: Technique

7. EDGES: System Overview

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

9. From antenna
LNA
Switch
Noise
source
To 2nd stage

10. Acqiris AC240: 8-bit, 1 GS/s

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

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

13. West Forks, Maine
(last week)

14. 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

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

16. 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

17. Bu can you really do it?

18. 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

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

20. ?

21. End

22. 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

23. EDGES: Drift scans
Rogers & Bowman 2008

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

25. End