21 cm cosmology
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The Dawn of 21 cm Cosmology with EDGES Judd D. Bowman Caltech Alan E. E. Rogers Haystack Observatory
description
The Dawn of 21 cm Cosmology with EDGES Judd D. Bowman Caltech Alan E. E. Rogers Haystack Observatory. 21 cm cosmology. 75% Hydrogen (by mass). WFC3/HUDF09, z = 7-8. Illingworth. Image: Scientific American 2006. 21 cm hyperfine line of hydrogen. - PowerPoint PPT Presentation
Transcript of 21 cm cosmology
The Dawn of 21 cm Cosmology with EDGES
Judd D. BowmanCaltech
Alan E. E. RogersHaystack Observatory
21 cm cosmology
Image: Scientific American 2006
75% Hydrogen 75% Hydrogen (by mass)(by mass)
Illingworth
21 cm hyperfine line of hydrogen
• For a cloud of hydrogen gas between us and a radiation source, 21 cm scattering changes the observed brightness temperature:
• Universal radiation source: Cosmic Microwave Background
standard model cosmology
neutral fraction
localover-density
spin temperature
21 cm Background
“Science with the MWA”Greenhill, Bowman, et al. (2010, in prep)
Figure by Matt McQuinn
Science, Vol. 325. no. 5948, pp. 1617 – 1619, 25 September 2009
KineticCMB
Ionized fraction xi = 1 - xHI
Mean brightness temperature
Spin, TS
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
Foregrounds for 21 cm cosmology
Milky Way – synchrotron emission100-1000 K @ 200 MHz
Haslam et al. (1982)
Foregrounds
|21 cm|
[MHz]
z
TF()
Experiment to Detect the Global Epoch of Reionization Signature
(EDGES)
RFI trailerAntenna
EDGESSpectral band: 90-205 MHzSpectral resolution: 13 kHz FOV: ~80 deg (FWHM)Dynamic range: >106
EDGES block diagram
Bowman & Rogers (in prep)
Comparison-switched spectrometer
• 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
Antenna (p2)Internal load (p0)
Noise source (p1)
p1– p0
p2 – p0“Calibrated” sky spectrum
T_A ~ (p2 – p0) / (p1 – p0)
“Calibrated” sky spectrumw/ RFI filtering and integration
Comparison-switched spectrometer
EDGES Latest Results
Measured spectrum
Murchison Radio-Astronomy Observatory (MRO)
Aug 20 – Oct 20, 2009
1440 wall-clock hours on sky~500 hours after RFI filtering ~50 hours actual integration
Total power in band vs. time (Aug 23, 2009)
Average antenna temperature 90-205 MHz
Systematic free performance level:RMS = 30 mK in 13 kHz channels (thermal)
~5 mK in 2 MHz bins
20 Oct 2009
Integration… rms vs. time w/ baseband removal
Integration time [hours]
RMS
[K]
Model fitting
• Polynomial term:
• Simple step model of reionization:
3 science parameters: T21, , and 0
12 nuisance parameters: an (ACKK!!)
11
0n
nnap
021
2
erfcT
m
“instantaneous” reionization
T21
to account for impedance mismatch + galactic spectrum
Was reionization instantaneous?
Fit for T21
with fixed = ∞Test all 0
Confidence intervals on T21 with fixed =
reionization barrier
October 2009
yellow: 68%gray: 95%
Bowman & Rogers (in prep)
Bowman et al. 2008
Pace of progress
February 2009August 2009September 2009
yellow: 68%gray: 95%
reionization barrier
How long was reionization?
Fit for with fixed T21 = CDM
Test all 0
Confidence intervals on dx/dz with fixed T21
Δz> 0.2Δz> 0.4
Bowman & Rogers (in prep)
21 cm derivative: constraints and forecasts
Feb 2009
anticipated systematic limit (no/low RFI)
Integrate +improve bandpass
Oct 2009
z=13z=6 z=25
NOT reionization…
absorption
Summary
• Concluded 3 month deployment in MRO– Deepest broadband spectrum ever acquired: 5 mK rms
– Instantaneous reionization ruled out: 21 cm rapid step constrained to <30 mK between 6<z<13
– First direct dxi/dz constraints on diffuse IGM
• The next step:– Upgrade digital backend; exploring Berkeley CASPER open
architecture boards for high throughput
– 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
The end
