the dawn of 21 cm cosmology with edges judd d. bowman caltech alan e. e. rogers haystack observatory

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