On the Doorstep of ReionizationOn the Doorstep of Reionization

Judd D. BowmanJudd D. BowmanCalifornia Institute of TechnologyCalifornia Institute of Technology

August 27, 2009August 27, 2009

1.1. Redshifted 21 cm global signalRedshifted 21 cm global signal

2.2. EExperiment to xperiment to DDetect the etect the GGlobal lobal EEpoch poch of Reionization of Reionization SSignature (EDGES)ignature (EDGES)

3.3. EDGES latest resultsEDGES latest results

The History of Hydrogen Gas

Image: Scientific American 2006

When did reionization occur? How long did it last?

Furlanetto, Oh, & Briggs 2006

21 cm Overview

• Spin-flip hyperfine transition of neutral hydrogen

=21 cm (rest-frame), =1420 MHz

At z = 6: =1.5 m, = 203 MHz

At z = 15: =3.4 m, = 89 MHz

5’9” = 1.75 m z=7.3

• Use CMB as a “backlight”, then brightness temperature is:

mKT

TxzzT

S

CMBHIb

1119, 2/1

KineticCMB

Ionized fraction xi = 1 - xHI

Mean brightness temperature

Spin, TS

Pritchard & Loeb 2008

Localized bubbles

Mesinger & FurlanettoMesinger & Furlanetto

100 Mpc

z = 10xHI=0.89Ionizing photons escape…

Mesinger & FurlanettoMesinger & Furlanetto

100 Mpc

z = 9xHI=0.74Bubbles grow and merge…

Mesinger & FurlanettoMesinger & Furlanetto

100 Mpc

z = 8.25xHI=0.53

Mesinger & Furlanetto

100 Mpc

z = 7.25xHI=0.18On local scales,a more complex picture

•Reionization fronts•X-ray background•UV backgrounds

Local patchy evolution… MWA’s objective

Primarily density fluctuations

Early timesEarly times(z > 15)(z > 15)

Late timesLate times (z < 6)(z < 6)

Ionized regions

Furlanetto et al. 2004

5 ar

cmin

Big

Ban

g! Today

Pritchard & Loeb 2008

100 10 z [redshift]

50

0

-50

-100

Tb [

mK

]

21 cm global brightness temperature

5001005010

[MHz]

Modeling reionization history

The main astrophysical parameters are:

N_ion

f_esc

f_star

f_lya

f_xray

- Number of ionizing photons per baryon in star formation

- Escape fraction of ionizing photons from galaxies(probably between 0.02 and 0.2)

- Star forming efficiency by mass(uncertain to order of magnitude)

- Number of Ly- photons per baryon in stars (popII)(uncertain to a factor of few)

- X-ray luminosity relative to value extrapolated from Glover and Brand (uncertain to more than order of magnitude)

Modeling reionization history

Code from J. Pritchard

Key reionization-era science questions:• When did reionization occur?

• What sources were responsible for reionization?– Properties of ionizing sources; connect galaxy-scale physics to large-scale events by

e.g. anti-correlation of 21 cm maps with galaxy formation (near-IR surveys)

• How did the cosmic web evolve?– Topological transition from ionized bubbles into the filamentary web seen in Ly-alpha

forest

• How did first quasars form? What were their properties?– Large HII regions, even after quasars dormant, able to image and constrain emission

mechanisms, lifetimes, luminosity function, evolution

• When did first black holes form? What were their properties?– X-ray heating of IGM near galaxies hosting first black holes and supernovae produces

distinctive features in power spectrum (troughs, large amplitudes), z~15

• How does radiative feedback affect high-z galaxy formation?– Directly probe UV and X-ray backgrounds in IGM that regulate star formation and its

end products, structure formation, clumping. Soft-UV background z>15 decouples 21 cm spin temperature from CMB

See decadal science review: “Astrophysics from the Highly-Redshifted 21 cm Line”, Furlanetto et al. (2009)

21 cm global vs. local science

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

• In principle, a simple experiment: No imaging required!– Signal fills aperture of any antenna – a single dipole is sufficient– Ignore ionospheric distortions– Ignore polarized foregrounds

• The only feasible 21 cm probe of the Dark Ages (z>15) IGM for the next decade

2.Experiment to Detect the

Global Epoch of Reionization Signature(EDGES)

with Alan E. E. Rogers (MIT/Haystack)

All-sky spectrum

21 cm global signal

All-sky radio spectrum (100-200 MHz)

RFI

Instrument bandpassTotal spectrum components:• Diffuse Galactic (200K to >1000K)

- Synchrotron (99%)

- Free-free (1%)• Sun (variable)• Extragalactic sources (~50K)• CMB (2.7K)• Galactic RRLs (< 1 K)• 21 cm (10 mK)

EDGES approach

• Trade-off: Compared to MWA, we’ve lost extreme difference in spectral coherence between foreground and signal

• 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

AEER

EDGES block diagram

“Four-point” antenna

Ground screen

balun

Analog electronics enclosures

in from antenna

to 2nd stage

calibration source

2nd 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

RFI trailer

MWA fiber

CSIRO “hut”

antenna

RFI trailer

Murchison Radio-Astronomy Observatory, Boolardy Station, Western Australia

Radio Frequency Interference (RFI)

US radio “pollution”

West Forks, Maine (Jan 2009)

Orbcom LEO satellite constellation

Site selection: Local environment

(< 1 mK)

Antenna beam pattern: CasA (1400 Jy) ~50 K

Comparison Switch Scheme

• 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

The Joy of Calibration

EDGES: Antenna Impedance Match

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 & LNAsto measure reflection coefficient in situ

Rogers & Bowman 2008

EDGES: Drift Scans

Rogers & Bowman 2008

3. EDGES Latest Results

Measured spectrum

Murchison Radio-Astronomy Observatory (MRO)

Jan 25 – Feb 14, 2009

10 days:- 50 wall-clock hours on sky- ~7 integrated hours

Integration… rms vs. time w/ baseband removal

19 mK rms – thermally limited

Green = 100 kHzBlack = 2 MHz

Characterizing progress

Jan/Feb 2009 Bowman et al. 2008

75 mK rms – systematic limited

Model fitting

• Polynomial term:

• Simple step model of reionization:

2 science parameters: T21 and 0

12 nuisance parameters: an (ACKK!!)

11

0n

nnap

021 HTm

“instantaneous” reionizationT21

to account for impedance mismatch + galactic spectrum

Model fitting

Confidence intervals on T21 (as of February 2009)

• Constraints scale linearly with thermal noise• Low-level RFI contamination apparent?

68%

99%

z=13 z=6

< 90 mK

reionization barrier

Confidence intervals on T21 (as of last night!)

reionization barrier

21 cm derivative: constraints and forecasts

Current

worst-case anticipated systematic limit

Integrate +improve bandpass

fastest plausible reionization

z=13z=6 z=25

NOT reionization…

absorption

EDGES status & future work

• Current: – 19 mK rms in measured spectrum– 21 cm step constrained to <90 mK between 7<z<10– 21 cm derivative <40 mK / MHz between 7<z<10 (w/ caveats)

• Aug-Dec 2009: unattended deployment– Cross 30 mK reionization “barrier” to rule out rapid reionization

• The next 3 years (funded by NSF!):– Replace digital backend with Berkeley CASPER open architecture

boards for high throughput, but performance– 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

HI“Observation of a Line in the

Galactic Radio Spectrum: Radiation from Galactic

Hydrogen at 1,420 Mc./sec”

“Doc” Ewen & Purcell 1951

CMB“A Measurement of Excess Antenna Temperature at

4080 Megacycles per Second”

Penzias & Wilson 1965

EoRFirst detection of reionization?…

Bowman & Rogers????

A final thought…

The end

This scientific work uses data obtained from the Murchison Radio-astronomy Observatory. We acknowledge the Wajarri Yamatji people as the traditional owners of the Observatory site .

EDGES: Site Selection

Variations on the Radar Equation…

Scattered sky noise:

Scattered receiver noise:

4

G

P

P

R

G

P

P24

Couple spectral structure in scattering coefficient, , to spectrum

Structure + ripple

EDGES: Combined xHI Limits

Furlanetto, Oh, & Briggs 2006 Dunkley et al. 2008

21 cm landscape - science

Inflationary physics and cosmology 30 < z < 200 46 > > 7 MHz• Probe of the matter power spectrum at very small scales ℓ > 104 to 106

• Perturbations to primordial power spectrum and spatial curvature: ns ,

• Neutrino masses, non-Gaussianity, etc.• Baryon collapse

Reionization and the Dark Ages 6 < z < 30 203 > > 46 MHz • Spin and kinetic temperature history of the IGM• Reionization history, Stromgren spheres (quasar proximity zones)• Star formation history / models for ionizing sources• Abundance of mini-halos• Magnetic fields in IGM• Cosmology

Large scale structure/galaxy evolution z < 6 1420 > > 203 MHz • Dark Energy through BAOs, cosmology, neutrino masses, etc.• HI in galaxies/halos, masses of DLAs at z = 3• Indirectly see helium reionization