“First Light” From New Probes of the Dark Ages

and Reionization

Judd D. Bowman (Caltech)Judd D. Bowman (Caltech)Hubble Fellows Symposium 2008Hubble Fellows Symposium 2008

Redshifted 21 cm mean brightness temperature

Furlanetto 2006

50 mK

0 z = 8, xi = 0.3

Data provided by A. Mesinger & S. Furlanetto

Redshifted 21 cm anisotropies

CMB analogy

COBE CMB Blackbody

(Fundamental paradigm)

WMAP

(Elaborate on standard paradigm)

Complications

1. Terrestrial radio frequency interference (RFI) from TV, FM, and other transmitters

2. Ionospheric distortions of sky positions

3. Astrophysical foregrounds (dominated by Galactic synchrotron emission and extragalactic continuum sources)

Astrophysical Foregrounds

• Sun• Galactic emission: 200 to 10,000 K (~70%)• Extragalactic point sources: 30 to 70 K (~25%)• Galactic radio recombination lines: < 1 K • Free-free in IGM: minimal• (21 cm: < 35 mK)

All continuum foregrounds have spectrally smooth power-law profiles

de Oliveira-Costa et al. 2008

Intensity [K]

Spectral indexT

Running of spectral index

Foreground Strategy

Wang et al. 2006

Wolleben et al. 2006

• 100 times more intense at 150 MHz• Faraday rotation adds significant spectral structure• Enters intensity measurement through mis-calibration

1.4 GHz polarized intensity

Pathfinder experiments under construction:

Global AnisotropyEDGES MWA (W. Australia)CoRE (Ron Ekers) LOFAR (Neatherlands)

GMRT (India)PAPER (W. Australia)

Approach: Start from scratch with new instruments that exploit modern digital signal processing technology to address these challenges

EDGES

Experiment to Detect the Global EOR Signaturewith Alan E. E. Rogers (MIT/Haystack Observatory)

Mean (Global) Brightness Temperature

Furlanetto 2006

Frequency derivative

Mean brightness temperature

Instrumental requirements: Do not introduce non-smooth features into the measured the spectrum

Simplifications: Ionospheric distortions and polarized foreground greatly reduced for all-sky measurements

Frequency

Tant

Reflections: multi-path

Frequency

Tant

Reflections: impedance mismatch

Frequency

Tant

ADC LNA

Sampling artifacts

Frequency

Tant

ADC LNAComparison

source

EDGES

balun

“Four-point” antenna

Ground screen

ADC

Amplifiers and switch

EDGES “First Light”

First measured spectrum

partially calibrated, western Australia

1.5 sky hours

Bowman et al. 2008

EDGES: SmoothnessResiduals after 7th order

polynomial fit to spectrum

Measured rms = 75 mK(Instrumentally limited)

rms vs. integration time

Black line: smoothed to 2.5 MHz

Bowman et al. 2008

EDGES: Upper Limit

Upper limit: T21 < 450 mK for instantaneous

reionization at z = 8

z

T21

zr = 8

Expected 21 cm rms 7.5 mK

Bowman et al. 2008

Implications and Future Work

• Preliminary constraint:T21 < 450 mK (if reionization occurred abruptly at z 8)

• Demonstrated viable approach First run within order of magnitude (75 mK [rms] compared to 7.5 mK)

• Clear path to improve performanceAnalog to digital converter identified as limiting componentIncrease bandwidth of antenna impedance match

• Should determine duration of reionization or constrain to: z 2 or better

• May be able to detect heating transition of IGM and/or exotic PBHs

MWA

Murchison Widefield ArrayMIT, Harvard/CfA, Australian Consortium, WA government, RRI (India)

MWA

The VLA in a new way…

• Collecting area: 8000 m2

• Spectral coverage: 80 to 300 MHz• Instantaneous bandwidth: 32 MHz (z = 2)• Spectral resolution: 10 kHz (40 kHz)• 512 antenna “tiles” within 1.5 km diameter• Field of view: 100 to 1000 deg2

• Angular resolution: 3 to 10 arcmin• Sky noise dominated

MWA: Antenna Tile

25

1

2

3

+ 480 more by early 2009

The Catalog of MWA Antennae

MWA: EOR Observing Plan

K

Primary field: RA 60.00, Dec -30.00 1250 hours availableDivided between 2 bands6 < z < 9

Secondary field:RA 155.00, Dec -10.00, 450 hours available6 < z < 7

8 G

pc(1

000

pixe

ls)

1 Gpc [6<z<9](6000 channels)

Zahn et al. 2007

z = 7.68xi=0.33

z = 8.16xi=0.11

z = 6.89xi=0.52

MWA:Data Cube

MWA: Thermal Uncertainty

Bowman et al. 2006

z = 6 z = 8 z = 10 z = 12xi <0.1

Lidz et al. 2008

MWA: Antenna Distribution

• 125000 baselines• 10% in tightly packed core• Completely sample uv-plane within 500 wavelengths• Short baselines probe both large and small spatial scales

Antenna layout Baseline distribution Rotation synthesis

MWA Schedule

• 1/16th collecting area installed, digital systems coming next month

• First engineering run: August 2008– 100 hours on primary field w/ 32 tiles, 32 MHz– Test calibration, all-sky map, polarized sources, RRLs

• Complete array in early 2009

• Science observing mid-2009 through 2010

• Pathfinder experiments for both global and anisotropy signals are in progress to demonstrate foreground mitigation and detect signal at z > 6

• Feasible and compelling near-term science goals to determine redshift (xi <0.1 @ z8) and duration of reionization (z > 2 @ z<13)

Summary