“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