First light from new probes of the dark ages and reionization
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Judd D. Bowman (Caltech) Hubble Fellows Symposium 2008. “First Light” From New Probes of the Dark Ages and Reionization. Redshifted 21 cm mean brightness temperature. Furlanetto 2006. Redshifted 21 cm anisotropies. 50 mK. 0 . z = 8, x i = 0.3 Data provided by

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First light from new probes of the dark ages and reionization l.jpg

Judd D. Bowman (Caltech)

Hubble Fellows Symposium 2008

“First Light” From New Probes of the Dark Ages and Reionization



Redshifted 21 cm anisotropies l.jpg
Redshifted 21 cm anisotropies

50 mK

0

z = 8, xi = 0.3

Data provided by

A. Mesinger & S. Furlanetto


Cmb analogy l.jpg
CMB analogy

WMAP

(Elaborate on standard paradigm)

COBE CMB Blackbody

(Fundamental paradigm)


Complications l.jpg
Complications

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

  • Ionospheric distortions of sky positions

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


Astrophysical foregrounds l.jpg
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


Slide7 l.jpg

Intensity [K]

Spectral index

T  

Running of

spectral index

de Oliveira-Costa et al. 2008


Foreground strategy l.jpg
Foreground Strategy

Wang et al. 2006


Slide9 l.jpg

1.4 GHz polarized intensity

  • 100 times more intense at 150 MHz

  • Faraday rotation adds significant spectral structure

  • Enters intensity measurement through mis-calibration

Wolleben et al. 2006


Slide10 l.jpg

Pathfinder experiments under construction:

GlobalAnisotropy

EDGES 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 l.jpg

Experiment to Detect the Global EOR Signature

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

EDGES


Mean global brightness temperature l.jpg
Mean (Global) Brightness Temperature

Mean brightness temperature

Frequency derivative

Furlanetto 2006


Slide13 l.jpg

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


Slide14 l.jpg

Tant

Frequency


Slide15 l.jpg

Reflections: multi-path

Tant

Frequency


Slide16 l.jpg

Reflections: impedance mismatch

Tant

Frequency

ADC

LNA


Slide17 l.jpg

Sampling artifacts

Tant

Frequency

ADC

Comparison source

LNA


Edges18 l.jpg
EDGES

balun

ADC

“Four-point” antenna

Amplifiers and switch

Ground screen


Edges first light l.jpg
EDGES “First Light”

First measured spectrum

partially calibrated,

western Australia

1.5 sky hours

Bowman et al. 2008


Edges smoothness l.jpg
EDGES: Smoothness

Residuals after 7th order polynomial fit to spectrum

rms vs. integration time

Measuredrms = 75 mK

(Instrumentally limited)

Black line: smoothed to 2.5 MHz

Bowman et al. 2008


Edges upper limit l.jpg
EDGES: Upper Limit

Upper limit: T21 < 450 mK for instantaneous

reionization at z = 8

z

T21

Expected 21 cm rms 7.5 mK

zr = 8

Bowman et al. 2008


Implications and future work l.jpg
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 performance

    Analog to digital converter identified as limiting component

    Increase 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


Slide23 l.jpg

Murchison Widefield Array

MIT, Harvard/CfA, Australian Consortium, WA government, RRI (India)

MWA


Slide24 l.jpg
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



Slide26 l.jpg

The Catalog of MWA Antennae

+ 480 more by early 2009


Mwa eor observing plan l.jpg
MWA: EOR Observing Plan

Primary field:

RA 60.00, Dec -30.00

1250 hours available

Divided between 2 bands

6 < z < 9

Secondary field:

RA 155.00, Dec -10.00,

450 hours available

6 < z < 7

K


Mwa data cube l.jpg

1 Gpc [6<z<9]

(6000 channels)

MWA:Data Cube

8 Gpc

(1000 pixels)

z = 7.68

xi=0.33

z = 8.16

xi=0.11

z = 6.89

xi=0.52

Zahn et al. 2007


Mwa thermal uncertainty l.jpg
MWA: Thermal Uncertainty

xi <0.1

z = 6

z = 8

z = 10

z = 12

Lidz et al. 2008

Bowman et al. 2006


Mwa antenna distribution l.jpg
MWA: Antenna Distribution

Antenna layout

Baseline distribution

Rotation synthesis

  • 125000 baselines

  • 10% in tightly packed core

  • Completely sample uv-plane within 500 wavelengths

  • Short baselines probe both large and small spatial scales


Mwa schedule l.jpg
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


Summary l.jpg
Summary

  • 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 @ z8) and duration of reionization (z> 2 @ z<13)