29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

1

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

2

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

3

The End Of the ‘Dark Ages’: new telescopes

shedding new light

Rachel WebsterUniversity of Melbourne

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

4

Outline

• Brief History of Hydrogen• What is Reionisation?• New Telescopes: MWA (&

others)

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

5

Outline

• Brief History of Hydrogen• What is Reionisation?• New Telescopes: MWA (&

others)Acknowledgements to a long list of collaborators, including:David Barnes, Frank Briggs, Jackie Hewitt, Colin Lonsdale, Miguel Morales, Stuart Wyithe

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

6

History of the universe:

Miralda-Escude 2003

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

7

History of the universe

JWST

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

8

History of the universe

JWST& MWA

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

9

PrimordialFluctuations

First Stars

Galaxies andClusters

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

10

Evolution of structure

Z=28.6

AndreyKravtsov

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

11

Structure at z=10

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

12

Local Cosmic Web:

HICAT, Meyer atal 2004

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

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What is Reionisation?

Ly- Ly-

Low z: long mean free path for Ly- (1216Å) and photo-ionizing photons (<912Å)

High z: short mean free path for Ly- (1216Å) and photo-ionizing photons (<912Å)

HIHI

HII

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

14

Spin Temperature: absorption or emission?

• Definition of spin temperature: Given the number of atoms in each of the

hyperfine transition levels of HI,

• Spin temp and CMB temp equal at early times

• Later kinetic temp Tk of gas increases; spin temp coupled to Tk by scattering of Ly photons;

21cm emission

ST

T

n

n *

0

1 exp3 07.0/10* khT

CMBs TT

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

15

Z = 20 15 10 8 7 6

coldHI

HII

< 1 (Gunn-Peterson Effect)

70 MHz 90 MHz 130 160 190 MHz

Lowest possible redshift for reionisation

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

16

Quasars Before Reionisation

3/2

sHI

5s 10

z1106.5τ

x

reionz1A1216o

sourcez1A1216o

HI absorbs photons near Ly- resonance

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

17

Quasars Before Reionisation

3/2

sHI

5s 10

z1106.5τ

x

reionz1A1216o

sourcez1A1216o

HI absorbs photons near Ly- resonance

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

18

• Gunn-Peterson troughs give the overlap redshift for HII at 6<zreion<6.4

• The IGM has a neutral fraction xHI>0.001 at z~6

Fan et al. (2001)Becker et al. (2001)

The data

Gunn-Peterson Trough(total absorption)

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

19

Z = 20 15 10 8 7 6

coldHI

HII

70 MHz 90 MHz 130 160 190 MHz

Highest likely redshift for reionisation

warmHI

WMAP z=15-20

Correlation between polarisation and temperature on large angular scales due to Thomson scattering by electrons

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

20

Detection Expt I: ‘the step’

Shaver etal 1999

Plenty of signal; can the featurebe separated from the bandpass?

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

21

Experiment II: ‘Strömgren Spheres’

HI at IGM temperature

HI warmed by X-rays

HII (no contrast)

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

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CMB+quasar+foreground

IGMOr ∆z along the line of sight

z along the line-of-sight

Contrast measures xHI

Wyithe & Loeb 2003

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

23

Measuring the size of ‘Strömgren spheres’

skmVc /3300~~0

MpcR

HRV

p

p

5.4~

Ly- at z=6.28

White et al. (ApJ 2003)

source

HI

HII

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

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Detection Expt III: ‘power spectrum’

Morales &Hewitt 2004

alsoZaldarriagaetal 2004

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

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Neutral hydrogen is opaque

TheoreticalSimulation:NickGnedin2005

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

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Early structure was simple

• Theorist’s heaven: excellent progress• Modelling of Stromgren spheres provides

new limits on neutral fraction at z~6: >0.1

tq~106 yrtq~107 yr

Wyithe, Loeb, Carilli 2004

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

27

But it was never going to be easy….

**Foreground radio emission (noise ~102-5 xsignal)

» Synchrotron and free-free emission from MW

(Shaver etal 1999)» Low frequency radio point sources

(Di Matteo etal 2004)

» Free-free emission from IGM electrons(Oh

1999)

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

28

‘Noise’ spectra smooth in frequency robust removal

Santos, Cooray & Knox 2005

Power spectrum

noise

bias x ionisation fraction

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

29

New Telescopes: history

Clarke Lake Radio Obs

Bill Erikson and hisstudents

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

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New Experiments

• LOFAR – Holland» (Partially) funded, lots of momentum

• PaST - China (Mongolia)» On the ground, collecting data

• LWA - SW USA» Still planning; below 90MHz spread over

400km

• MWA - Western Australia» US-Australian collab, seeking funding

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

31

New Experiments

• LOFAR – Holland» (Partially) funded, lots of momentum

• PaST - China (Mongolia)» On the ground, collecting data

• LWA - SW USA» Still planning; below 90MHz spread over

400km

• MWAMWA - Western Australia- Western Australia» US-Australian collab, seeking fundingUS-Australian collab, seeking funding

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

32

MWA Collaboration

• Project leaders: MIT & MIT-Haystack(technical and scientific)

• Harvard/CFA (scientific)• ATNF(technical)• Melbourne (early deployment &

scientific)• ANU-RSAA, Tasmania (scientific)• Curtin, UWA, OSI (local infrastructure &

scientific)

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

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Experiments with MWA

• EoR– Stromgren spheres– Power spectrum

• Transients• Coronal Mass Ejections

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

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Simulated Stromgren Spheres: LFD

100 Hours

1000 Hours

z=6.5,

R=4Mpc

Stu Wyithe, Loeb, Barnesastro-ph/0506045

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

35

Full Array ie 10xLFD

100 Hours

1000 Hours

There are 10’s of Stromgren Spheresin the field-of-view larger than 4Mpc

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

36

Detecting the Power Spectrum with MWA (Bowman & Morales 2005)

Ionized frac. = 0.6

=0

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

37

The SUNCoronal Mass Ejections: measure interplanetaryscintillation and Faraday rotation to describethe behaviour of the solar wind from near the sun tothe earth’s location

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

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Effect of space weather

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

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Why Western Australia?

FORTE satellite 131 MHZ

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

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Mileura Homestead

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

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The road to Mileura

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

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Early Deployment Site

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

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Tile assembly

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

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Tile 1 from the air

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

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RFI Environment

30-60 minuteintegrations overfull bandpass

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

46

Sun at 96 MHzYes, that is the FM band …

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

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Interferometry on an AGN

time

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

48

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

49

Galactic Centre at 108MHz

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

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Specs for MWA-LFD

• Frequency range: 80-300MHz, 32MHz bandwidth[3.8<z(21cm)<16.9]

• 500 tiles 4x4 dipoles in ‘phased array’, 8000m2

• Field-of-view: ~25deg fully steerable, multibeam• Area: 1.5km giving 3.4 arcmins @ 200MHz• 125,000 baselines, 4x109visibilities/0.5sec,

full stokes polarisation

[FPGA-based massively parallel digital hardware]http://web.haystack.mit.edu/arrays/MWA

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

51

Finally……• Tomography of the earliest

structures in universe• Novel `technology telescope’• cheap array design • huge, fast data network• huge collecting area• stunning radio-quiet location

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

52

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

53

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

54

Strömgren Spheres Expand Faster into Partially Reionised IGM

High neutral fraction:Slow expansion

Low neutral fraction:Fast expansion

neutral IGM ionised IGM

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

55

ground basedradio techniques

10 MHz

350

MWA-LFDMWA-LFD

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

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29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

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furlanetto

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

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ciardi

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

59

ciardi

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

60NASA

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

61

The Surface of Bubble Overlap

• There is a surface on the sky corresponding to the redshifts along different lines of sight where the IGM was most recently partially neutral

Contribution from HII regions

Morales & Hewitt (2004)

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

62

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

63

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

64

Numerical Simulations of Reionization (Gnedin et al. 2000)

neutral H fraction ionizing intensity

4Mpc << 60Mpc

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

65

Structure on Angular Scales in Emission from the Cosmic Web

• The temperature map, and the size of fluctuations on different scales reveal the topology of reionisation

Tozzi et al. (ApJ 2002)

29 June 2005

Caroline Herschel Distinguished Lecture

Rachel Webster

66

Numerical Simulations of Reionization (Gnedin et al. 2000)

neutral H fraction ionizing intensity

neutral H fraction

ionizing intensity

4Mpc << 60Mpc