Baryon Acoustic Oscillations
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Transcript of Baryon Acoustic Oscillations
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BARYON ACOUSTIC OSCILLATIONS
RENÉE HLOZEKBruce BassettYabebal Fantaye, Jacques Kotze
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Baryon Acoustic OscillationsEisenstein et al. 2005 Tegmark et al. 2005
Who will detect the BAO in the radio?
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MeerKAT may be the first.
Need to be ready to do the analyses before the telescope is operational
useful to review the key ideas.
It should!
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SKA will provide stunning BAO constraints.
review the BAO forecasts for the SKA using Fisher4Cast.
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The Universe is neutral.
Photons free-stream away
- no longer interact with ions.
Pressure support is removed.
Baryon wave stalls.
The Universe is ionized.
Photons and ions interact via Thomson scattering.
Perturbations in the cosmic plasma oscillate as acoustic waves.
R
ECOM
BINA
TION
Eisenstein
The Birth of Cosmic Ripples
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The Birth of Cosmic RipplesFollowing a pebble in the cosmic pond…
White & Eisenstein
PHOTON DENSITYBARYON DENSITY MASS PROFILE
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The Birth of Cosmic Ripples
The dark matter is slow to move – it only interacts gravitationally
PHOTON DENSITYBARYON DENSITY MASS PROFILE
White & Eisenstein
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The Birth of Cosmic Ripples
White
Photons and baryons move outward together, the radius of the shell moving at
)4/31(3 b
cv
PHOTON DENSITYBARYON DENSITY MASS PROFILE
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The Birth of Cosmic Ripples
White
The dark matter begins to follow the baryons
z=1081: just before decoupling
PHOTON DENSITYBARYON DENSITY MASS PROFILE
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The Birth of Cosmic Ripples
White
PHOTON DENSITYBARYON DENSITY MASS PROFILE – PHOTONS and BARYONS only
Lack of pressure support `freezes’ the radius of oscillation into baryon density
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The Birth of Cosmic Ripples
White
PHOTON DENSITYBARYON DENSITY MASS PROFILE – PHOTONS and BARYONS only
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The Birth of Cosmic Ripples
White
PHOTON DENSITYBARYON DENSITY MASS PROFILE
Dark matter continues to move slowly – towards baryon peak
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The Birth of Cosmic Ripples
White
PHOTON DENSITYBARYON DENSITY MASS PROFILE
Dark matter distribution now clusters around baryon peak.
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The Cosmic RULERFinal density
profile peaks at r = 0 - with a second peak at a distance that depends on Ωm and h.
• This is the baryon acoustic peak
Mpctzc 130~26.3/000,4001100~)1(~
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Distance and Expansion
radial
transverse
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• But in reality there are superimposed rings of power
Many pebbles in the pond
Bassett and RH, 2008
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Enemies of the BAOShot Noise
Bassett and RH, 2008
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Enemies of the BAOCosmic Variance
We need lots of galaxies (N > 106) and large volume (V > 0.5 h-3Gpc3)Bassett and RH, 2008
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SKA BAO
Blake et al. 2005
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Intuitive ERROR ELLIPSES
Fisher4Cast
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Two key questions:
What is the best HI survey for the SKA?
How much would a 50% or 20% SKA lose in terms of dark energy?
For e.g. 108 vs 109 galaxies – how much does that affect dark energy constraints?
SKA DE Constraints
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