Baryon Acoustic Oscillations

BARYON ACOUSTIC OSCILLATIONS

RENÉE HLOZEKBruce BassettYabebal Fantaye, Jacques Kotze

Baryon Acoustic OscillationsEisenstein et al. 2005 Tegmark et al. 2005

Who will detect the BAO in the radio?

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!

SKA will provide stunning BAO constraints.

review the BAO forecasts for the SKA using Fisher4Cast.

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

The Birth of Cosmic RipplesFollowing a pebble in the cosmic pond…

White & Eisenstein

PHOTON DENSITYBARYON DENSITY MASS PROFILE

The Birth of Cosmic Ripples

The dark matter is slow to move – it only interacts gravitationally

PHOTON DENSITYBARYON DENSITY MASS PROFILE

White & Eisenstein

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

The Birth of Cosmic Ripples

White

The dark matter begins to follow the baryons

z=1081: just before decoupling

PHOTON DENSITYBARYON DENSITY MASS PROFILE

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

The Birth of Cosmic Ripples

White

PHOTON DENSITYBARYON DENSITY MASS PROFILE – PHOTONS and BARYONS only

The Birth of Cosmic Ripples

White

PHOTON DENSITYBARYON DENSITY MASS PROFILE

Dark matter continues to move slowly – towards baryon peak

The Birth of Cosmic Ripples

White

PHOTON DENSITYBARYON DENSITY MASS PROFILE

Dark matter distribution now clusters around baryon peak.

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(~

Distance and Expansion

radial

transverse

• But in reality there are superimposed rings of power

Many pebbles in the pond

Bassett and RH, 2008

Enemies of the BAOShot Noise

Bassett and RH, 2008

Enemies of the BAOCosmic Variance

We need lots of galaxies (N > 106) and large volume (V > 0.5 h-3Gpc3)Bassett and RH, 2008

SKA BAO

Blake et al. 2005

Intuitive ERROR ELLIPSES

Fisher4Cast

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

www.cosmology.org.za• Open source, modular and battle-tested GUI designed using software engineering principles

• Approximately 400 downloads since May 2008

• Planned Extensions: lensing, CMB, direct radio survey support

• Encourage Collaboration and Extensions