1. Baryon Acoustic Oscillations
Renée Hlozek
Bruce Bassett
Yabebal Fantaye, Jacques Kotze

2. Baryon Acoustic Oscillations
Eisenstein et al. 2005
Tegmark et al. 2005
Who will detect the BAO in the radio?

3. 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!

4. SKA will provide stunning BAO constraints
SKA will provide stunning BAO constraints.  review the BAO forecasts for the SKA using Fisher4Cast.

5. The Birth of Cosmic Ripples
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.
The Birth of Cosmic Ripples
RECOMBINATION
Eisenstein

6. The Birth of Cosmic Ripples
Following a pebble in the cosmic pond…
BARYON DENSITY
PHOTON DENSITY
MASS PROFILE
White & Eisenstein

7. The Birth of Cosmic Ripples
BARYON DENSITY
PHOTON DENSITY
MASS PROFILE
The dark matter is slow to move – it only interacts gravitationally
White & Eisenstein

8. The Birth of Cosmic Ripples
BARYON DENSITY
PHOTON DENSITY
MASS PROFILE
Photons and baryons move outward together, the radius of the shell moving at
White

9. The Birth of Cosmic Ripples
z=1081: just before decoupling
BARYON DENSITY
PHOTON DENSITY
MASS PROFILE
The dark matter begins to follow the baryons
White

10. The Birth of Cosmic Ripples
BARYON DENSITY
PHOTON DENSITY
MASS PROFILE – PHOTONS and BARYONS only
Lack of pressure support `freezes’ the radius of oscillation into baryon density
White

11. The Birth of Cosmic Ripples
BARYON DENSITY
PHOTON DENSITY
MASS PROFILE – PHOTONS and BARYONS only
White

12. The Birth of Cosmic Ripples
BARYON DENSITY
PHOTON DENSITY
MASS PROFILE
Dark matter continues to move slowly – towards baryon peak
White

13. The Birth of Cosmic Ripples
BARYON DENSITY
PHOTON DENSITY
MASS PROFILE
Dark matter distribution now clusters around baryon peak.
White

14. The Cosmic RULER
Final 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

15. Distance and Expansion
transverse
radial

16. Many pebbles in the pond
But in reality there are superimposed rings of power
Bassett and RH, 2008

17. Enemies of the BAO
Shot Noise
Bassett and RH, 2008

18. Enemies of the BAO Cosmic Variance
Bassett and RH, 2008
We need lots of galaxies (N > 106) and large volume (V > 0.5 h-3Gpc3)

19. SKA BAO
Blake et al. 2005

20. Intuitive ERROR ELLIPSES
Data should all be the same – don’t regenerate new data.
Try the panels side side
Fisher4Cast

21. SKA DE Constraints 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?

22.
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