From Supernovae to

Baryon Acoustic Oscillations

Patrice OKOUMA

Supervisor : Prof. Bruce A. BASSETT

UCT

Dec. 2008 SKA Postgraduate Bursary Conference

Overview

Theoretical Work Observational Work Data Analysis

Adiabatic &

Isocurvature modeson BAO

Type-Ia Supernovae

MeerKAT /SKASALT

A Type-Ia Supernovae (SNe Ia) -------> Explosion of a White Dwarf having accreted mass from a companion star, beyond a critical threshold known as the Chandrasekhar limit (~ 1.4 Solar masses).

A reminder

Silicon Line

Folatelli (2004)

SNe Ia as standardizable candle

Krisciunas et al., 2005

Spectral characterization of Type-Ia supernovae via chi-squared based techniques and cross- correlation approach (SNID by Blondin et al. 2006)

------------> M.Sc.

A past work

chi-squared approach

cross-correlation approach (SNID code)

2-week campaign for Infra red light curves of Sne Ia (IRSF, Sutherland, SA)

Work with Ariel Goobar & al. (Sweden)

Extinctions corrections for optical observations -----> Major uncertainty in

using SNe Ia for cosmology

•In NIR, SNe-Ia are still standardizable candles ( Krisciunas et al., 2005 )

•Smaller extinction corrections

•Strong evidence for a weaker lightcurve width-brightnesscorrection

Lower error budget

Better constraints on the Cosmology

2-week campaign for optical spectra of Sne (1.9-m telescope, Sutherland, SA)

Work with . Y. Fang & al. (Michigan,US); A. Goobar et al. (Sweden)

Goals :

Training;

Testing simultaneous identification of transients from ROTSE (http://www.rotse.net/),in Gamsberg (southern Namibia).

Theoretical Work Observational Work Data Analysis

Adiabatic &

Isocurvature modeson BAO

Supernovae

MeerKAT / SKASALT

Number density and/or energy density

characterize cosmological species in the early Universe.

Linear perturbations of these quantities are

The Early Universe through Baryon Acoustic Oscillations Work with K. Moodley et al. (UKZN,SA) & C. Zunckel (Princeton, US)

METRIC perturbations Eqs. for evolution of perturbations

THEN

Adiabatic modes are perturbations affecting cosmological species such that :

Isocurvature modes :

CMB (for flat Universe) ===> Adiabatic modes are dominant BUTBUT ~ 10% Isocurvature modes are allowed (in early Universe).

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Therefore,

If we assume Adiabatic fluctuations, what do we get wrong about Dark Energy ... and ... by how much ?

Baryon Acoustic Oscillations (B.A.O) = Pathfinder

Initial fluctuations in density and gravitational potential drive acoustic waves in the fluid:compressions and rarefactions.

At early times the universe was hot, dense and ionized. Photons and matter were tightly coupled by Thomson scattering.

An (adiab.) evolution in a spherically symmetric shell of plasma

Another prediction verified !!!

Eisenstein et al. (2005)detect the theorized “bump” in the 2-point correlation function of the SDSS -LRG at z ~ 0.35

From CMBFrom CMB

Possible effects of Isocurvature modesPossible effects of Isocurvature modes

r0

Theory/Model Control with data

Feedback

Simulation

(classical) Program

√

Simulations using CAMB (code )

Mixture

Cross-correlation Pk

Correlation coeff.

= -1 : anti-correlation

= 1 : full correlation

else : partial correlation

Divide both

Totally correlated

Partially correlated

Zoom

Strong “degeneracy” with Dark Energy

via BAO

Immediate perspective

Perspective (cont'd) : Fisher formalism on Pk

Seo & Eisenstein (2007) approach <--

Future work & preliminary conclusion

BAO are a rapidly maturing methodfor investigating Dark Energy -----> Huge collaboration opportunities.

•Highly robust method. •Complimentary to Supernova cosmology

Applicability and scalability to MeerKAT / SKA …

MeerKat TBD 15-20 000 ~ 1 Million Ongoing

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THANK YOU