From Supernovae to Baryon Acoustic Oscillations
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From Supernovae to
Baryon Acoustic Oscillations
Patrice OKOUMA
Supervisor : Prof. Bruce A. BASSETT
UCT
Dec. 2008 SKA Postgraduate Bursary Conference
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Overview
Theoretical Work Observational Work Data Analysis
Adiabatic &
Isocurvature modeson BAO
Type-Ia Supernovae
MeerKAT /SKASALT
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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)
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SNe Ia as standardizable candle
Krisciunas et al., 2005
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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
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chi-squared approach
cross-correlation approach (SNID code)
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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
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•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
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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).
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Theoretical Work Observational Work Data Analysis
Adiabatic &
Isocurvature modeson BAO
Supernovae
MeerKAT / SKASALT
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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
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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).
S. W
hite
(2
008
)
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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.
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An (adiab.) evolution in a spherically symmetric shell of plasma
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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
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From CMBFrom CMB
Possible effects of Isocurvature modesPossible effects of Isocurvature modes
r0
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Theory/Model Control with data
Feedback
Simulation
(classical) Program
√
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Simulations using CAMB (code )
Mixture
Cross-correlation Pk
Correlation coeff.
= -1 : anti-correlation
= 1 : full correlation
else : partial correlation
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Divide both
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Totally correlated
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Partially correlated
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Zoom
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Strong “degeneracy” with Dark Energy
via BAO
Immediate perspective
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Perspective (cont'd) : Fisher formalism on Pk
Seo & Eisenstein (2007) approach <--
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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
F. C
ombe
s (2
00
6)
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THANK YOU
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