Résumé / Abstract Journal-club_Postdoc

Journal-club Postdoc

« Strong gravitational lensing in cosmology »

Aleksandra Piórkowska
Postdoc - Dept. Physique, Univ. Silésie (Katowice, Pologne)

One of the most important issues in modern cosmology is the problem of present accelerating expansion of the Universe inferred from the supernovae (SNIa) Hubble diagram and supported by other independent studies including: CMBR anisotropies or baryon acoustic oscillations imprinted in the large scale structure power spectrum. The explanation of this phenomenon is far from obvious and in the lack of clear theoretical guidance we are left with phenomenological approach based on upgrading observational fits of quantities which parametrize the unknown (such like density parameters or coefficients in the cosmic equation of state) and seeking for coherence among alternative tests and techniques. In this context stong gravitational lensing systems appear to be promising.
The use of strong lensing systems as a tool to study dark energy equation of state has become a serious technique in modern cosmology. First application of this method was done on n=20 lenses (Biesiada, Pio´rkowska & Malec, 2010). Now, we have the compilation of n=118 such systems, carefully selected from SLACS, SL2S and BELLS ongoing surveys (and this will grow further due to inclusion of new lenes from ongoing SL2S survey). We use this larger sample to demonstrate that strong lensing data provide a good quality tool for constraining the values of cosmological parameters like those in dark energy equation of state. We focused ourselfes on two cosmological scenarios explaining observed present accelerating expansion of the Universe - XCDM cosmology where dark energy is represented by an unknown kind of fluid with barotropic equation of state in which: i) w parameter has a constant value and ii) w parameter is allowed to evolved with redshift according to Chevalier-Polarski- Linder parametrization (w(z) = w0 + w1 * (z/(1+z))). In our work we assume two models of mass distribution in lensing galaxies: SIS model with isothermal profile and more general one with arbitrary power-law index gamma (allowing it also to evolve wth redshift gamma(z)).
Our results are in agreement both with w and gamma values obtained by other authors and also shows a trend of being complementary to latest supernova Ia data.
mardi 26 mai 2015 - 11:00
Salle des séminaires Évry Schatzman, Institut d'Astrophysique
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