Cosmological constraints from Baryonic Acoustic Oscillations observed with SDSS-III / BOSS
IN2P3 - CNRS Astroparticule and Cosmologie
Mercredi 10/04/2013, 14:15
Salle Claude Itzykson, Bât. 774, Orme des Merisiers
I will present the measurement of the large scale structure of galaxies recently published by the BOSS (Baryon Oscillations Spectroscopic Survey), one of the instruments of SDSS-III (Sloan Digital Sky Survey). The corresponding cosmological constraints confirm the agreement between observations and a flat Universe dominated by a cosmological constant.
The galaxy sample used, called CMASS, contains more than 250000 galaxies covering the largest volume ever observed with such a high density.
BOSS has measured the two-point correlation function and the power spectrum of this sample, using a technique allowing to reconstruct the density field and allowing to detect baryonic acoustic oscillations (BAO) with a significance of five standard deviations.
We have used the apparent BAO scale to measure the ratio between our distance to z=0.57 and the sound horizon: D_V/r_s=13.67 +/- 0.22. With 1.7% uncertainty, this is the most accurate measurement ever obtained with a galaxy survey. Placing this measurement on the Hubble diagram along with other measurements shows excellent agreement with other probes and confirms the agreement between observations and the Lambda-CDM model.
BAO have also been recently detected by BOSS at a redshift of 2.31 using measurements of the neutral hydrogen density in the Lyman-alpha forest of 48000 background quasars. This result further confirms the agreement between Lambda-CDM and observations and provides for the first time a measurement of the expansion rate of the Universe before it started accelerated expansion, while Dark Energy was not yet the dominant component in the Universe.