The main objective of the BOSS program is to impose constraints on the properties of black energy. For this, the spectra of 1.5 million red light galaxies and 160 000 quasars are being measured. This will allow accurate detection of acoustic oscillations of baryons.


Baryonic acoustic oscillations

Acoustic oscillations of baryons are one of the most promising ways to achieve the constraints of the properties of black energy. Before decoupling between matter and radiation (CMB emission at z = 1100), the primordial density fluctuations gave rise to pressure (and therefore acoustic) waves in the photon-baryon fluid.

During the decoupling of the radiation, these oscillations are frozen leaving the trace of this acoustic wave in the CMB and in the distribution of the baryons and the black matter. This trace is now found as a characteristic scale of 148 ± 3 Mpc in the fluctuations of the cosmic diffuse background [WMAP], it is the acoustic peak, and in the large-scale distribution of galaxies at red shifts z ≈ 0.3 as found by the SDSS-I collaboration.


The Sloan Digital Sky Survey (SDSS)

To achieve this last result, the SDSS collaboration carried out a first spectroscopic survey (SDSS-I) on approximately 10% of the sky of 47 000 galaxies called "red light" at z ≈ 0.3 from 2000 to 2005, whose function Spatial Autocorrelation showed the acoustic peak of the baryons.

Le pic acoustique des baryons obtenu dans le survey SDSS-I

The acoustic peak of baryons obtained in the SDSS-I survey

This survey was followed by a second (SDSS-II) from 2005 to 2008, bringing together nearly one million galaxies (and more than 120,000 quasars).

The SDSS-III data acquisition is currently underway since July 2008, following an instrument update (increase in the number of spectrograph fibers, improvement of the sensitivity of the CCD camera), and is to continue until 2014. One of the four SDSS-III scientific projects, called BOSS, aims to constrain black energy by observing acoustic oscillations of baryons.



The main objective of BOSS is to measure the spectrum of 1.5 million red light galaxies up to z = 0.8 on 25% of the sky. This represents a 5-fold increase in volume compared to SDSS-II. In addition, the spectra of 160,000 quasars at 2.3 <z <3 will be recorded on a 10% surface of the sky allowing a measurement of the acoustic oscillations of baryons around z = 2.5 via the study of the Lyman forest -alpha. The constraints expected with SDSS-III on the parameters describing the equation of state of the dark energy are shown in the figure below.


Expected constraints on the equation of state of dark energy with the BOSS survey.


A small team is involved in the preparation and analysis of SDSS-III / BOSS data on these two aspects in collaboration with an IPA team. We work on the development of algorithms to refine the calculation of the autocorrelation function and on the use of large-scale numerical simulations for the study of non-linearities and quasar spectrum analysis.


List of APC staff involved





  • Aoustin Claude
  • Blelly Pierre-Louis


  • Lagoutte Dominique
  • Pinçon Jean-Louis
  • Tagger Michel

APC Paris and DAPNIA-CEA Saclay

  • Bouchez Jacques


  • Rodriguez Jérome



The SDSS3 website: