Baryon Oscillation Spectroscopic Survey – BOSS

The expansion of the Universe is accelerating. The first evidence of this came from supernovae measurements in 1998. This acceleration has been attributed to some 'dark energy'. Understanding its nature is a major challenge of cosmology. We propose to use a baryon acoustic oscillations (BAO) survey to constrain its characteristics. One of the four methods investigated by the US Dark Energy Task Force, BAO has the smallest systematic errors. It is the imprint on matter of primordial baryon-photon fluid oscillations. The corresponding peak in the matter correlation function provides an absolute distance standard (of about 150 Mpc). Baryon oscillations were first detected in 2005 by the SDSS and 2dF surveys, which measured this way the absolute distance scale with 4 % accuracy. The SDSS survey will end in 2008. We propose to use its facility after 2008 to conduct the largest spectroscopic survey to date of cosmological large-scale structure. We will target luminous red galaxies (LRGs) out to z ~ 0.7 over 10,000 square degrees, expanding the SDSS-2 LRG survey by a factor ten. We will also target quasars around z ~ 2.5 to extract from the Lyman-alpha forest the correlation of matter in the range 2 < z < 3, providing another measurement of the baryon oscillations characteristic scale. The goal of the survey is to measure spectra of 1.5 million LRGs and 0.1-0.2 million QSOs. This data will yield absolute distance measurements at the percent level, both transverse (d_A(z)) and along the line of sight (H(z)). The Baryon Oscillation Spectroscopic Survey (BOSS) has been allocated full use of the APO 2.5-m telescope dark time after the end of the SDSS-2 survey. Some hardware upgrades are planned (new CCDs to extend the wavelength coverage and be able to measure LRGs up to z=0.8 and the Lyman-alpha forest down to z=2, new gratings with higher efficiency, new, smaller-core fibers more adapted to the specific targets of the survey and allowing to pack 1000 fibers in the APO spectrographs, from 640 in the original SDSS). Our team has experience in imaging and spectroscopic data reduction, Lyman-alpha forest analysis, numerical simulations and cosmological parameters estimation. We will lead the effort on extracting science from the Lyman-alpha forest data: this is a new method for baryon oscillations studies, which will significantly improve, if successful, the constraints BOSS can put on dark energy. This unprecedented survey will also allow numerous other studies, in the fields of cosmology, large scale structure, massive galaxies, quasars, etc.