A thin slice through the SDSS map of large scale galaxy distribution, showing main sample galaxies (yellow, cyan, green) and LRGs (red).
The Baryon Oscillation Spectroscopic Survey (BOSS) uses spectroscopic redshifts measured with the Apache Point Observatory's 2.5-meter telescope (New Mexico, pictured right) as part of the 2008 through 2014 Sloan Digital Sky Survey III (SDSS3). This telescope has successfully measured redshifts for 930,000 galaxies out to a redshift of z=0.45, although only 15% of the galaxy targets were luminous red galaxies (LRGs) at redshifts of z>0.15, and only 12% were quasars (QSOs) at redshifts of z>2.3, now part of the SDSS Legacy Survey.
The telescope has now been upgraded, increasing the number of fibers per 7 square degree field of view from 640 to 1000, and decreasing the fiber diameters from 3 to 2 arcsec, with an increased wavelength coverage between 3700 and 9800 Angstroms. These improvements have allowed target selection to include 1,500,000 luminous red galaxies out to a redshift of z=0.7, and high redshift quasars between 2.2 < z < 3. BOSS will provide the definitive measurement of the low redshift (z < 0.7) acoustic oscillation scale, reaching close to the cosmic variance limit, and it will pioneer a powerful new method of measuring acoustic oscillations at high redshift, with the QSO analysis yielding separate, 1.5%-precision measurements of the angular diameter distance and the Hubble constant at z=2.5. The BOSS measurements will achieve precise stand-alone constraints on the cosmological expansion rate, the curvature of space, and properties of dark energy, and they will greatly strengthen the overall constraints on evolving dark energy when combined with complementary measurements that use supernovae, weak gravitational lensing, or galaxy clusters. BOSS will also provide rich insights into the matter contents of the Universe, the origin of cosmic structure, and the evolution of galaxies.