Clustering of photometric luminous red galaxies - II. Cosmological implications from the baryon acoustic scale

A new determination of the sound horizon scale in angular coordinates is presented. It makes use of similar to 0.6 x 106 luminous red galaxies, selected from the Sloan Digital Sky Survey imaging data, with photometric redshifts. The analysis covers a redshift interval that goes from z= 0.5 to 0.6. We find evidence of the baryon acoustic oscillation (BAO) signal at the similar to 2.3s confidence level, with a value of 0BAO(z= 0.55) = (390 +/- 038), including systematic errors. To our understanding, this is the first direct measurement of the angular BAO scale in the galaxy distribution and it is in agreement with previous BAO measurements. We also show how radial determinations of the BAO scale can break the degeneracy in the measurement of cosmological parameters when they are combined with BAO angular measurements. The result is also in good agreement with the 7-year Wilkinson Microscopy Anisotropy Probe (WMAP7) best-fitting cosmology. We obtain a value of w0=-1.03 +/- 0.16 for the equation of state parameter of the dark energy, or OM= 0.26 +/- 0.04 for the matter density, when the other parameters are fixed. We have also tested the sensitivity of current BAO measurements to a time-varying dark energy equation of state, finding wa= 0.06 +/- 0.22 if we fix all the other parameters to the WMAP7 best-fitting cosmology.