We discuss the construction of a photometric redshift catalogue of Luminous Red Galaxies ( LRGs ) from the Sloan Digital Sky Survey ( SDSS ) , emphasizing the principal steps necessary for constructing such a catalogue – ( i ) photometrically selecting the sample , ( ii ) measuring photometric redshifts and their error distributions , ( iii ) and estimating the true redshift distribution .
We compare two photometric redshift algorithms for these data and find that they give comparable results .
Calibrating against the SDSS and SDSS-2dF spectroscopic surveys , we find that the photometric redshift accuracy is \sigma \sim 0.03 for redshifts less than 0.55 and worsens at higher redshift ( \sim 0.06 for z < 0.7 ) .
These errors are caused by photometric scatter , as well as systematic errors in the templates , filter curves , and photometric zeropoints .
We also parametrize the photometric redshift error distribution with a sum of Gaussians , and use this model to deconvolve the errors from the measured photometric redshift distribution to estimate the true redshift distribution .
We pay special attention to the stability of this deconvolution , regularizing the method with a prior on the smoothness of the true redshift distribution .
The methods we develop are applicable to general photometric redshift surveys .