Calibrating photometric redshifts of luminous red galaxies

Nikhil Padmanabhan, Tamas Budavari, David J. Schlegel, Terry Bridges, Jonathan Brinkmann, Russell Cannon, Andrew J. Connolly, Scott M. Croom, Istvan Csabai, Michael Drinkwater, Daniel J. Eisenstein, Paul C. Hewett, Jon Loveday, Bob Nichol, Kevin A. Pimbblet, Roberto De Propis, Donald P. Schneider, Ryan Scranton, Uros Seljak, Tom ShanksIstvan Szapudi, Alexander S. Szalay, David Wake

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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, and (iii) 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 (Two Degree Field) spectroscopic surveys, we find that the photometric redshift accuracy is σ∼ 0.03 for redshifts less than 0.55 and worsens at higher redshift (∼ 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 zero-points. 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 that we develop are applicable to general photometric redshift surveys
Original languageEnglish
Pages (from-to)237-250
Number of pages14
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
Publication statusPublished - 2005


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