MegaZ-LRG: a photometric redshift catalogue of one million SDSS luminous red galaxies

Adrian Collister, Ofer Lahav, Chris Blake, Russell Cannon, Scott Croom, Michael Drinkwater, Alastair Edge, Daniel Eisenstein, Jon Loveday, Robert Nichol, Kevin Pimbblet, Robert De Propris, Isaac Roseboom, Nic Ross, Tom Shanks, Donald P. Schneider, David Wake

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Abstract

We describe the construction of MegaZ-LRG, a photometric redshift catalogue of over one million luminous red galaxies (LRGs) in the redshift range 0.4 < z < 0.7 with limiting magnitude i < 20. The catalogue is selected from the imaging data of the Sloan Digital Sky Survey (SDSS) Data Release 4. The 2dF-SDSS LRG and Quasar (2SLAQ) spectroscopic redshift catalogue of 13 000 intermediate-redshift LRGs provides a photometric redshift training set, allowing use of ANNz, a neural network-based photometric-redshift estimator. The rms photometric redshift accuracy obtained for an evaluation set selected from the 2SLAQ sample is σz = 0.049 averaged over all galaxies, and σz = 0.040 for a brighter subsample (i < 19.0). The catalogue is expected to contain ∼5 per cent stellar contamination. The ANNz code is used to compute a refined star/galaxy probability based on a range of photometric parameters; this allows the contamination fraction to be reduced to 2 per cent with negligible loss of genuine galaxies. The MegaZ-LRG catalogue is publicly available on the World Wide Web from http://www.2slaq.info.
Original languageEnglish
Pages (from-to)68-76
JournalMonthly Notices of the Royal Astronomical Society
Volume375
Issue number1
Early online date11 Feb 2007
DOIs
Publication statusPublished - 2007

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