Year: 2012
Type: article
Abstract: Here we present the results of various approaches to measure accurate colours and photometric redshifts (photo-z's) from wide-field imaging data. We use data from the Canada-France-Hawaii-Telescope Legacy Survey (CFHTLS) which have been re- processed by the CFHT Lensing Survey (CFHTLenS) team in order to carry out a number of weak gravitational lensing studies. An emphasis is put on the correction of systematic effects in the photo-z's arising from the different Point Spread Functions (PSF) in the five optical bands. Different ways of correcting these effects are discussed and the resulting photo-z accuracies are quantified by comparing the photo-z's to large spectroscopic redshift (spec-z) data sets. Careful homogenisation of the PSF between bands leads to increased overall accuracy of photo-z's. The gain is particularly pronounced at fainter magnitudes where galaxies are smaller and flux measurements are affected more by PSF-effects. We also study possible re- calibrations of the photometric zeropoints (ZPs) with the help of galaxies with known spec-z's. We find that if PSF-effects are properly taken into account, a re-calibration of the ZPs becomes much less important suggesting that previous such re-calibrations described in the literature could in fact be mostly corrections for PSF-effects rather than corrections for real inaccuracies in the ZPs. The implications of this finding for future surveys like KiDS, DES, LSST, or Euclid are mixed. On the one hand, ZP re-calibrations with spec-z's might not be as accurate as previously thought. On the other hand, careful PSF homogenisation might provide a way out and yield accurate, homogeneous photometry without the need for full spectroscopic coverage. This is the first paper in a series describing the technical aspects of CFHTLenS. (abridged)
Authors: H. Hildebrandt, T. Erben, K. Kuijken, L. van Waerbeke, C. Heymans, J. Coupon, J. Benjamin, C. Bonnett, L. Fu, H. Hoekstra, T. D. Kitching, Y. Mellier, L. Miller, M. Velander, M. J. Hudson, B. T. P. Rowe, T. Schrabback, E. Semboloni, N. Benítez
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funders: National Science Foundation, Smithsonian Institution, European Commission, Deutsche Forschungsgemeinschaft, National Natural Science Foundation of China, Bundesministerium für Bildung und Forschung, Generalitat de Catalunya, Nederlandse Organisatie voor Wetenschappelijk Onderzoek, Shanghai Municipal Education Commission, Centre National de la Recherche Scientifique, Smithsonian Astrophysical Observatory, Natural Sciences and Engineering Research Council of Canada, Science and Technology Facilities Council, Institut national des sciences de l'Univers, FP7 Ideas: European Research Council
Awards: Capitalizing on Gravitational Shear, Gravitational Optics, Dark Matter, and the Evolution of Faint Galaxies, Pan-European training in computational cosmology: modelling cosmic structures, Cosmic Magnification - A New Window to Cosmology, G3827864896, G3857242152, G4088635935, G4511969656, Astrophysics at Oxford: 2010-2015
OpenAlex ID: W1922909567