CFHTLenS: Improving the quality of photometric redshifts with precision photometry

Details CFHTLenS: Improving the quality of photometric redshifts with precision photometry CFHTLenS: Improving the quality of photometric redshifts with precision photometry

2011-11-18

arxiv.org/abs/1111.4434v2

Astronomy and Astrophysics

Astrophysics

Cosmology and Extragalactic Astrophysics

15 pages, 10 figures, accepted by MNRAS, minor revisions

Scientific paper

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)

Affiliated with

Also associated with

No associations

Rating

CFHTLenS: Improving the quality of photometric redshifts with precision photometry does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with CFHTLenS: Improving the quality of photometric redshifts with precision photometry, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and CFHTLenS: Improving the quality of photometric redshifts with precision photometry will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-549850