GaaP: PSF- and aperture-matched photometry using shapelets
Abstract
Aims: We describe a new technique for measuring accurate galaxy colours from images taken under different seeing conditions.
Methods: The method involves two ingredients. First we define the Gaussian-aperture-and-PSF flux, which is the Gaussian-weighted flux a galaxy would have if it were observed with a Gaussian PSF. This theoretical aperture flux is independent of the PSF or pixel scale that the galaxy was observed with. Second we develop a procedure for measuring such a “GaaP” flux from observed, pixellated images. This involves modelling source and PSF as a superposition of orthogonal shapelets. A correction scheme is also described that approximately corrects for any residuals to the shapelet expansions.
Results: A series of tests on simulated images shows that it is possible with this method to reduce systematic errors in the matched-aperture fluxes to the level of one percent, which makes it useful for deriving photometric redshifts from large imaging surveys.
- Publication:
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Astronomy and Astrophysics
- Pub Date:
- May 2008
- DOI:
- 10.1051/0004-6361:20066601
- arXiv:
- arXiv:astro-ph/0610606
- Bibcode:
- 2008A&A...482.1053K
- Keywords:
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- techniques: image processing;
- methods: data analysis;
- techniques: photometric;
- galaxies: fundamental parameters;
- Astrophysics
- E-Print:
- 17 pages, A&