J/A+A/601/A86 PSF models fits maps (Karabal+, 2017)
A deconvolution technique to correct deep images of galaxies from instrumental
scattered light.
Karabal E., Duc P.-A., Kuntschner H., Chanial P., Cuillandre J.-C., Gwyn S.
<Astron. Astrophys. 601, A86 (2017)>
=2017A&A...601A..86K 2017A&A...601A..86K (SIMBAD/NED BibCode)
ADC_Keywords: Models ; Galaxies, photometry
Keywords: galaxies: evolution - galaxies: elliptical and lenticular, cD -
galaxies: stellar content - galaxies: photometry -
techniques: photometric - techniques: image processing
Abstract:
Deep imaging of the diffuse light that is emitted by stellar fine
structures and outer halos around galaxies is often now used to probe
their past mass assembly. Because the extended halos survive longer
than the relatively fragile tidal features, they trace more ancient
mergers. We use images that reach surface brightness limits as low as
28.5-29mag/arcsec2 (g-band) to obtain light and color profiles up to
5-10 effective radii of a sample of nearby early-type galaxies. These
were acquired with MegaCam as part of the CFHT MATLAS large programme.
These profiles may be compared to those produced using simulations of
galaxy formation and evolution, once corrected for instrumental
effects. Indeed they can be heavily contaminated by the scattered
light caused by internal reflections within the instrument. In
particular, the nucleus of galaxies generates artificial flux in the
outer halo, which has to be precisely subtracted. We present a
deconvolution technique to remove the artificial halos that makes use
of very large kernels. The technique, which is based on PyOperators,
is more time efficient than the model-convolution methods that are
also used for that purpose. This is especially the case for galaxies
with complex structures that are hard to model. Having a good
knowledge of the point spread function (PSF), including its outer
wings, is critical for the method. A database of MegaCam PSF models
corresponding to different seeing conditions and bands was generated
directly from the deep images. We show that the difference in the PSFs
in different bands causes artificial changes in the color profiles, in
particular a reddening of the outskirts of galaxies having a bright
nucleus. The method is validated with a set of simulated images and
applied to three representative test cases: NGC 3599, NGC 3489, and
NGC 4274, which exhibits a prominent ghost halo for two of them. This
method successfully removes this.
Description:
This dataset includes the PSF models that were used to deconvolve the
images and correct them from scattered light. The library includes
PSFs corresponding to different full width at half maximum (FWHM) in g
and r bands. They were built from stacked individual images obtained
with the dithering pattern of the MATLAS large programme. Bright stars
located close to the center of the stacked images were used for the
modeling. The PSFs were normalized to 1, i.e. the pixel with maximum
value in the image is set to 1.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 80 71 List of PSF images
fits/* . 71 Indifidual fits files
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- Nx Number of pixels along X-axis
6- 9 I4 --- Ny Number of pixels along Y-axis
11- 15 I5 Kibyte size Size of FITS file
17 A1 --- Band [rg] Band
19- 22 F4.2 arcsec FWHM FWHM of the PSF
24- 35 A12 --- FileName Name of FITS file, in subdirectory fits (1)
37- 80 A44 --- Title Title of the FITS file
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Note (1): The first character in the file name indicates the band for which
the PSF is built. The numbers after underscores indicate the FWHM of the PSFs
in arcseconds (e.g. r131.fit indicates the PSF with FWHM=1.31 in r band).
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Acknowledgements:
Emin Karabal, karabalemin(at)gmail.com
(End) Patricia Vannier [CDS] 09-Feb-2017