J/A+A/585/A84       Shape parameters of lensing galaxies       (Biernaux+, 2016)
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Analysis of luminosity distributions and shape parameters of
strong gravitational lensing elliptical galaxies.
    Biernaux J., Magain P., Sluse D., Chantry V.
    <Astron. Astrophys. 585, A84 (2016)>
    =2016A&A...585A..84B        (SIMBAD/NED BibCode)
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ADC_Keywords: Gravitational lensing ; Galaxies, optical ; Morphology
Keywords: galaxies: elliptical and lenticular, cD -
          galaxies: luminosity function, mass function -
          gravitational lensing: strong

Abstract:
    The luminosity profiles of galaxies acting as strong gravitational
    lenses can be tricky to study. Indeed, strong gravitational lensing
    images display several lensed components, both point-like and diffuse,
    around the lensing galaxy. Those objects limit the study of the galaxy
    luminosity to its inner parts. Therefore, the usual fitting methods
    perform rather badly on such images. Previous studies of strong lenses
    luminosity profiles using software such as like GALFIT or IMFITFITS
    and various PSF-determining methods have resulted in somewhat
    discrepant results.

    The present work aims at investigating the causes of those
    discrepancies, as well as at designing more robust techniques for
    studying the morphology of early-type lensing galaxies with the
    ability to subtract a lensed signal from their luminosity profiles.

    The morphology of early-type lensing galaxies with the ability to
    subtract a lensed signal from their luminosity profiles. Methods. We
    design a new method to independently measure each shape parameter,
    namely, the position angle, ellipticity, and half- light radius of the
    galaxy. Our half-light radius measurement method is based on an
    innovative scheme for computing isophotes that is well suited to
    measuring the morphological properties of gravitational lensing
    galaxies. Its robustness regarding various specific aspects of
    gravitational lensing image processing is analysed and tested against
    GALFIT. It is then applied to a sample of systems from the CASTLES
    database.

Description:
    In the paper we explain procedures designed to measure the position
    angle, the ellipticity and the half-light radius of lensing galaxies,
    that rely on an innovative scheme to compute isophotes. Table 6
    details frame per frame the characteristics of the masks used in this
    work. Those values are in fact the shape parameters of the galaxies,
    before correcting from the effect of the PSF. The relative coordinates
    of the galaxy center, with regards to a reference lensed image, and
    the size of the region of interest are given as well. The reference
    lensed image can be found in Fig. 2 in the paper and is
    the one labelled A (or A1 in some cases).

File Summary:
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 FileName      Lrecl  Records   Explanations
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ReadMe            80        .   This file
table1.dat        78        7   List of the systems that have been processed
                                 in this work
table6.dat        88       41   Characteristics of the masks used
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Byte-by-byte Description of file: table1.dat
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   Bytes Format Units   Label     Explanations
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   1- 13  A13   ---     Name      Name of the system
  15- 16  I2    ---     Nframes   Number of frames
  18- 22  F5.3  ---     Sz        Source redshift
  25- 29  F5.3  ---     Lz        Lens redshift
  31- 32  I2    h       RAh       Right ascension (J2000)
  34- 35  I2    min     RAm       Right ascension (J2000)
  37- 41  F5.2  s       RAs       Right ascension (J2000)
      43  A1    ---     DE-       Declination sign (J2000)
  44- 45  I2    deg     DEd       Declination (J2000)
  47- 48  I2    arcmin  DEm       Declination (J2000)
  50- 53  F4.1  arcsec  DEs       Declination (J2000)
  55- 78  A24   ---     SName     Simbad name
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Byte-by-byte Description of file: table6.dat
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   Bytes Format Units   Label   Explanations
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   1- 13  A13   ---     Name    Name of the system
  17- 26  F10.6 pix     xpos    x-coordinate of the galaxy center (xG - xA)
  29- 38  F10.6 pix     ypos    y-coordinate of the galaxy center (xG - xA)
      41  I1    pix     bmax    Semi-minor axis of the region of interest (1)
  44- 52  A9    ---     Frame   Data frame name in the HST-NICMOS convention
  55- 62  F8.3  deg     PA1     [] Mask position angle (in data frame reference)
  65- 72  F8.3  deg     PA2     [] Mask position angle (North Up, East Right)
  74- 78  F5.2  ---     ell     Mask ellipticity (2)
  81- 88  F8.6  arcsec  reff    PSF-affected half-light radius of the galaxy
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Note (1): i.e. semi-minor axis of the largest isophote computed.
Note (2): Negative ellipticities may occur when the semi-minor and semi-major
           axes have a similar length, and are uneasy to tell apart.
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Acknowledgements:
    Judith Biernaux, jbiernaux(at)ulg.ac.be

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(End)    Judith Biernaux [ULg] , Patricia Vannier [CDS]              28-Oct-2015
