J/A+A/585/A84 Shape parameters of lensing galaxies (Biernaux+, 2016)
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 2016A&A...585A..84B (SIMBAD/NED BibCode)
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
(End) Judith Biernaux [ULg] , Patricia Vannier [CDS] 28-Oct-2015