J/ApJ/736/43 Gravitational lensing flexion in A1689 with an AIM (Cain+, 2011)
Measuring gravitational lensing flexion in A1689 using an Analytic Image Model.
Cain B., Schechter P.L., Bautz M.W.
<Astrophys. J., 736, 43 (2011)>
=2011ApJ...736...43C 2011ApJ...736...43C
ADC_Keywords: Clusters, galaxy ; Models ; Gravitational lensing
Keywords: dark matter - galaxies: clusters: general -
galaxies: clusters: individual (A1689) - gravitational lensing: weak
Abstract:
Measuring dark matter substructure within galaxy cluster halos is a
fundamental probe of the ΛCDM model of structure formation.
Gravitational lensing is a technique for measuring the total mass
distribution which is independent of the nature of the gravitating
matter, making it a vital tool for studying these
dark-matter-dominated objects. We present a new method for measuring
weak gravitational lensing flexion fields, the gradients of the
lensing shear field, to measure mass distributions on small angular
scales. While previously published methods for measuring flexion focus
on measuring derived properties of the lensed images, such as shapelet
coefficients or surface brightness moments, our method instead fits a
mass-sheet transformation invariant Analytic Image Model (AIM) to each
galaxy image. This simple parametric model traces the distortion of
lensed image isophotes and constrains the flexion fields. We test the
AIM method using simulated data images with realistic noise and a
variety of unlensed image properties, and show that it successfully
reproduces the input flexion fields. We also apply the AIM method for
flexion measurement to Hubble Space Telescope observations of A1689
and detect mass structure in the cluster using flexion measured with
this method. We also estimate the scatter in the measured flexion
fields due to the unlensed shape of the background galaxies and find
values consistent with previous estimates.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 153 50 Position, fit, and error values for the model
parameters of the 50 objects in the A1689 field
with the best 1-flexion estimates
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See also:
B/hst : HST Archived Exposures Catalog (STScI, 2007)
J/ApJ/723/1678 : LensPerfect A1689 analysis (Coe+, 2010)
J/ApJ/668/643 : Multiply imaged gravitational lens systems (Limousin+, 2007)
J/MNRAS/372/1425 : Gravitational lensing analysis of A1689 (Halkola+, 2006)
J/ApJ/621/53 : Multiple arc systems in A1689 (Broadhurst+, 2005)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Seq [1/50] Object number (<[CSB2011] NN> in Simbad)
4- 5 I2 h RAh Hour of right ascension (J2000)
7- 8 I2 min RAm Minute of right ascension (J2000)
10- 13 F4.1 s RAs Second of right ascension (J2000)
15 A1 --- DE- Sign of declination (J2000)
16 I1 deg DEd Degree of declination (J2000)
18- 19 I2 arcmin DEm Arcminute of declination (J2000)
21- 24 F4.1 arcsec DEs Arcsecond of declination (J2000)
26- 31 F6.3 [s-1] logS0 Log of S0 in units of e-/s (1)
33- 37 F5.3 [s-1] e_logS0 S0 uncertainty
39- 44 F6.3 arcsec tc1 θc1 position angle in the image
plane c1 (1)
46- 50 F5.3 arcsec e_tc1 c1 uncertainty
52- 57 F6.3 arcsec tc2 θc2 position angle in the image
plane c2 (1)
59- 63 F5.3 arcsec e_tc2 c2 uncertainty
65- 69 F5.3 arcsec alpha Image scale (=AB0.5 with A and B: semi-axes;
see equation 11) (1)
71- 75 F5.3 arcsec e_alpha alpha uncertainty
77- 82 F6.3 --- e1 Ellipticity parameter 1 (1)
84- 88 F5.3 --- e_e1 e1 uncertainty
90- 95 F6.3 --- e2 Ellipticity parameter 2 (1)
97-101 F5.3 --- e_e2 e2 uncertainty
103-108 F6.3 arcsec-1 p11 1-flexion parameter 1 ψ11 (2)
110-114 F5.3 arcsec-1 e_p11 p11 uncertainty
116-121 F6.3 arcsec-1 p12 1-flexion parameter 2 ψ12 (2)
123-127 F5.3 arcsec-1 e_p12 p12 uncertainty
129-134 F6.3 arcsec-1 p31 3-flexion parameter 1 ψ31 (2)
136-140 F5.3 arcsec-1 e_p31 p31 uncertainty
142-147 F6.3 arcsec-1 p32 3-flexion parameter 2 ψ32 (2)
149-153 F5.3 arcsec-1 e_p32 p32 uncertainty
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Note (1): With an elliptical Gaussian ansatz for the unlensed image, there are
twelve model parameters: six for the unlensed profile and six for the
lensing transformation. The Gaussian parameters are combined into two
real-valued variables, logS0 and α; and two complex variables,
θc and ε. See section 3.2 for further explanations.
Note (2): See equations 5, 17 and 18 and section 4.2 for further explanations.
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History:
From electronic version of the journal
(End) Emmanuelle Perret [CDS] 11-Dec-2012