Kavli Affiliate: Paul L. Schechter
| First 5 Authors: Paul L. Schechter, Richard Luhtaru, , ,
| Summary:
When a rectangular hyperbola is constructed from the image positions of a
quadruply lensed quasar, as proposed by Witt (1996), it passes very close to
the the lensing galaxy. The median measured perpendicular offset between the
observed light center of the lens and Witt’s hyperbola is 0.013" for a sample
for 39 systems lensed by a relatively isolated galaxy. The family of lens
models adopted by Witt predicts that the lens lies on the hyperbola, but its
position in not used for its construction. The median offset corresponds to
roughly 1% of the Einstein ring radius, and suggests that the centers of the
lensing potential are close to the light centers of the lens. By putting a
restrictive prior on the perpendicular distance to Witt’s hyperbola (or on the
distance between the galaxy and the potential), one reduces by one the
dimensionality of a model space when fitting data. Taking the brightest pixel
of a lensing galaxy as its center avoids a shortcoming of using the average
light center for a constraint.
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