Galaxies lensing quadruply imaged quasars lie close to the centers of their lensing potentials

In modeling the potentials of quadruply lensed quasars, investigators often employ models for the stellar surface brightness profile of the lensing galaxy for the sole purpose of eliminating its contamination of the light from the quasar images and their hosts. When the center of that profile is used, it is usually as a weak prior on the center of the potential. But the central maxima in the light from single lensing galaxies lie closer the centers of the lens potentials than has heretofore been thought. New measurements are presented here of the positions of the compact central regions of lensing galaxies observed with the Hubble Space Telescope. Comparing these with modeled positions for the centers of the lensing potential (constrained only by the positions of the four quasar images) we find agreement consistent with the larger of either our measurement uncertainties or 1% of the radius of the Einstein ring.