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A. Knudson, K. U. Ratnatunga, R. E. Griffiths (Carnegie Mellon U.)
We have previously reported the discovery of strong gravitational lensing by faint elliptical galaxies using the WFPC2 on HST (quadruple images, tight arcs, etc.), and here we try to use them to put constraints on lens models. We compare various ellipsoidal surface mass distibutions including those both with and without a core radius as well as models with the mass distributions assumed to have the same axis ratio as the galaxy light. We also look at models which use a spherical mass distibution with a shear term with profiles both empirical and as predicted by CDM simulations. The model parameters and associated errors have been derived by 2-dimensional analysis of the observed HST WFPC2 images. The maximum likelihood procedure iteratively converges simultaneously on the model for the lensing elliptical galaxy and the source of the lensed components. We also compute caustics for each lens and mass model allowing us to determine a discovery cross sections for the lenses in our survey. We find that despite the fact that the lenses are fit equally well with several of the mass models, these models often have different cross sections. These differences could lead to errors when attempting to estimate cosmological constants with gravitational lenses. An understanding of this range of possible mass distributions for the lens galaxy will, in turn, lead to a better undestanding of the cosmic scatter in the parameter estimates and the corresponding errors in the constraints on the fundamental cosmological constants.
The author(s) of this abstract have provided an email address for comments about the abstract: knudson@astro.phys.cmu.edu