Lensing and the Centers of Distant Early‐Type Galaxies

Gravitational lensing provides a unique probe of the inner 10-1000 pc ofdistant galaxies (z=0.2-1). Lens theory predicts that every strong lens systemshould have a faint image near the center of the lens galaxy, which should bevisible in radio lenses but have not been observed. We study these ``core''images using models derived from the stellar distributions in nearby early-typegalaxies. We find that realistic galaxies predict a remarkably wide range ofcore images, with lensing magnifications spanning some six orders of magnitude.More concentrated galaxies produce fainter core images, although not with anysimple, quantitative, model independent relation. Some real galaxies havediffuse cores and predict bright core images (magnification mu>~0.1), but morecommon are galaxies that predict faint core images (mu<~0.001). Thus, stellarmass distributions alone are probably concentrated enough to explain the lackof observed core images, and may require observational sensitivity to improveby an order of magnitude before detections of core images become common.Two-image lenses will tend to have brighter core images than four-image lenses,so they will be the better targets for finding core images and exploiting thesetools for studying the central mass distributions of distant galaxies.Comment: 13 pages, emulateapj; submitted to Ap