Dr. David Sand
California Institute of
Technology
Title: A Search For Gravitationally-Lensed Arcs in the HST/WFPC2
Archive
By carefully
examining the images of 129 clusters in the Hubble Space Telescope Wide Field and
Planetary Camera 2 data archive we have located 12 candidate radial arcs and
105 tangential arcs, each of whose length to width ratio exceeds 7. Keck
spectroscopy of candidate radial arcs suggests that contamination of the radial
arc sample from non-lensed objects occurs at about
the 30\% level. With our catalog, we explore the practicality of using the
number ratio of radial to tangential arcs as a statistical measure of the slope
$\beta$ of the dark matter distribution in cluster cores (where $\rho_{DM}\propto
r^{-\beta}$ at small radii). Although the arc statistics presented are
consistent with a range of density profiles -- $\beta<$1.5 depending on
various assumptions, we show that the stellar mass of the brightest cluster
galaxy is the major limitation. With additional data, this method may provide a
reliable statistical constraint on the form of cluster dark matter profiles on
$\lesssim$100 kpc scales.