Showing papers by "Warrick J. Couch published in 1994"

HST Observations of Gravitationally Lensed Features in the Rich Cluster Ac114

Abstract: Deep Hubble Space Telescope images of superlative resolution obtained for the distant rich cluster AC114 (z=0.31) reveal a variety of gravitational lensing phenomena for which ground-based spectroscopy is available. We present a luminous arc which is clearly resolved by HST and appears to be a lensed z=0.64 sub-L star spiral galaxy with a detected rotation curve. Of greatest interest is a remarkably symmetrical pair of compact blue images separated by 10 arcsec and lying close to the cluster cD. We propose that these images arise from a single very faint background source gravitationally lensed by the cluster core. Deep ground-based spectroscopy confirms the lensing hypothesis and suggests the source is a compact star forming system at a redshift z=1.86. Taking advantage of the resolved structure around each image and their very blue colours, we have identified a candidate third image of the same source roughly 50 arcsec away. The angular separation of the three images is much larger than previous multiply-imaged systems and indicates a deep gravitational potential in the cluster centre. Resolved multiply-imaged systems, readily recognised with HST, promise to provide unique constraints on the mass distribution in the cores of intermediate redshift clusters.

A search for large low-surface brightness galaxies in deep CCD data

Abstract: In this paper, we describe a search for very low-surface-brightness features in deep CCD frames. We show how cross-correlation with templates can be used to detect low-surface-brightness features, which would not be detected using more typical connected-pixel algorithms. The search technique is specifically designed to search for large, low-surface- brightness galaxies like Malin 1. Although we identify 19 potentially interesting, extended, low-surface-brightness objects, we conclude that Malin 1 type objects per se are less prolific than `normal' L^*^ galaxies, and that galaxies with -22 < M_v_ < 19 and μ_0_ ~26 Vmu are at least an order of magnitude less common than their normal-surface- brightness counterparts.