Mass Substructure in Abell 3128

Abstract

We perform a detailed 2-dimensional weak gravitational lensing analysis of the nearby (z = 0.058) galaxy cluster Abell 3128 using deep ugrz imaging from the Dark Energy Camera (DECam). We have designed a pipeline to remove instrumental artifacts from DECam images and stack multiple dithered observations without inducing a spurious ellipticity signal. We develop a new technique to characterize the spatial variation of the PSF which enables us to circularize the field to better than 0.5% and thereby extract the intrinsic galaxy ellipticities. By fitting photometric redshifts to sources in the observation, we are able to select a sample of background galaxies for weak lensing analysis free from low-redshift contaminants. Photometric redshifts are also used to select a high-redshift galaxy subsample with which we successfully isolate the signal from an interloping z = 0.44 cluster. We estimate the total mass of Abell 3128 by fitting the tangential ellipticity of background galaxies with the weak lensing shear profile of an NFW halo, and also perform NFW fits to substructures detected in the 2-D mass maps of the cluster. This study yields one of the highest resolution mass maps of a low-z cluster to date, and is the first step in a larger effort to characterize the redshift evolution of mass substructures in clusters.

17 pages, 15 figures; accepted for publication in ApJ

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