HUBBLE SPACE TELESCOPE /ADVANCED CAMERA FOR SURVEYS CONFIRMATION OF THE DARK SUBSTRUCTURE IN A520

• Published in: The Astrophysical journal Vol. 783; no. 2; pp. 1 - 18
• Main Authors: Jee, M J, Hoekstra, H, Mahdavi, A, Babul, A
• Format: Journal Article
• Language: English
• Published: United States 10.03.2014
• Subjects: APERTURES; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; Cameras; Centroids; COMPUTERIZED SIMULATION; COSMOLOGY; CROSS SECTIONS; Dark matter; DENSITY; DETECTION; EMISSION; GALAXY CLUSTERS; GRAVITATIONAL LENSES; HYPOTHESIS; MASS; Mathematical models; RADIATION EFFECTS; SPACE; STAR CLUSTERS; Substructures; Surveys; TELESCOPES; UNIVERSE; VISIBLE RADIATION; X RADIATION; X-RAY GALAXIES
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1088/0004-637X/783/2/78

We present a weak-lensing study of the cluster A520 based on Advanced Camera for Surveys (ACS) data. The excellent data quality provides a mean source density of ~109 arcmin super(-2), which improves both resolution and significance of the mass reconstruction compared to a previous study based on Wide Field Planetary Camera 2 (WFPC2) images. We take care in removing instrumental effects such as the charge trailing due to radiation damage of the detector and the position-dependent point-spread function. This new ACS analysis confirms the previous claims that a substantial amount of dark mass is present between two luminous subclusters where we observe very little light. The centroid of the dark peak in the current ACS analysis is offset to the southwest by ~1' with respect to the centroid from the WFPC2 analysis. Interestingly, this new centroid is in better agreement with the location where the X-ray emission is strongest, and the mass-to-light ratio estimated with this centroid is much higher (813 + or - 78 M sub([middot in circle])/L sub(R) sub([middot in circle])) than the previous value; the aperture mass with the WFPC2 centroid provides a consistent mass. Although we cannot provide a definite explanation for the dark peak, we discuss a revised scenario, wherein dark matter with a more conventional range ([sigma] sub(DM)/m sub(DM) < 1 cm super(2) g super(-1)) of self-interacting cross-section can lead to the detection of this dark substructure. If supported by detailed numerical simulations, this hypothesis opens up the possibility that the A520 system can be used to establish a lower limit of the self-interacting cross-section of dark matter.