Hubble Space Telescope/Advanced Camera for Surveys Confirmation of the Dark Substructure in A520
Abstract
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-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 ± 78 M ⊙/L R⊙) 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 (σDM/m DM < 1 cm2 g-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.
Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc.- Publication:
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The Astrophysical Journal
- Pub Date:
- March 2014
- DOI:
- 10.1088/0004-637X/783/2/78
- arXiv:
- arXiv:1401.3356
- Bibcode:
- 2014ApJ...783...78J
- Keywords:
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- cosmology: observations;
- dark matter;
- galaxies: clusters: individual: Abell 520;
- gravitational lensing: weak;
- large-scale structure of universe;
- X-rays: galaxies: clusters;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- Accepted to The Astrophysical Journal