Hubble Frontier Field free-form mass mapping of the massive multiple-merging cluster MACSJ0717.5+3745

Abstract

We examine the latest data on the cluster MACSJ0717.5+3745 from the Hubble Frontier Fields campaign. The critically lensed area is the largest known of any lens and very irregular making it a challenge for parametric modelling. Using our Free-Form method we obtain an accurate solution, identify here many new sets of multiple images, doubling the number of constraints and improving the reconstruction of the dark matter distribution. Our reconstructed mass map shows several distinct central substructures with shallow density profiles, clarifying earlier work and defining well the relation between the dark matter distribution and the luminous and X-ray peaks within the critically lensed region. Using our free-form method, we are able to meaningfully subtract the mass contribution from cluster members to the deflection field to trace the smoothly distributed cluster dark matter distribution. We find 4 distinct concentrations, 3 of which are coincident with the luminous matter. The fourth peak has a significant offset from both the closest luminous and X-ray peaks. These findings, together with dynamical data from the motions of galaxies and gas will be important for uncovering the potentially important implications of this extremely massive and intriguing system.

Strong-lensing analysis of MACS J0717.5+3745 fromHubbleFrontier Fields observations: How well can the mass distribution be constrained?

“…This merged tail corresponds to the counter image of the tail associated with 1.1, for which we measured a spectroscopic of 2.963 (labelled 1.1 * in Limousin et al 2012). In addition, our parametric mass model is not able to reproduce system 30 as proposed by Diego et al (2015b). -system 34: we propose an alternative identification for image 34.1 which significantly improves the rms of this system (1.6 instead of 3.7 when using the identification by Diego et al 2015b).…”

“…powerful gravitational lens, the system has been investigated both in the strong- (Zitrin et al 2009;Limousin et al 2012;Richard et al 2014;Diego et al 2015b) and in the weak-lensing regimes (Jauzac et al 2012;Medezinski et al 2013), further underlining its position as one of the most complex, dynamically active, and massive clusters studied to date.…”

“…The analysis by Diego et al (2015b), using the first third of the data from the HFF observations, identified an additional 17 multiple-image systems, as well as 10 elongated features, assumed to be single images of lensed background galaxies.…”

“…-system 30: we disagree with this identification. Image 30.1 as proposed by Diego et al (2015b) is a faint long arc located between images 1.2 and 1.3. In Limousin et al (2012), we previously interpreted this feature as the merged tail of 1.2 and 1.3.…”

Chandra and JVLA Observations of HST Frontier Fields Cluster MACS J0717.5+3745

“…For one of these subclusters, Ma et al (2009) measured a temperature 5.7 keV temperature, suggesting thatthis component is still at the early stage of merging. Diego et al (2015) found that one of the dark matter components (the one furthest to the northwest) has a significant offset from the closest X-ray peak. Significant offsets between the lensing and X-ray peaks are expected in the case of a high-speed collision in the plane of the sky.…”