A weak lensing mass reconstruction of the largescale filament feeding the massive galaxy cluster MACS J0717.5+3745
Abstract
We report the first weak lensing detection of a largescale filament funnelling matter on to the core of the massive galaxy cluster MACS J0717.5+3745.
Our analysis is based on a mosaic of 18 multipassband images obtained with the Advanced Camera for Surveys aboard the Hubble Space Telescope, covering an area of ̃10 × 20 arcmin^{2}. We use a weak lensing pipeline developed for the Cosmic Evolution Survey, modified for the analysis of galaxy clusters, to produce a weak lensing catalogue. A mass map is then computed by applying a weak gravitational lensing multiscale reconstruction technique designed to describe irregular mass distributions such as the one investigated here. We test the resulting mass map by comparing the mass distribution inferred for the cluster core with the one derived from strong lensing constraints and find excellent agreement.
Our analysis detects the MACS J0717.5+3745 filament within the 3σ detection contour of the lensing mass reconstruction, and underlines the importance of filaments for theoretical and numerical models of the mass distribution in the cosmic web. We measure the filament's projected length as ̃4.5 h741 Mpc, and its mean density as (2.92 ± 0.66) × 10^{8} h_{74} M_{☉} kpc^{2}. Combined with the redshift distribution of galaxies obtained after an extensive spectroscopic followup in the area, we can rule out any projection effect resulting from the chance alignment on the sky of unrelated galaxy groupscale structures. Assuming plausible constraints concerning the structure's geometry based on its galaxy velocity field, we construct a threedimensional (3D) model of the largescale filament. Within this framework, we derive the 3D length of the filament to be 18 h741 Mpc. The filament's deprojected density in terms of the critical density of the Universe is measured as (206 ± 46) ρ_{crit}, a value that lies at the very high end of the range predicted by numerical simulations. Finally, we study the distribution of stellar mass in the field of MACS J0717.5+3749 and, adopting a mean masstolight ratio <M_{*}/L_{K}> of 0.73 ± 0.22 and assuming a Chabrier initial mass function, measure a stellar mass fraction along the filament of (0.9 ± 0.2) per cent, consistent with previous measurements in the vicinity of massive clusters.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 November 2012
 DOI:
 10.1111/j.13652966.2012.21966.x
 arXiv:
 arXiv:1208.4323
 Bibcode:
 2012MNRAS.426.3369J
 Keywords:

 gravitational lensing: weak;
 galaxies: clusters: individual: MACS J0717.5+3745;
 cosmology: observations;
 largescale structure of Universe;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 Accepted for publication in MNRAS