An improved mass reconstruction of Abell 2744 from GLASS and HFF

Abell 2744 is the first cluster for which both the GLASS spectroscopy and the Hubble Frontier Field (HFF) imaging are complete. In Wang et al. (2015), we perform targeted and blind searches of faint emission lines in the GLASS data and thus compile a sample of 55 galaxies with high-confidence spectroscopic redshift, 5 of which are multiply lensed and 3 of which belong to the same system. We also measure photometric redshifts for this sample from the HFF 7-filter exposures. A reasonable agreement between these two sorts of redshift estimation is seen, when nebular emission is considered in photometric redshift fitting.

Modeling gravitational potential of galaxy clusters is known as a notorious difficulty, partly because of the inclusion of mis-identified multiple image systems in lens modeling. In this work, we develop a stringent and rigorous procedure to screen off insecure image systems, based upon colors derived from HFF, image morphology and spectroscopy from GLASS. This leads to a sample of 25/72 multiple arc systems/images as secure out of a total of 57/179 candidate systems/images. The resulting total mass map is only given by the secure set of arcs.

We also derive a stellar mass map from the Spitzer Frontier Field data and find out that the stellar to total mass ratio varies substantially across the cluster field, ranging from 0 to 5%, and the light-traces-mass assumption is not valid in this merging cluster.