Exploring effects on magnifications due to line-of-sight galaxies in the Hubble Frontier Fields

Abstract

Cluster lensing has become an important tool in the search for high redshift galaxies through its ability to magnify sources. In order to determine the intrinsic properties of these galaxies, lensing mass models must be constructed to determine the magnification of the images. These models are traditionally two-dimensional, focusing on the mass within the cluster and either ignoring or approximating any contribution from line-of-sight galaxies. In this paper, we present the first full set of three-dimensional mass models of the six Hubble Frontier Fields and use them to test for systematic biases in magnifications due to using the traditional 2D approach. We find that omitting foreground or background galaxies causes image position offsets between 0.1-0.4", a non-negligible fraction of the typical 0.3-0.7" residuals of current state-of-the-art models. We also find that median image magnifications can shift by up to 6%, though it is dependent on the field. This can be alleviated in some cases by approximating the mass in the lensing plane, but a 5% magnification bias still exists in other cases; image position offsets are also improved, but are still present at 0.10".

Further support for a trio of mass-to-light deviations in Abell 370: free-form grale lens inversion using BUFFALO strong lensing data

“…Kawamata et al (2018) used GLAFIC, a parametric method that models the halo components by an NFW profile and cluster member galaxies by a PJ profile. The Keeton group used the parametric LENSMODEL code, which in addition to large-scale haloes for the dark matter and/or hot gas, and small-scale haloes for cluster members, also includes small-scale haloes to model line-of-sight (LoS) galaxies (Raney, Keeton & Brennan 2020a). Among other parametric methods which submitted A370 models using HFF data but do not have a specific publication with their models, are Light Traces Mass (LTM; Zitrin & Broadhurst 2016), and PIEMDeNFW (Zitrin et al 2013), used by the Zitrin group.…”

Pilot-WINGS: An extended MUSE view of the structure of Abell 370

“…A common feature in many of these models is a systematic "external shear" term, needed to properly fit constraints lying at the edge of the multiple-image region (e.g. Strait et al 2018;Kawamata et al 2018;Raney et al 2020). While many physical phenomena can induce such an effect, one common explanation is the presence of additional (unidentified) mass concentrations either within the cluster plane or along the line of sight.…”

Further support for a trio of mass-to-light deviations in Abell 370: free-form Grale lens inversion using BUFFALO strong lensing data

“…Kawamata et al (2018) used , a parametric method which models the halo components by an NFW profile and cluster member galaxies by a pseudo-Jaffe (PJ) profile. The Keeton group used the parametric code, which in addition to large-scale halos for the dark matter and/or hot gas, and small-scale halos for cluster members, also includes small-scale halos to model the line-of-sight (LoS) galaxies (Raney et al 2020a). Among other parametric methods which submitted A370 models with HFF data but do not have a specific publication with their models, are Light Traces Mass (LTM) used in Zitrin & Broadhurst (2016), and PIEMDeNFW (Zitrin et al 2013), used by the Zitrin group.…”