A Test for the Effective Mass-to-Light Ratio in Strong-Lensing Galaxy Clusters
with Adi Zitrin
Abstract/Description: Strong gravitational lensing is a powerful tool for the constraint of total (baryonic and dark) projected mass distributions. In this work, we examine whether the lensing signatures of strongly-lensing galaxy clusters can be well-described by assuming a universal mass-to-light ratio. For that purpose, we formulate a new lensing formalism based on the successful Light-Traces-Mass (LTM) methodology formed by Zitrin and others, replacing two of its principal parameters with physically-motivated ones: DMf , the ratio between dark and baryonic mass; and M/L, the ratio between cluster mass and total luminosity. A set of five intermediate redshift (z ~ 0.4 − 0.8) lensing clusters is analyzed, and the resulting M/L ratios are examined for similarities. Based on the results of these analyses, a basic scheme is proposed for automatically constructing ”blind” galaxy cluster models, i.e. without strong-lensing signatures as input, and its application tested on our dataset. We find our revised LTM method preserves the typical accuracy of previous implementations, with best-fit rms ~ 1” − 2” per image. We find DMf to be hard to constrain in our method, but that a nominal value of 85% dark matter makes for a good fit for all clusters in our dataset. We find the M/L values to be highly dependent on galaxy weights, a secondary parameter of our method meant to compensate for partial luminosity measurement (or missing mass) in the brightest cluster galaxies (BCGs). Setting DMf on a fixed value and applying a fixed weighing scheme for the BCGs, we obtain an average M/L = 21.4 ± 2.1 [M_☉/L_☉], and use it as a nominal value for our automatic modelling scheme. The automatic models, constructed using this nominal mass-to-light value, produce reasonable results, approximately recreating the shapes and sizes of the critical curves of most clusters, with an average deviation of ~ 8.8% in θ_E for all clusters but one. Finally, we identify several future avenues of research for the improvement of our method, most important of which is the correct a priori determination of appropriate BCG weights. Applying our revised method on approximately 30 lensing clusters should overcome the remaining challenges, and allow for automated mass mappings of large samples of clusters, for example, in large sky surveys.