Sunyaev Zel'dovich Effect Observations of Strong Lensing Galaxy Clusters: Probing the Over-Concentration Problem

TL;DR

This study combines SZ effect measurements and strong lensing data for ten galaxy clusters to investigate their concentration, revealing an over-concentration issue that challenges existing models and may involve systematic effects.

Contribution

It provides new combined SZ and strong lensing analysis for a larger sample, confirming the over-concentration problem in galaxy clusters.

Findings

Einstein radii are twice as large as expected from SZ-inferred masses.

Overconcentration persists in this sample, with a low probability (~3%) of occurring randomly.

Systematic effects like low gas fractions could influence the results.

Abstract

We have measured the Sunyaev Zel'dovich (SZ) effect for a sample of ten strong lensing selected galaxy clusters using the Sunyaev Zel'dovich Array (SZA). The SZA is sensitive to structures on spatial scales of a few arcminutes, while the strong lensing mass modeling constrains the mass at small scales (typically < 30"). Combining the two provides information about the projected concentrations of the strong lensing clusters. The Einstein radii we measure are twice as large as expected given the masses inferred from SZ scaling relations. A Monte Carlo simulation indicates that a sample randomly drawn from the expected distribution would have a larger median Einstein radius than the observed clusters about 3% of the time. The implied overconcentration has been noted in previous studies with smaller samples of lensing clusters. It persists for this sample, with the caveat that this could result from a systematic effect such as if the gas fractions of the strong lensing clusters are substantially below what is expected.