Weak-Lensing Mass Measurements of Five Galaxy Clusters in the South Pole Telescope Survey Using Magellan/Megacam

TL;DR

This study measures galaxy cluster masses via weak lensing using Magellan/Megacam and compares them with SPT SZ and X-ray estimates, finding good agreement and highlighting the potential for improved cosmological constraints.

Contribution

First weak lensing mass measurements of SPT galaxy clusters using Magellan/Megacam, providing a comparison with SZ and X-ray mass estimates and assessing systematic uncertainties.

Findings

Weak lensing masses agree with SZ estimates within uncertainties.

Systematic errors are subdominant to statistical uncertainties.

Sample expansion can improve SPT cluster mass calibration.

Abstract

We use weak gravitational lensing to measure the masses of five galaxy clusters selected from the South Pole Telescope (SPT) survey, with the primary goal of comparing these with the SPT Sunyaev--Zel'dovich (SZ) and X-ray based mass estimates. The clusters span redshifts 0.28 < z < 0.43 and have masses M_500 > 2 x 10^14 h^-1 M_sun, and three of the five clusters were discovered by the SPT survey. We observed the clusters in the g'r'i' passbands with the Megacam imager on the Magellan Clay 6.5m telescope. We measure a mean ratio of weak lensing (WL) aperture masses to inferred aperture masses from the SZ data, both within an aperture of R_500,SZ derived from the SZ mass, of 1.04 +/- 0.18. We measure a mean ratio of spherical WL masses evaluated at R_500,SZ to spherical SZ masses of 1.07 +/- 0.18, and a mean ratio of spherical WL masses evaluated at R_500,WL to spherical SZ masses of 1.10 +/- 0.24. We explore potential sources of systematic error in the mass comparisons and conclude that all are subdominant to the statistical uncertainty, with dominant terms being cluster concentration uncertainty and N-body simulation calibration bias. Expanding the sample of SPT clusters with WL observations has the potential to significantly improve the SPT cluster mass calibration and the resulting cosmological constraints from the SPT cluster survey. These are the first WL detections using Megacam on the Magellan Clay telescope.