Mass estimation of the very massive galaxy cluster SRGe CL2305.2$-$2248 from strong lensing

TL;DR

This paper estimates the mass of the high-redshift galaxy cluster SRGe CL2305.2$-$2248 using strong gravitational lensing, revealing discrepancies with other methods possibly due to cluster merging.

Contribution

It presents a novel mass estimation of a very massive, high-redshift galaxy cluster through strong lensing analysis combining optical and archival HST data.

Findings

Mass estimate from strong lensing is 1.5-3 times smaller than X-ray and microwave estimates.

Identification of gravitational lensing features like arcs and arclets in the cluster.

Evidence suggests cluster merging influences mass measurement discrepancies.

Abstract

The galaxy cluster SRGe CL2305.2$-$2248 (SPT-CL J2305$-$2248, ACT-CL J2305.1$-$2248) is one of the most massive clusters at high redshifts ($z \simeq 0.76$) and is of great interest for cosmology. For an optical identification of this cluster, deep images were obtained with the 1.5-m Russian-Turkish telescope RTT-150. Together with the open archival data of the Hubble Space Telescope, it became possible to identify candidates for gravitationally lensed images of distant blue galaxies in the form of arcs and arclets. The observed giant arc near the brightest cluster galaxies allowed us to estimate the radius of the Einstein ring, which is $ 9.8 \pm 1.3 $ arcseconds. The photometric redshift of the lensed source was obtained ($ z_s = 2.44 \pm 0.07 $). Its use in combination with the Einstein radius estimate made it possible to independently estimate the \cl2305 mass. It was done by extrapolating the strong lensing results to large radii and using the model density distribution profiles in relaxed clusters. This extrapolation leads to mass estimates $ \sim 1.5-3 $ times smaller than those obtained from X-ray and microwave observations. A probable cause for this discrepancy may be the process of cluster merging, which is also confirmed by SRGe CL2305.2-2248 morphology in the optical range.