RELICS: Strong-lensing analysis of the massive clusters MACS J0308.9+2645 and PLCK G171.9-40.7

TL;DR

This paper presents the first strong lensing analysis of two massive galaxy clusters from the RELICS survey, revealing their large Einstein radii, high magnification areas, and a promising high-redshift galaxy candidate, with models publicly shared.

Contribution

It introduces a new strong lensing analysis of MACS J0308.9+2645 and PLCK G171.9-40.7 using Light-Traces-Mass modeling, providing detailed mass models and magnification maps.

Findings

Both clusters have large Einstein radii (>30") and high magnification areas.

Discovery of a bright, high-redshift (z~6.4) galaxy candidate in MACS J0308.9+2645.

Mass models and magnification maps are publicly available for community use.

Abstract

Strong gravitational lensing by galaxy clusters has become a powerful tool for probing the high-redshift Universe, magnifying distant and faint background galaxies. Reliable strong lensing (SL) models are crucial for determining the intrinsic properties of distant, magnified sources and for constructing their luminosity function. We present here the first SL analysis of MACS J0308.9+2645 and PLCK G171.9-40.7, two massive galaxy clusters imaged with the Hubble Space Telescope in the framework of the Reionization Lensing Cluster Survey (RELICS). We use the Light-Traces-Mass modeling technique to uncover sets of multiply imaged galaxies and constrain the mass distribution of the clusters. Our SL analysis reveals that both clusters have particularly large Einstein radii ($\theta_E>30"$ for a source redshift of $z_s=2$), providing fairly large areas with high magnifications, useful for high-redshift galaxy searches ($\sim2$ arcmin$^{2}$ with $\mu>5$ to $\sim1$ arcmin$^{2}$ with $\mu>10$, similar to a typical \textit{Hubble Frontier Fields} cluster). We also find that MACS J0308.9+2645 hosts a promising, apparently bright (J$\sim23.2-24.6$ AB), multiply imaged high-redshift candidate at $z\sim6.4$. These images are amongst the brightest high-redshift candidates found in RELICS. Our mass models, including magnification maps, are made publicly available for the community through the Mikulski Archive for Space Telescopes.