Strong-Lensing Analysis of MS 1358.4+6245: New Multiple Images and Implications for the Well-Resolved z=4.92 Galaxy

TL;DR

This study uses strong gravitational lensing to uncover new multiple images in galaxy cluster MS 1358.4+6245, revealing a shallow mass profile and providing a highly magnified, well-resolved view of a distant galaxy at redshift 4.92.

Contribution

It introduces a new lensing model with 19 additional multiply-lensed images, improving mass profile accuracy and source characterization at high redshift.

Findings

Discovered 19 new multiply-lensed images, totaling 23 images used for modeling.

Derived a shallow inner mass profile with a slope of approximately -0.33.

Achieved a high magnification (~100x), enabling detailed imaging of a high-redshift galaxy.

Abstract

We present a strong-lensing analysis of the galaxy cluster MS 1358.4+6245 ($z=0.33$), in deep 6-band ACS/HST imaging. In addition to the well-studied system at $z=4.92$, our modelling method uncovers 19 new multiply-lensed images so that a total of 23 images and their redshifts are used to accurately constrain the inner mass distribution. We derive a relatively shallow inner mass profile, $d\log \Sigma/d\log r\simeq -0.33 \pm0.05$ ($r<200$ kpc), with a much higher magnification than estimated previously by models constrained only by the $z=4.92$ system. Using these many new images we can apply a non-parametric adaptive-grid method, which also yields a shallow mass profile without prior assumptions, strengthening our conclusions. The total magnification of the $z_s=4.92$ galaxy is high, about a $\sim100\times$ over its four images, so that the inferred source size, luminosity and star-formation rate are about $\sim5\times$ smaller than previous estimates, corresponding to a dwarf-sized galaxy of radius $\simeq1$ kpc. A detailed image of the interior morphology of the source is generated with a high effective resolution of only $\simeq$50 pc, thanks to the high magnification and to the declining angular diameter distance above $z\sim1.5$ for the standard cosmology, so that this image apparently represents the best resolved object known at high redshift.