Strong gravitational lensing analysis of the Cosmic Seahorse observation

Abstract

Abstract: Strong gravitational lensing provides a powerful tool for studying the density profiles of dark matter halos in massive galaxy clusters. In this work, we apply a strong lensing analysis to a recent high-resolution JWST observation of a redshift z = 1.605 galaxy (WISE J122651.0+214958.8, dubbed Cosmic Seahorse). This galaxy is observed in three different images in the sky, two of which form a highly elongated radial arc near the main galaxy of the foreground galaxy cluster (SDSS J1226+2149). After observing an Einstein radius of θE = 20.4′′, we obtain a mass-to-light ratio of Υ ≃ 104Υ⊙ for the main galaxy of the foreground cluster, far beyond the expected values for stellar systems. We numerically show that NFW profiles with parametric exponents for the foreground lensing galaxies are able to reproduce the three observed images. The obtained exponents for the main lensing galaxy are β ≃ 0.7 for the inner region of the mass distribution and γ ≃ 3.4 for the outer one.