JWSTs PEARLS: NIRCam imaging and NIRISS spectroscopy of a star-forming galaxy lensed into a near-Einstein Ring by a massive elliptical galaxy

Abstract

We present the discovery, and initial lensing analysis, of a high-redshift galaxy-galaxy lensing system within the JWSTPEARLS/HST-TREASUREHUNT North Ecliptic Pole Time Domain Field (designated NEPJ172238.9+655143.1). The lensing
geometry shears a ???? = 3.6 ± 0.1 star-forming galaxy into a near-Einstein ring with a radius of 0.
′′92, consisting of 4 primary
images, around a foreground massive elliptical galaxy at ???? = 1.258±0.005. The system is fortuitously located within the NIRISS
F200W footprint of the PEARLS survey, enabling spectroscopic identification of the 8500Å TiO band in the foreground galaxy
and allowing tight constraints to be placed on the redshift of the background galaxy based on its continuum detection and lack
of strong emission lines. We calculate magnification factors of 2.6 < ???? < 8.4 for the four images and a total lensing mass
of (4.08 ± 0.07) × 1011????⊙. SED fitting of the foreground elliptical galaxy within the Einstein radius reveals a stellar mass of
∼ 1.26×1011????⊙, providing a mass/light ratio of 3.24. Employing simple scaling relations and assumptions, an NFW dark matter
halo is found to provide the correct remaining mass within 0.12+0.21
−0.09dex. However, if a bottom-heavy IMF for elliptical galaxies
is employed, stellar mass estimations increase and can account for the majority of the lensing mass (up to ∼83%), reducing
the need for dark matter. This system further demonstrates the new discovery space that the combined wavelength coverage,
sensitivity and resolution of JWST now enables.