JWSTs PEARLS: NIRCam imaging and NIRISS spectroscopy of a $z=3.6$ star-forming galaxy lensed into a near-Einstein Ring by a $z=1.258$ massive elliptical galaxy
Nathan J. Adams, Giovanni Ferrami, Lewi Westcott, Thomas Harvey, Vicente Estrada-Carpenter, Christopher J. Conselice, Duncan Austin, J. Stuart B. Wyithe, Caio M. Goolsby, Qiong Li, Vadim Rusakov, Rogier A. Windhorst, Seth H. Cohen, Rolf A. Jansen, Jake Summers, Roselia O'Brein, Anton M. Koekemoer, Simon P. Driver, Brenda Frye, Nimish P. Hathi, Dan Coe, Norman A. Grogin, Madeline A. Marshall, Nor Pirzkal, Russell E. Ryan, Christopher N. A. Willmer, Haojing Yan, Benne W. Holwerda, Patrick S. Kamieneski, Tom Broadhurst, W. Peter Maksym, Payaswini Saikia, Joseph D. Gelfand
TL;DR
This study reports the discovery and initial analysis of a high-redshift strong galaxy-galaxy lens that produces a near-Einstein ring, lensed by a massive elliptical at $z_l=1.258$ with the background source at $z_s=3.6\pm0.1$. By combining JWST/NIRCam imaging, HST data, and NIRISS F200W spectroscopy, the authors perform light deblending, photometric redshift estimation, and lens modelling (lenstronomy) to derive image magnifications, a total lensing mass of $M_{\mathrm{lensing}}=(4.08\pm0.07)\times10^{11}\,M_\odot$, and a DM mass within the Einstein radius of order $\sim2.8\times10^{11}\,M_\odot$. The background source is inferred to be a moderately dusty starburst with $\log_{10}(M_*/M_\odot)=8.17^{+0.18}_{-0.23}$ and $A_V=0.88^{+0.20}_{-0.13}$, while the foreground lens is a massive, passive elliptical with $\log_{10}(M_*/M_\odot)=11.48^{+0.06}_{-0.15}$ and a potential radio AGN. The work demonstrates JWST’s power to probe mass components and IMF variations in massive ellipticals through lensing at high redshift, and outlines future avenues (e.g., deeper spectroscopy and IFU data) to tighten constraints on dark matter content and stellar mass budgets.
Abstract
We present the discovery, and initial lensing analysis, of a high-redshift galaxy-galaxy lensing system within the JWST-PEARLS/HST-TREASUREHUNT North Ecliptic Pole Time Domain Field (designated NEPJ172238.9+655143.1). The lensing geometry shears a $z=3.6\pm0.1$ star-forming galaxy into a near-Einstein ring with a radius of 0\farcs92, consisting of 4 primary images, around a foreground massive elliptical galaxy at $z=1.258\pm0.005$. The system is fortuitously located within the NIRISS F200W footprint of the PEARLS survey, enabling spectroscopic identification of the 8500A 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 $2.6<μ<8.4$ for the four images and a total lensing mass of $(4.08 \pm 0.07)\times10^{11}M_\odot$. SED fitting of the foreground elliptical galaxy within the Einstein radius reveals a stellar mass of $\sim1.26\times10^{11}M_\odot$, 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 $0.12^{+0.21}_{-0.09}$dex. 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 $\sim$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.