COOL-LAMPS. VI. Lens Model and New Constraints on the Properties of COOL J1241+2219, a Bright z = 5 Lyman Break Galaxy and its z = 1 Cluster Lens

Abstract

We present a strong lensing analysis of COOL J1241+2219, the brightest known gravitationally lensed galaxy at z ≥ 5, based on new multiband Hubble Space Telescope (HST) imaging data. The lensed galaxy has a redshift of z = 5.043, placing it shortly after the end of the “Epoch of Reionization,” and an AB magnitude z _AB = 20.47 mag (Khullar et al.). As such, it serves as a touchstone for future research of that epoch. The high spatial resolution of HST reveals internal structure in the giant arc, from which we identify 15 constraints and construct a robust lens model. We use the lens model to extract the cluster mass and lensing magnification. We find that the mass enclosed within the Einstein radius of the z = 1.001 cluster lens is $M(\lt 5\buildrel{\prime\prime}\over{.} \,77)={1.079}_{-0.007}^{+0.023}\times {10}^{13}{M}_{\odot }$ , significantly lower than other known strong lensing clusters at its redshift. The average magnification of the giant arc is 〈 μ _arc 〉 = ${76}_{-20}^{+40}$ , a factor of ${2.4}_{-0.7}^{+1.4}$ greater than previously estimated from ground-based data; the flux-weighted average magnification is 〈 μ _arc 〉 = ${92}_{-31}^{+37}$ . We update the current measurements of the stellar mass and star formation rate (SFR) of the source for the revised magnification to $\mathrm{log}({M}_{\star }/{M}_{\odot })\,=$ 9.7 ± 0.3 and SFR = ${10.3}_{-4.4}^{+7.0}$ M _⊙ yr ^−1 , respectively. The powerful lensing magnification acting upon COOL J1241+2219 resolves the source and enables future studies of the properties of its star formation on a clump-by-clump basis. The lensing analysis presented here will support upcoming multiwavelength characterization with HST and JWST data of the stellar mass assembly and physical properties of this high-redshift lensed galaxy.

Keywords

• Strong gravitational lensing
• Gravitational lensing
• Galaxy clusters
• Galaxy formation