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

Kavli Affiliate: Michael D. Gladders

| First 5 Authors: Maxwell Klein, Keren Sharon, Kate Napier, Michael D. Gladders, Gourav Khullar

| Summary:

We present a strong lensing analysis of COOL J1241+2219, the brightest known
gravitationally lensed galaxy at $z geq 5$, based on new multi-band 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. 2021). 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
cluster mass and lensing magnification. We find that the mass enclosed within
the Einstein radius of the z=1.001 cluster lens is
M(<5.77”)=$1.079^{+0.023}_{-0.007}$, significantly lower than other known
strong lensing clusters at its redshift. The average magnification of the giant
arc is $<mu_{arc}>=76^{+40}_{-20}$, a factor of $2.4^{+1.4}_{-0.7}$ greater
than previously estimated from ground-based data; the flux-weighted average
magnification is $<mu_{arc}>=92^{+37}_{-31}$ We update the current
measurements of the stellar mass and star formation rate (SFR) of the source
for the revised magnification, $log(M_star/M_{odot})=9.7pm0.3$ and ${rm
SFR} = 10.3^{+7.0}_{-4.4}$ $ M_{odot} $yr$^{-1}$. 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.

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