Unveiling the Cosmic Gems Arc at z ∼ 10 with JWST NIRCam

We present recent JWST NIRCam imaging observations of SPT0615-JD (also known as the Cosmic Gems Arc), lensed by the galaxy cluster SPT-CL J0615-5746. The 5 '' long arc is the most highly magnified z > 10 galaxy known. It straddles the lensing critical curve and reveals five star clusters with radii of similar to 1 pc or less. We measure the full arc to have F200W 24.5 AB mag, consisting of two mirror images, each 25.3 AB mag with a median magnification of mu similar to 6 0 - 8 + 17 (delensed 29.7 AB mag, M-UV = -17.8). The galaxy has an extremely strong Lyman break F115W-F200W >3.2 mag (2 sigma lower limit), is undetected in all bluer filters (<2 sigma), and has a very blue continuum slope redward of the break (beta = -2.7 +/- 0.1). This results in a photometric redshift z(phot) = 10.2 +/- 0.2 (95% confidence) with no significant likelihood below z < 9.8. Based on spectral energy distribution fitting to the total photometry, we estimate an intrinsic stellar mass of M-* similar to 2.4-5.6 x 10(7)M(circle dot), young mass-weighted age of similar to 21-79 Myr, low dust content (A(V) < 0.15), and a low metallicity of less than or similar to 1% Z(circle dot). We identify a fainter third counterimage candidate within 2 . '' 2 of the predicted position, lensed to AB mag 28.4 and magnified by mu similar to 2, suggesting the fold arc may only show similar to 60% of the galaxy. SPT0615-JD is a unique laboratory to study star clusters observed within a galaxy just 460 Myr after the Big Bang.