A JWST Study of Stellar Clumps lensed by theCluster MACS J0647

Sammanfattning

Stellar clumps dominate the UV-blue morphologies of galaxies at increasing redshifts. Many efforts have been made to understand how such structures form on kpc-scale and to what extent they contribute to the total stellar mass build-up of the galaxy. The superb resolution of the James WebbSpace Telescope (JWST) and its near and mid-infrared (IR) optimized instruments have opened a new window to study young galaxies in their UV/optical rest-frame stellar components. With the additional magnifying effects of gravitational lensing, the stage is set to investigate star formation processes on the smallest physical scales. In this work, we study clumps in a z = 4.8 galaxy lensed by the galaxy cluster MACSJ 0647.7+7015. This galaxy intersects the critical line perpendicularly, giving it a uniquely symmetric appearance. Moreover, its location with respect to the critical line renders it strongly magnified and reveals objects of sizes down to the physical scales expected for star clusters and possibly even smaller. We utilize NIRCam imaging in 6 filters to perform point spread function (PSF) photometry and spectral energy distribution (SED) fitting. Our analyses indicate that we are observing young (< 100 Myr), compact (< 70 pc) star forming regions with masses of 10^6 − 10^8M⊙. We conclude that the most compact of these clumps - with sizes of < 20 pc and possibly as low as < 1 pc - are likely to be young and massive star clusters. Their dynamical ages indicate that they are gravitationally bound, thus stable against expansion and are able to survive over long time scales. From their high surface densities of ∼ 10^4M⊙/pc2, we deduce that they formed in environments much more extreme than observed in the local universe, likely with significantly higher gas densities and SFRs. Not just the star clusters, but also the larger objects exhibit densities comparable with those of local star clusters (> 100M⊙/pc2), indicating that they could be hosting one or multiple of them. These findings emphasize the potential of the JWST to further our understanding of the evolution of star formation on the smallest scales.