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PEARLS: Low Stellar Density Galaxies in the El Gordo Cluster Observed with JWST Published: 3/8/2023 7:15:02 PM Updated: 6/8/2023 9:45:41 PM

Paper abstract: A full understanding of how unusually large "Ultra Diffuse Galaxies" (UDGs)fit into our conventional understanding of dwarf galaxies remains elusive,despite the large number of objects identified locally. A natural extension ofUDG research is the study of similar galaxies at higher redshift to establishhow their properties may evolve over time. However, this has been a challengingtask given how severely systematic effects and cosmological surface brightnessdimming inhibit our ability to study low-surface brightness galaxies athigh-z. Here, we present an identification of low stellar surface densitygalaxies (LDGs), likely the progenitors of local UDGs, at moderate redshiftwith deep near-IR observations of the El Gordo cluster at z = 0.87 with JWST.By stacking 8 NIRCAM filters, we are able to achieve an apparent surfacebrightness sensitivity of 24.59 mag arcsec^{-2}, faint enough to becomplete to the bright end of the LDG population. Our analysis identifiessignificant differences between this population and local UDGs, such as theircolor and size distributions, which suggest that UDG progenitors are bluer andmore extended at high-z than at z = 0. This suggests that multiplemechanisms are responsible for UDG formation and that prolonged transformationof cluster dwarfs is not a primary UDG formation mechanism at high-z.Furthermore, we find a slight overabundance of LDGs in El Gordo, and, incontrast to findings in local clusters, our analysis does not show a deficit ofLDGs in the center of El Gordo, implying that tidal destruction of LDGs issignificant between z = 0.87 and z = 0.