I think "U" is probably for UNCOVER where that is "Ultradeep Nirspec and nirCam ObserVations before the Epoch of Reionization". https://www.astro.princeton.edu

I think "U" is probably for UNCOVER where that is "Ultradeep Nirspec and nirCam ObserVations before the Epoch of Reionization". https://www.astro.princeton.edu/~goulding/research_uncover.html https://www.astro.princeton.edu/~goulding/research_uncover.h... may have some naming-scheme details I missed glancing through the two papers linked there (and the earlier JWST UNCOVER Treasury Survey <https://arxiv.org/abs/2212.04026 https://arxiv.org/abs/2212.04026>), or someone might eventually be brave and ask him or one of his collaborators directly. :-) I think z ~ 10 is technically an ultra-high redshift galaxy. Table 2 in the "Treasury Survey" above predicts observations of tens of galaxies z > 12, when the universe at large is much more likely to be entirely electrically neutral (~ 10 is in the epoch of reionization, more or less). But please come back with "heroic" spectra from z ~ 15-30 (thinking of the linked article at the top with respect to direct-collapse black holes, Pop III, Lyman-Werner radiation, etc etc), or hey GW spectra from z > 10^10 - 10^30 (beyond scope of topic).