Paths to quiescence: gaseous feeding, morphology and star-formation histories of galaxies from the HST+MUSE Ultra Deep Field

We propose an 8 orbit WFC3/UVIS F336W imaging program in the MUSE Ultra Deep Field to obtain a deep view of galaxy star formation histories and morphologies at the peak and decline of cosmic star formation (z<2.5). Our program is made unique by two main factors. First, this proposal is built upon the synergy of two public observational programs in this field, a MUSE survey and the deepest HST grism survey with the WFC3/G141 grism. Second, the choice of the field, which hosts several rich galaxy groups at z=0.7-1.1 and two quasars separated by less than 500 kpc at z=3.2. The quasars act as light beacons to probe the gas in and around the group galaxies, making this field ideal for studies of the interaction of galaxies with their local environment. Taking advantage of the unrivaled HST capabilities in the UV, we aim to observe galaxies transitioning from the star forming main sequence to a passive population. Our goals are twofold. i) We will accurately quantify the recent star formation histories of the galaxies and their dust content, which, when complemented by the gas budget, will unveil the physical processes responsible for the onset of a population of passive objects down to 10^9 Msun in stellar mass. ii) We will study the morphology of the young stellar populations probed by the rest-frame far-UV images, which compared to the morphologies of the bulk of the stellar emission and of the nebular emission maps (from the WFC3/IR program), will yield a resolved view of the quenching events. This proposal enables new science goals in this unique field, greatly increasing its legacy value for the astrophysical community.