Unveiling the Formation of Massive Galaxies with the James Webb Space Telescope

The formation of massive galaxies, and in particular the quenching of their star formation activity, are among the least understood phases in the history of galaxy evolution. It is widely thought that energetic feedback from Active Galactic Nuclei plays a role in galaxy quenching, but it is not clear how this mechanism actually turns off star formation nor whether additional physical processes, such as gas-rich mergers, are involved. Moreover, it is possible that not all galaxies experience the same type of quenching, since recent studies favor the existence of physically distinct fast and slow quenching channels. Leveraging the groundbreaking observations that will soon be obtained by the James Webb Space Telescope (JWST), I will test the two-channel hypothesis and identify the physical processes responsible for quenching. I am the Principal Investigator of a Cycle-1 JWST program that will obtain spectra with unprecedented depth and wavelength coverage for a representative sample of galaxies at z ~ 2 - 3, a key epoch for quenching. Using this unique spectroscopic data set, in combination with JWST imaging and multi-wavelength follow-up observations, I will: I) derive star formation histories and quenching timescales using advanced spectral fitting techniques; II) characterize the stellar populations, ionized gas, and molecular gas content of galaxies split by quenching timescale, and identify the physical mechanisms involved in fast and slow quenching by comparing these observations to the predictions of theoretical models; III) explore how the quenching processes depend on redshift, mass, and environment using a novel analysis of rest-frame colors measured from large photometric data sets. This project is extremely timely and will take full advantage of the five-year guaranteed lifetime of JWST.