Program: GN-2017B-Q-37

In the last decade observations have revealed that quiesent galaxies were much more compact at earlier epochs. Several mechanisms have been proposed to quench star-formation and form these extremely dense spheroids including: (1) compaction via violent disk instabilities or minor merging, (2) gas-rich major mergers, and (3) dissipational collapse formation. Each mechanism would leave characteristic marks on the distribution and motion of stars. However these signatures will disappear with time, age indicators are most sensitive for ~1 Gyr and minor merging will smooth age gradients and diminish rotation. We propose to test these formation models in post-starburst galaxies, which represent the direct, unpolluted products of the quenching process. Although they are extremely rare below z~1, we have leveraged the wide-area of the SDSS spectroscopic survey to identify post-starburst galaxies during the epoch of their decline. Using the GMOS IFU spectrographs we propose to measure spatially resolved stellar populations and kinematics from stellar absorption features for a sample of six of the brightest post-starburst galaxies. We have demonstrated the feasibility of the proposed observations by observing one such galaxy during the Gemini Fast Turnaround cycle and two more in 2017A and are building a census using ALMA of the surprising molecular gas reservoirs of these unique objects. Using the full sample of nine we will constrain the physical mechanisms responsible for forming massive quiescent galaxies.