Star Formation and Its Quenching in Hundreds of Galaxies of the Local Universe: A Polychromatic View

Most galaxies build their stellar mass steadily over a Hubble time, but when the process ends, it generally does so rather quickly. Many mechanisms for the quenching of star-formation have been proposed (AGN feedback, strangulation from shock-heated gas, ram-pressure stripping, morphological transformation) but the relative importance of these processes is unclear. The difficulty in distinguishing between these mechanisms lies, in large part, in that relevant measurements are performed holistically, with little attention to how the event proceeds over the face of a galaxy. This is an important omission, since the various quenching models make different predictions as to the spatial progress and time-scale of the phenomenon. To address this important question properly, we will use reliable, spatially-resolved measures of current and recent star formation, throughout the disks and envelopes of a large set of galaxies. Thus, we will build FUV through mid-IR spectral energy distribution (SED) maps, removing systematic offsets between heterogeneous sets of measurements, and exploiting the ability of NUV-optical photometry to discriminate quiescent galaxies from systems with extremely low specific star-formation rates. We will use age-dependent absorption indices to break a well-known SED degeneracy between age and extinction and intercompare the results of several different star formation rate indicators which probe different time-scales (10, 100, 200 Myr, etc.). What makes this investigation possible is the combination of FUV photometry from GALEX, 3-filter near-UV imaging from Swift/UVOT, integral-field emission-line and absorption-line spectroscopy from SDSS MaNGA, near-IR photometry from 2MASS, and mid-IR data from WISE for a large sample of about 100 galaxies in the local universe. With this data set we will be able to measure how the quenching of star formation proceeds - both spatially and temporally - and identify its driving physical mechanism.