We investigate a large sample of massive galaxies at z \sim 1 with combined HST broad-band and grism observations to constrain the star-formation histories of these systems as they transition from a star-forming state to quiescence .
Among our sample of massive ( M _ { * } > 10 ^ { 10 } ~ { } \hbox { $ { M } _ { \odot } $ } { } ) galaxies at 0.7 < z < 1.2 , dust-corrected { H } \alpha and UV star-formation indicators agree with a small dispersion ( \sim 0.2 dex ) for galaxies on the main sequence , but diverge and exhibit substantial scatter ( \sim 0.7 dex ) once they drop significantly below the star-forming main sequence .
Significant { H } \alpha emission is present in galaxies with low dust-corrected UV SFR values as well as galaxies classified as quiescent using the UVJ diagram .
We compare the observed { H } \alpha flux distribution to the expected distribution assuming bursty or smooth star-formation histories , and find that massive galaxies at z \sim 1 are most consistent with a quick , bursty quenching process .
This suggests that mechanisms such as feedback , stochastic gas flows , and minor mergers continue to induce low-level bursty star formation in massive galaxies at moderate redshift , even as they quench .