Coverage by the HST pointings of the MAMMOTH protoclusters, BOSS1244 (left) and BOSS1542 (right). In each panel we present our HST WFC3 F160W images. The overlaid circular red regions denote the HAEs. The overlaid circular cyan regions denote HAEs that were spectroscopically confirmed by Shi et al. (2021) and fall within the larger HST footprint (a few lie beyond the coverage region). In the left panel, the galaxies that were spectroscopically confirmed via HST grism observations are overlaid as magenta squares. Similarly, the quiescent galaxies identified by Shi et al. (2024) are shown as blue squares. In BOSS1244 and BOSS1542, the SDSS-identified coeval quasars in each field are shown as purple squares. Some of these quasars were previously identified as HAEs. In BOSS1244 and BOSS1542, the densest regions are found in the lower right quadrant with HST coverage. The total area shown for BOSS1244 and BOSS1542 is ∼12′ × 17′.