ALMA 1.1mm Observations of a Conservative Sample of High Redshift Massive Quiescent Galaxies in SHELA

We present a sample of 30 massive (log$(M_{\ast }\mathrm{/}{M}_{\odot })>11$) $z=3-5$ quiescent galaxies selected from the $\mathit{\text{Spitzer-}}$HETDEX Exploratory Large Area (SHELA) Survey and observed at 1.1mm with Atacama Large Millimeter/submillimeter Array (ALMA) Band 6 observations. These ALMA observations would detect even modest levels of dust-obscured star-formation, on order of $\sim 20M_{\odot }{\text{yr}}^{-1}$ at $z\sim 4$ at a $1\sigma$ level, allowing us to quantify the amount of contamination from dusty star-forming sources in our quiescent sample. Starting with a parent sample of candidate massive quiescent galaxies from the Stevans et al. 2021 v1 SHELA catalog, we use the Bayesian $\text{textsc}Bagpipes$ spectral energy distribution fitting code to derive robust stellar masses ($M_{\ast }$) and star-formation rates (SFRs) for these sources, and select a conservative sample of 36 candidate massive ($M_{\ast }>{10}^{11}{M}_{\odot }$) quiescent galaxies, with specific SFRs at $>2\sigma$ below the star-forming main sequence at $z\sim 4$. Based on ALMA imaging, six of these candidate quiescent galaxies have the presence of significant dust-obscured star-formation, thus were removed from our final sample. This implies a $\sim 17\mathrm{\%}$ contamination rate from dusty star-forming galaxies with our selection criteria using the v1 SHELA catalog. This conservatively-selected quiescent galaxy sample at $z=3-5$ will provide excellent targets for future observations to better constrain how massive galaxies can both grow and shut-down their star-formation in a relatively short time period.