The Atacama Cosmology Telescope: SZ-based masses and dust emission from
  IR-selected cluster candidates in the SHELA survey
  We examine the stacked thermal Sunyaev-Zel\text{'}dovich (SZ) signals for a
sample of galaxy cluster candidates from the Spitzer-HETDEX Exploratory Large
Area (SHELA) Survey, which are identified in combined optical and infrared
SHELA data using the redMaPPer algorithm. We separate the clusters into three
richness bins, with average photometric redshifts ranging from 0.70 to 0.80.
The richest bin shows a clear temperature decrement at 148 GHz in the Atacama
Cosmology Telescope data, which we attribute to the SZ effect. All richness
bins show an increment at 220 GHz, which we attribute to dust emission from
cluster galaxies. We correct for dust emission using stacked profiles from
Herschel Stripe 82 data, and allow for synchrotron emission using stacked
profiles created by binning source fluxes from NVSS data. We see dust emission
in all three richness bins, but can only confidently detect the SZ decrement in
the highest richness bin, finding $M_{500}$ = $8.7^{+1.7}_{-1.3} \times 10^{13}
M_\odot$. Neglecting the correction for dust depresses the inferred mass by 26
percent, indicating a partial fill-in of the SZ decrement from thermal dust and
synchrotron emission by the cluster member galaxies. We compare our corrected
SZ masses to two redMaPPer mass--richness scaling relations and find that the
SZ mass is lower than predicted by the richness. We discuss possible
explanations for this discrepancy, and note that the SHELA richnesses may
differ from previous richness measurements due to the inclusion of IR data in
redMaPPer.
