Optical-SZE scaling relations for DES optically selected clusters within the SPT-SZ survey

We study the Sunyaev-Zel'dovich effect (SZE) signature in South Pole Telescope (SPT) data for an ensemble of 719 optically identified galaxy clusters selected from 124.6 deg2 of the Dark Energy Survey (DES) science verification data, detecting a stacked SZE signal down to richness λ∼20. The SZE signature is measured using matched-filtered maps of the 2500 deg2 SPT-SZ survey at the positions of the DES clusters, and the degeneracy between SZE observable and matched-filter size is broken by adopting as priors SZE and optical mass-observable relations that are either calibrated using SPT selected clusters or through the Arnaud et al. (2010, A10) X-ray analysis. We measure the SPT signal to noise ζ-λ, relation and two integrated Compton-y Y500-λ relations for the DES-selected clusters and compare these to model expectations accounting for the SZE-optical center offset distribution. For clusters with λ>80, the two SPT calibrated scaling relations are consistent with the measurements, while for the A10-calibrated relation the measured SZE signal is smaller by a factor of 0.61±0.12 compared to the prediction. For clusters at 20<λ<80, the measured SZE signal is smaller by a factor of ∼0.20-0.80 (between 2.3 and 10~σ significance) compared to the prediction, with the SPT calibrated scaling relations and larger λ clusters showing generally better agreement. We quantify the required corrections to achieve consistency, showing that there is a richness dependent bias that can be explained by some combination of contamination of the observables and biases in the estimated masses. We discuss possible physical effects, as contamination from line-of-sight projections or from point sources, larger offsets in the SZE-optical centering or larger scatter in the λ-mass relation at lower richnesses.