Calibrating the Planck Cluster Mass Scale with Cluster Velocity Dispersions

Abstract

We measure the Planck cluster mass bias using dynamical mass measurements based on velocity dispersions of a subsample of 17 Planck-detected clusters. The velocity dispersions were calculated using redshifts determined from spectra that were obtained at the Gemini observatory with the GMOS multi-object spectrograph. We correct our estimates for effects due to finite aperture, Eddington bias, and correlated scatter between velocity dispersion and the Planck mass proxy. The result for the mass bias parameter, , an error of 17% on the mass bias measurement with 17 clusters. This mass bias value is consistent with most previous weak-lensing determinations. It lies within 1s of the value that is needed to reconcile the Planck cluster counts with the Planck primary cosmic microwave background constraints. We emphasize that uncertainty in the velocity bias severely hampers the precision of the measurements of the mass bias using velocity dispersions. On the other hand, when we fix the Planck mass bias using the constraints from PennaLima et al., based on weak-lensing measurements, we obtain a positive velocity bias of b 0.9 v  at 3s.

Spectroscopic Confirmation and Velocity Dispersions for 20 Planck Galaxy Clusters at 0.16 < z < 0.78

“…We consider it to be a confirmed cluster, and warn the reader about the larger uncertainty (with respect to most of the remaining sample) in the velocity dispersion measurement and its redshift distribution skewness, which both might indicate an unrelaxed dynamical state. We kept this cluster in our sample in Amodeo et al (2017) because, due to the large uncertainty on the velocity dispersion measurement, it does not significantly weight on our final results. PSZ2 G251.13-78.15 was detected by one method with a S N 4.8 (Planck reliability of 90% ), its redshift distribution has a K-S and an S-W probability of 60% and 20% , respectively, to be Gaussian, and an 3% probability of not being a cluster.…”

“…In Figure 2, we show two Gemini/GMOS spectra of galaxies in the cluster PSZ2 G250.04+24.14. The clusters that we followed-up with the Gemini telescopes are listed in Table 2 (see also Table 1 from Amodeo et al 2017). The mass calibration derived from the velocity dispersions of the clusters in this sample is discussed in Amodeo et al (2017), in which we measured the Planck mass bias and constrained the cluster velocity bias.…”

“…XMM-Newton observations (Planck Collaboration et al 2013) reveal two substructures in the X-ray surface brightness, indicating that it is undergoing a merger event (see also van Weeren et al 2014;Mroczkowski et al 2015). Because of the undergoing merger, we have excluded this cluster from the analysis of the velocity dispersion-mass relation in Amodeo et al (2017).…”

“…Both redshift distributions have a standard deviation of ∼0.08, much wider of what is expected for a cluster of galaxies. This target is not a cluster of galaxies, and we have excluded it from the analysis of the velocity dispersion-mass relation in Amodeo et al (2017).…”

“…In a companion paper (Amodeo et al 2017), we use these observations to estimate the clusters' dynamical masses and calibrate the allimportant relation between the SZ Compton parameter, Y, and mass.…”