CMB from the SPT-selection. Similarly, we estimate the bias associated with lensed dusty sources to be unimportant for our analysis; their primary impact would be introducing some skewness in the scatter of clusters about our best fit model (Hezaveh et al., 2013).
Emission from cluster galaxies can also potentially bias our measurement. We estimate the effect to be negligible by performing the analysis presented here on subsamples of clusters above differentξ thresholds and by excluding clusters in proximity to known SUMSS sources (Mauch et al., 2003). All subsamples examined provide statistically consistent results. For example, using a subsample of 75 clusters with no associated SUMSS sources brighter than 20 mJy within a projected distance of 3 arcmin from the cluster centers, we obtain consistent results ofα= 0.021+0.042−0.038.
DGE-1144152. Galaxy cluster research at SAO is supported in part by NSF grants AST-1009649 and MRI-0723073. The McGill group acknowledges funding from the National Sciences and Engineering Research Council of Canada, Canada Research Chairs program, and the Cana-dian Institute for Advanced Research.
Chapter 5
Conclusions
In this thesis we reviewed the basic framework of modern cosmology and focused on cosmo-logical studies with galaxy clusters in Chapter 1. Clusters provide rich information about structure formation and are sensitive to the density fluctuations present in the Universe.
Among multiple wavelengths, the microwave techniques developed in recent years provide a unique tool to enhance studies of galaxy clusters. The SZE imprints clusters on the CMB via the interaction between hot Intra-Cluster Medium (ICM) gas and CMB photons. In this thesis we capitalise upon the advantages of the SZE to advance our understanding of the Universe.
5.1 Summary of Results
In Chapter 2 we presented results of a study ofPlanckSZE selected galaxy cluster candidates using Panoramic Survey Telescope & Rapid Response System (Pan-STARRS) imaging data.
To complete the power of SZE surveys for cosmological investigations, the redshifts of clusters are required. In this work we examined 237 Planck galaxy cluster candidates that have no redshift in the Planck source catalogue. Among these cluster candidates, we were able to confirm 60 new galaxy clusters and measure their redshifts. We achieved an photometric redshift accuracy of σz/(1+z) ∼0.022 under a blind analysis of 150 Planck confirmed galaxy clusters with spectroscopic redshifts. For the rest of the candidates, a further 83 candidates were so heavily contaminated by stars due to their locations near the Galactic plane that we were not able to identify optical counterparts. For the remaining 94 candidates we found no counterparts and expect that the majority are noise fluctuations rather than galaxy clusters, given the contamination estimates from thePlanck analysis. Nevertheless, we estimate that about a dozen may be higher redshift clusters for which the Pan-STARRS data are not deep enough to enable optical confirmation. Given the depth of the optical imaging for each candidate together with a model of the expected galaxy population for a massive cluster, we assigned a redshift limit beyond which we would not have expected to detect the cluster with at a minimum of 95 percent confidence.
In Chapter 3 we explored the SZE signature of a sample of 46 X-ray selected groups and clusters within SPT 150 GHz and 95 GHz maps. The X-ray sample drawn from∼6deg2 of the XMM-Newton Blanco Cosmology Survey (XMM-BCS) probes lower X-ray luminosities (∼1042 – 1044 ergs s−1) up to redshift 1.02, making it complementary to previous studies.
Using X-ray luminosity as a mass proxy, we develop and test an analysis tool that extracts selection-bias corrected constraints on the SZE significance- and Y500-mass relations for low mass clusters and groups. The SZE significance-mass relation is in good agreement with an extrapolation of the relation obtained from high mass clusters. However, the fit to the Y500-mass relation at low masses, while in good agreement with the extrapolation from high mass SPT clusters, is in tension at 2.8σ with the constraints from the Planck sample. We examine the tension with thePlanck relation, discussing sample differences and biases that could contribute to the tension. We also present an analysis of the radio galaxy point source population in this ensemble of X-ray selected systems. We find 18 of our systems have 1 GHz SUMSS sources within 2 arcmin of the X-ray centre, and 3 of these are detected also by SPT.
Two of these three SPT point sources are associated with the group BCG, and the third is a quasar candidate. We examine the impact of these point sources on our SZE scaling relation analyses and find no evidence of biases. We also examined the impact of dusty galaxies by stacking the 220 GHz data. We found 2.8σ significant evidence of flux excess, which would correspond to an average underestimate of the SZE signal that is (17±9) % in this sample of low mass systems. Finally, we explore the impact of improved data that will be available from SPTpol and XMM-XXL, showing that it will lead to a factor of four to five tighter constraints on these SZE mass-observable relations.
In Chapter 4 we used clusters as a tool to examine one prediction of standard cosmology:
the adiabatic evolution of the temperature of the CMB blackbody radiation. We used SPT data to study the spectrum of the SZE in a sample of galaxy clusters over a range of redshifts to probe for deviations from the expected adiabatic evolution of the CMB temperature of the formT(z) =T0(1 +z)1−α. We developed a method to constrain the temperature evolution of the CMB by the ratio of the SZE signal measured at 95 and 150 GHz in the SPT data. We verified this approach with mock observations of clusters from a new set of hydrodynamical simulations. We applied this method to a sample of 158 SPT-selected clusters from 720 deg2 spanning a redshift range of 0.05 < z < 1.35. The measured α = 0.017+0.030−0.028, is consistent with the standard model prediction of α = 0. Combining with other published results, we find α = 0.005±0.012, an improvement of ∼ 10% over published constraints. In addition analyses of the combined results provides a strong constraint on the effective equation of state in models of decaying dark energyweff =−0.994±0.010.