Diagnosing, Addressing, and Forecasting CIB Contamination in Spectral Measurements of the Sunyaev Zel dovich Effect

Studies of galaxy clusters are a cornerstone of modern observational cosmology. Clusters not only represent the most massive gravitationally collapsed structures in the universe, but also act as laboratories for the detailed physics of structure formation. A precise understanding of the thermodynamics and structure of the intra-cluster medium (ICM), which behaves as the cluster's atmosphere, can yield crucial insights into the underlying processes that govern how objects form in the universe. The Sunyaev-Zeldovich (SZ) effect, which arises from scattering of cosmic microwave background photons with the ICM, provides a useful diagnostic tool to study galaxy clusters. At the temperatures typical of the ICM, relativistic corrections to this scattering process are important, and are called the relativistic SZ (rSZ) effect. Owing to their different dependencies on ICM density and cluster redshift, rSZ effect observations promise to be an ideal complement to the X-ray observations that have informed much of our current understanding of the ICM. Detecting the rSZ effect requires a precise measurement of the cluster's surface brightness in multiple observing bands spanning sub-mm and mm wavelengths. To date, such rSZbased temperature measurements have been attempted in a handful of galaxy clusters, and in statistical studies of large samples of low-SNR cluster images with Planck. Both targeted and statistical measurements suffer from large uncertainties related to the treatment of a cluster-coincident signal that is consistent with thermal dust emission. The source of this cluster-coincident dust emission, which is not yet known, needs to be characterized in order to advance rSZ studies. In this program, we propose to make a robust and high significance measurement of the rSZ signal in a sample of 56 clusters using sub-mm data from Herschel-SPIRE, and mm data from Planck and Bolocam. As part of this work, we will use the deep high-resolution SPIRE images to completely characterize the source(s) of the cluster-coincident dust emission. The rSZ-derived ICM temperature maps obtained from this analysis will be compared to equivalent temperatures derived from X-ray measurements to demonstrate the validity and utility of the method. We will also perform a full analysis of mock observations of simulated clusters to further vet our analysis pipeline. This program will help develop analysis methods for upcoming rSZ measurements, which promise to become a workhorse for future detailed ICM studies. This work will also help to inform design choices of potential missions capable of rSZ measurements, such as OST and PICO. This program is directly relevant to several of the questions called out in the NASA Physics of the Cosmos (PCOS) and Cosmic Origins (COR) Programs, and achieves the primary goal of the NASA ADAP solicitation by enabling a high-impact science investigation that would not be possible to address through an individual observing program using archival, publicly-available data.