Abstract
Context. The Massive and Distant Clusters of WISE Survey (MaDCoWS) provides a catalog of high-redshift (0.7 ≲ z ≲ 1.5) infrared-selected galaxy clusters. However, the verification of the ionized intracluster medium, indicative of a collapsed and nearly virialized system, is made challenging by the high redshifts of the sample members. Aims. The main goal of this work is to test the capabilities of the Atacama Compact Array (ACA; also known as the Morita Array) Band 3 observations, centered at about 97.5 GHz, to provide robust validation of cluster detections via the thermal Sunyaev–Zeldovich (SZ) effect. Methods. Using a pilot sample that comprises ten MaDCoWS galaxy clusters, accessible to ACA and representative of the median sample richness, we infer the masses of the selected galaxy clusters and respective detection significance by means of a Bayesian analysis of the interferometric data. Results. Our test of the Verification with the ACA – Localization and Cluster Analysis (VACA LoCA) program demonstrates that the ACA can robustly confirm the presence of the virialized intracluster medium in galaxy clusters previously identified in full-sky surveys. In particular, we obtain a significant detection of the SZ effect for seven out of the ten VACA LoCA clusters. We note that this result is independent of the assumed pressure profile. However, the limited angular dynamic range of the ACA in Band 3 alone, short observational integration times, and possible contamination from unresolved sources limit the detailed characterization of the cluster properties and the inference of the cluster masses within scales appropriate for the robust calibration of mass–richness scaling relations.
Highlights
Galaxy cluster richness has long been demonstrated to provide an observationally inexpensive proxy for cluster mass
The results presented in previous Massive and Distant Clusters of WISE Survey (MaDCoWS) papers (Brodwin et al 2015; Decker et al 2019; Gonzalez et al 2019) were derived adopting the universal profile by Arnaud et al (2010) to describe the electron pressure distribution
To get a more immediate handle on the significance of each detection, we report in Table 3 the number of effective standard deviations σeff between the model with and without an SZ component. This can be computed as σeff 2∆ log Z given a log-Bayes factor ∆ log Z = log (Z1/Z0) (Trotta 2008). This differs from the approach taken in the Combined Array for Research in Millimeter-wave Astronomy1 (CARMA) SZ followup papers (Brodwin et al 2015; Gonzalez et al 2015; Decker et al 2019) in that it is more statistically robust, as it properly accounts for the change between different models in the number of parameters and respective priors
Summary
Galaxy cluster richness has long been demonstrated to provide an observationally inexpensive proxy for cluster mass (see, e.g., Rykoff et al 2012; Andreon 2015; Saro et al 2015; Geach & Peacock 2017; Rettura et al 2018; Gonzalez et al 2019). For cluster candidates discovered through optical and infrared selection criteria such as richness, it is essential to verify that the observed galaxy overdensities cannot be ascribed to spurious effects (e.g., lineof-sight projection of galaxies belonging to different haloes). Central to this aim is confirming the presence of a hot X-ray emitting intracluster medium (ICM) heated by gravitational infall and nearly in virial equilibrium. That at z 1 the dimming is expected to weaken due to evolution in the X-ray luminosity for a given mass (Churazov et al 2015)
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