Bolocam Observations of Two Unconfirmed Galaxy Cluster Candidates from the Planck Early SZ Sample

TL;DR

This study used Bolocam observations at 140 GHz to confirm one galaxy cluster candidate from the Planck eSZ sample and to analyze another, combining SZ data with WISE infrared observations for validation.

Contribution

First confirmation of a Planck eSZ cluster candidate using Bolocam SZ measurements and infrared data, demonstrating the effectiveness of combined multi-wavelength validation methods.

Findings

Confirmed PLCKESZ G115.71 as a galaxy cluster with high significance.

PLCKESZ G189.84 remains unconfirmed due to lower significance.

Infrared data supported the cluster nature of G115.71 but not G189.84.

Abstract

We present Bolocam observations of two galaxy cluster candidates reported as unconfirmed in the Planck early Sunyaev-Zel'dovich (eSZ) sample, PLCKESZ G115.71+17.52 and PLCKESZ G189.84-37.24. We observed each of these candidates with Bolocam at 140 GHz from the Caltech Submm Observatory in October 2011. The resulting images have white noise levels of ~30 {\mu}KCMB-arcmin in their central regions. We find a significant SZ decrement towards PLCKESZ G115.71. This decrement has a false detection probability of 5.3\times10-5, and we therefore confirm PLCKESZ G115.71 as a cluster. The maximum SZ decrement towards PLCKESZ G189.84 corresponds to a false detection probability of 0.027, and it therefore remains as an unconfirmed cluster candidate. In order to make our SZ-derived results more robust, we have also analyzed data from the Wide-field Infrared Survey Explorer (WISE) at the location of each cluster candidate. We find an overdensity of WISE sources consistent with other clusters in the eSZ at the location of PLCKESZ G115.71, providing further evidence that it is a cluster. We do not find a significant overdensity of WISE sources at the location of PLCKESZ G189.84.