SPECTROSCOPIC CONFIRMATION OF TWO MASSIVE RED-SEQUENCE-SELECTED GALAXY CLUSTERS ATz∼ 1.2 IN THE SpARCS-NORTH CLUSTER SURVEY

Abstract

The Spitzer Adaptation of the Red-sequence Cluster Survey (SpARCS) is a deep z ′ -band imaging survey covering the Spitzer SWIRE Legacy fields designed to create the first large homogeneouslyselected sample of massive clusters at z > 1 using an infrared adaptation of the cluster red-sequence method. We present an overview of the northern component of the survey which has been observed with CFHT/MegaCam and covers 28.3 deg 2 . The southern component of the survey was observed with CTIO/MOSAICII, covers 13.6 deg 2 , and is summarized in a companion paper by Wilson et al. (2008). We also present spectroscopic confirmation of two rich cluster candidates at z ∼ 1.2. Based on Nodand-Shuffle spectroscopy from GMOS-N on Gemini there are 17 and 28 confirmed cluster members in SpARCS J163435+402151 and SpARCS J163852+403843 which have spectroscopic redshifts of 1.1798 and 1.1963, respectively. The clusters have velocity dispersions of 490 ± 140 km/s and 650 ± 160 km/s, respectively which imply masses (M 200 ) of (1.0 ± 0.9) x 10 14 M ⊙ and (2.4 ± 1.8) x 10 14 M ⊙ . Confirmation of these candidates as bonaf ide massive clusters demonstrates that two-filter imaging is an effective, yet observationally efficient, method for selecting clusters at z > 1.

Observational probes of cosmic acceleration

“…Today, there are two independent efforts aiming to detect galaxy clusters using IR data: the IRAC Shallow Cluster Survey (ISCS; Eisenhardt et al, 2008) and the Spitzer Adaptation of the Red-Sequence Cluster Survey (SpARCS; Wilson et al, 2006). Both surveys have discovered and spectroscopically confirmed candidate galaxy clusters out to redshift z 1.5 (e.g., Stanford et al, 2005;Brodwin et al, 2006;Eisenhardt et al, 2008;Muzzin et al, 2009;Wilson et al, 2009;Demarco et al, 2010), with some recent detections reaching z 2 Zeimann et al, 2012). Additionally, some of these systems have also been detected in X-rays and/or SZ (Brodwin et al, 2011;Andreon and Moretti, 2011;Brodwin et al, 2012).…”

Evidence for a change in the dominant satellite galaxy quenching mechanism atz = 1

“…GCLASS (Muzzin et al 2012;van der Burg et al 2014) is a sample of 10 galaxy clusters at 0.85 < z < 1.35, selected from the 42 deg 2 SpARCS survey (Muzzin et al 2009;Wilson et al 2009;Demarco et al 2010). SpARCS makes use of deep z-band imaging in the SWIRE (Lonsdale et al 2003) fields to identify overdensities in z − [3.6] colour.…”

The Spitzer Extragalactic Representative Volume Survey (SERVS): Survey Definition and Goals*

“…The Spitzer Adaptation of the Red Sequence Cluster Survey (SpARCS; 58 Muzzin et al 2009Muzzin et al , 2012aWilson et al 2009;DeGroot et al 2012) has imaged the entire SWIRE area (excluding the XMM-LSS field, which is covered by the CFHTLS) in the z 0 filter using MegaCam on the CanadaFrance-Hawaii Telescope or the mosaic camera on the Blanco Telescope at Cerro Tololo Inter-American Observatory (CTIO). The MegaCam observations reach a mean depth of 24.2 AB magnitudes, and the mosaic camera observations reach a mean depth of 24.0 AB magnitudes.…”