High Confidence Optical Confirmations among the High Signal-to-noise Planck Cluster Candidates
Abstract
We report on newly identified galaxy clusters from the high signal-to-noise (>5σ) end of the second all-sky Planck Sunyaev-Zel’dovich (SZ) catalog (PSZ2). The clusters are identified in deep, optical imaging from the Kitt Peak National Observatory 4 m Mayall telescope taken between 2014 and 2017. Here we focus on the highest richness systems, and identify galaxy clusters through a combination of the maxBCG algorithm and visual image inspection. Galaxy clusters are considered to be confirmed if they are both rich and spatially coincident (≲6‧) with the reported PSZ2 position. Of the 85 fields containing unconfirmed PSZ2 candidates observed, we find 15 (17.6% of the observed sample) corresponding galaxy clusters (0.13 < z < 0.78), 12 of which are previously unrecognized as counterparts. To explain this low identification fraction, we consider three possible scenarios: that clusters are (1) mostly at low-z, (2) mostly at high-z, or (3) located in fields with high object density. None of these scenarios alone can account for the low purity of rich galaxy clusters among the high signal-to-noise PSZ2 unconfirmed candidates.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- February 2019
- DOI:
- 10.3847/1538-4357/aaf3a0
- Bibcode:
- 2019ApJ...871..188B
- Keywords:
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- cosmology: observations;
- galaxies: clusters: general