# The Next Generation Virgo Cluster Survey. XX. RedGOLD Background Galaxy Cluster Detections

## TL;DR

This paper presents a new catalog of background galaxy cluster detections from the Next Generation Virgo Cluster Survey using the RedGOLD algorithm, demonstrating high completeness and purity up to redshift 1, and recovering all X-ray clusters with significant mass.

## Contribution

The study introduces a novel cluster detection method applied to NGVS data, achieving high completeness and purity, and effectively detecting clusters up to redshift 1 with fewer bandpasses.

## Key findings

- High completeness (~100%) and purity (~80%) for clusters with M ≥ 10^14 M_sun at z ≤ 0.6.
- Effective cluster detection up to z ~ 1 using four bandpasses despite lower photometric redshift accuracy.
- Recovery of all X-ray clusters with M_500 > 1.4×10^14 M_sun in the surveyed area.

## Abstract

We build a background cluster candidate catalog from the Next Generation Virgo Cluster Survey, using our detection algorithm RedGOLD. The NGVS covers 104$deg^2$ of the Virgo cluster in the $u^*,g,r,i,z$-bandpasses to a depth of $ g \sim 25.7$~mag (5$\sigma$). Part of the survey was not covered or has shallow observations in the $r$--band. We build two cluster catalogs: one using all bandpasses, for the fields with deep $r$--band observations ($\sim 20 \ deg^2$), and the other using four bandpasses ($u^*,g,i,z$) for the entire NGVS area. Based on our previous CFHT-LS W1 studies, we estimate that both of our catalogs are $\sim100\%$($\sim70\%$) complete and $\sim80\%$ pure, at $z\le 0.6$($z\lesssim1$), for galaxy clusters with masses of $M\gtrsim10^{14}\ M_{\odot}$. We show that when using four bandpasses, though the photometric redshift accuracy is lower, RedGOLD detects massive galaxy clusters up to $z\sim 1$ with completeness and purity similar to the five-band case. This is achieved when taking into account the bias in the richness estimation, which is $\sim40\%$ lower at $0.5\le z<0.6$ and $\sim20\%$ higher at $0.6<z< 0.8$, with respect to the five-band case. RedGOLD recovers all the X-ray clusters in the area with mass $M_{500} > 1.4 \times 10^{14} \rm M_{\odot}$ and $0.08<z<0.5$. Because of our different cluster richness limits and the NGVS depth, our catalogs reach to lower masses than the published redMaPPer cluster catalog over the area, and we recover $\sim 90-100\%$ of its detections.