An Extended Halo-based Group/Cluster finder: application to the DESI legacy imaging surveys DR8

TL;DR

This paper presents an extended halo-based group finder that effectively identifies galaxy groups in the DESI Legacy Surveys DR8, providing a large catalog with accurate group properties for cosmological and galaxy evolution studies.

Contribution

The authors develop and validate a new group finder that uses both photometric and spectroscopic data, improving group detection accuracy and providing a comprehensive galaxy group catalog.

Findings

Successfully identifies over 60% of members in most halos with mass > 10^{12.5} M_sun/h.

Achieves >90% purity for groups with mass > 10^{12} M_sun/h.

Provides a catalog of 5.2 million groups with detailed properties.

Abstract

We extend the halo-based group finder developed by \citet[][]{Yang2005a} to use data {\it simultaneously} with either photometric or spectroscopic redshifts. A mock galaxy redshift survey constructed from a high-resolution N-body simulation is used to evaluate the performance of this extended group finder. For galaxies with magnitude ${\rm z\le 21}$ and redshift $0<z\le 1.0$ in the DESI legacy imaging surveys (the Legacy Surveys), our group finder successfully identifies more than 60\% of the members in about $90\%$ of halos with mass $\ga 10^{12.5}\msunh$. Detected groups with mass $\ga 10^{12.0}\msunh$ have a purity (the fraction of true groups) greater than 90\%. The halo mass assigned to each group has an uncertainty of about 0.2 dex at the high mass end $\ga 10^{13.5}\msunh$ and 0.40 dex at the low mass end. Groups with more than 10 members have a redshift accuracy of $\sim 0.008$. We apply this group finder to the Legacy Surveys DR8 and find 5.2 Million groups with at least 3 members. About 387,000 of these groups have at least 10 members. The resulting catalog containing 3D coordinates, richness, halo masses, and total group luminosities, is made publicly available.