SPIDERS: overview of the X-ray galaxy cluster follow-up and the final spectroscopic data release

TL;DR

SPIDERS is a comprehensive spectroscopic survey of X-ray galaxy clusters, providing high-quality redshifts and a detailed 3D map up to redshift 0.6, enabling cosmological studies and future follow-up prospects.

Contribution

This paper presents the final dataset and analysis of the SPIDERS survey, including its spectroscopic redshifts, cluster catalog, and implications for cosmology, with a focus on its completeness and data quality.

Findings

Achieved over 98% success rate in spectroscopic redshift measurements.

Created a catalog of 2,740 confirmed X-ray galaxy clusters.

Found no evolution in the galaxy cluster X-ray luminosity function up to z=0.6.

Abstract

SPIDERS (The SPectroscopic IDentification of eROSITA Sources) is a large spectroscopic programme for X-ray selected galaxy clusters as part of the Sloan Digital Sky Survey-IV (SDSS-IV). We describe the final dataset in the context of SDSS Data Release 16 (DR16): the survey overall characteristics, final targeting strategies, achieved completeness and spectral quality, with special emphasis on its use as a galaxy cluster sample for cosmology applications. SPIDERS now consists of about 27,000 new optical spectra of galaxies selected within 4,000 photometric red sequences, each associated with an X-ray source. The excellent spectrograph efficiency and a robust analysis pipeline yield a spectroscopic redshift measurement success rate exceeding 98%, with a median velocity accuracy of 20 km s$^{-1}$ (at $z=0.2$). Using the catalogue of 2,740 X-ray galaxy clusters confirmed with DR16 spectroscopy, we reveal the three-dimensional map of the galaxy cluster distribution in the observable Universe up to $z\sim0.6$. We highlight the homogeneity of the member galaxy spectra among distinct regions of the galaxy cluster phase space. Aided by accurate spectroscopic redshifts and by a model of the sample selection effects, we compute the galaxy cluster X-ray luminosity function and we present its lack of evolution up to $z=0.6$. Finally we discuss the prospects of forthcoming large multiplexed spectroscopic programmes dedicated to follow up the next generation of all-sky X-ray source catalogues.