SPIDERS: the spectroscopic follow-up of X-ray-selected clusters of galaxies in SDSS-IV

Abstract

SPIDERS (The SPectroscopic IDentification of eROSITA Sources) is a programme dedicated to the homogeneous and complete spectroscopic follow-up of X-ray active galactic nuclei and galaxy clusters over a large area (∼7500 deg 2 ) of the extragalactic sky. SPIDERS is part of the Sloan Digital Sky Survey (SDSS)-IV project, together with the Extended Baryon Oscillation Spectroscopic Survey and the Time-Domain Spectroscopic Survey. This paper describes the largest project within SPIDERS before the launch of eROSITA: an optical spectroscopic survey of X-ray-selected, massive (∼10 14 -10 15 M ) galaxy clusters discovered in ROSAT and XMMNewton imaging. The immediate aim is to determine precise ( z ∼ 0.001) redshifts for 4000-5000 of these systems out to z ∼ 0.6. The scientific goal of the program is precision cosmology, using clusters as probes of large-scale structure in the expanding Universe. We present the cluster samples, target selection algorithms and observation strategies. We demonstrate the efficiency of selecting targets using a combination of SDSS imaging data, a robust red-sequence finder and a dedicated prioritization scheme. We describe a set of algorithms and workflow developed to collate spectra and assign cluster membership, and to deliver catalogues of spectroscopically confirmed clusters. We discuss the relevance of line-of-sight velocity dispersion estimators for the richer systems. We illustrate our techniques by constructing a catalogue of 230 spectroscopically validated clusters (0.031 < z < 0.658), found in pilot observations. We discuss two potential science applications of the SPIDERS sample: the study of the X-ray luminosity-velocity dispersion (L X -σ ) relation and the building of stacked phase-space diagrams.

Sloan Digital Sky Survey IV: Mapping the Milky Way, Nearby Galaxies, and the Distant Universe

“…We pay particular attention to the new hardware developments of the program, which are primarily related to APOGEE-2S and MaNGA. More detail on all programs, and in particular how each survey's design addresses its high level requirements, is or will be available in existing and upcoming technical papers Morganson et al 2015;Clerc et al 2016;Dawson et al 2016;Dwelly et al 2017, and APOGEE-2 and TDSS papers in preparation).…”

“…When including previous SDSS legacy spectroscopic observations, SPIDERS reaches a median of approximately 10 galaxies per cluster with spectroscopic redshifts. Details of the clusters targeting algorithmsand of the analysis steps are presented in Clerc et al (2016).…”

The 13th Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the SDSS-IV Survey Mapping Nearby Galaxies at Apache Point Observatory

“…The primary targets were defined by two different SDSS-WISE selection algorithms to determine the eBOSS LRG program (Prakash et al 2016) and several optical-IR and variability selections to determine the eBOSS quasar program (Myers et al 2015). Likewise, objects selected from a combination of X-ray and optical imaging were used to determine the final SPIDERS cluster (Clerc et al 2016) and AGN (Dwelly et al 2017) programs, while variability in PanSTARRS imaging was used to determine the final TDSS program (Morganson et al 2015;Ruan et al 2016).…”

“…They enclose information on the X-ray sources, including flux measurements, and a quantitative measure of the reliability of the association to optical and AllWISE data. The SPIDERS Galaxy Cluster target list (Clerc et al 2016) contains 94,883 and 3,839 objects for RASS and XMM, respectively.…”

“…The selection criteria are somewhat different from the final SPIDERS algorithms. Full details are available in Clerc et al (2016) and Dwelly et al (2017). We summarize the SEQUELS SPIDERS data available in DR13 below.…”