SPIDERS: selection of spectroscopic targets using AGN candidates detected in all-sky X-ray surveys

Abstract

SPIDERS (SPectroscopic IDentification of eROSITA Sources) is an SDSS-IV survey running in parallel to the eBOSS cosmology project. SPIDERS will obtain optical spectroscopy for large numbers of X-ray-selected AGN and galaxy cluster members detected in wide area eROSITA, XMM-Newton and ROSAT surveys. We describe the methods used to choose spectroscopic targets for two sub-programmes of SPIDERS targets: X-ray selected AGN candidates detected in the ROSAT All Sky and the XMMNewton Slew surveys. We have exploited a Bayesian cross-matching algorithm, guided by priors based on mid-IR colour-magnitude information from the WISE survey, to select the most probable optical counterpart to each X-ray detection. We empirically demonstrate the high fidelity of our counterpart selection method using a reference sample of bright well-localised X-ray sources collated from XMM-Newton, Chandra and Swift-XRT serendipitous catalogues, and also by examining blank-sky locations. We describe the down-selection steps which resulted in the final set of SPIDERS-AGN targets put forward for spectroscopy within the eBOSS/TDSS/SPIDERS survey, and present catalogues of these targets. We also present catalogues of ∼12 000 ROSAT and ∼1500 XMM-Newton Slew survey sources which have existing optical spectroscopy from SDSS-DR12, including the results of our visual inspections. On completion of the SPIDERS program, we expect to have collected homogeneous spectroscopic redshift information over a footprint of ∼7500 deg 2 for >85 percent of the ROSAT and XMM-Newton Slew survey sources having optical counterparts in the magnitude range 17<r<22.5, producing a large and highly complete sample of bright X-ray-selected AGN suitable for statistical studies of AGN evolution and clustering.

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).…”

“…The selection of the RASS and XMMSL point sources is limited at r=22 (Galactic extinction corrected). Details of the targeting scheme for Tier 0 AGN will be described in Dwelly et al(2017).…”

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).…”

“…The target catalogs for galaxy clusters and AGNs for SPIDERS from these two satellites have been included in DR13 as value-added catalogs. The SPIDERS AGN target catalogs (Dwelly et al 2017) contain 9,028 candidate targets from RASS and 819 from XMMSL (XMMNewton Slew survey catalog; Saxton et al 2008). 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 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.…”