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

T. Dwelly, M. Salvato, A. Merloni, M. Brusa, J. Buchner, S. F. Anderson, Th. Boller, W. N. Brandt, T. Budavári, N. Clerc, A. Del Moro, A. Georgakakis, P. J. Green, C. Jin, M.-l. Menzel, A. D. Myers, K. Nandra, R. C. Nichol, J. Ridl, A. D. SchwopeT. Simm

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SPIDERS (SPectroscopic IDentification of eROSITA Sources) is a Sloan Digital Sky Survey IV (SDSS-IV) survey running in parallel to the Extended Baryon Oscillation Spectroscopic Survey (eBOSS) cosmology project. SPIDERS will obtain optical spectroscopy for large numbers of X-ray-selected active galactic nuclei (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 X-ray selected AGN candidates detected in the ROSAT All Sky and the XMM–Newton Slew surveys. We have exploited a Bayesian cross-matching algorithm, guided by priors based on mid-IR colour–magnitude information from the Wide-field Infrared Survey Explorer 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-localized 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 that have existing optical spectroscopy from SDSS-DR12, including the results of our visual inspections. On completion of the SPIDERS programme, we expect to have collected homogeneous spectroscopic redshift information over a footprint of ∼7500 deg2 for >85 per cent 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.
Original languageEnglish
Pages (from-to)1065-1095
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
Early online date8 Apr 2017
Publication statusPublished - 21 Jul 2017


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