SPectroscopic IDentifcation of ERosita Sources (SPIDERS)


The main goal of the SPectroscopic IDentfication of ERosita Sources (SPIDERS) survey is to provide a complete and homogeneous optical spectroscopic followup of X-ray sources (both point-like and extended) detected by eROSITA in its first year of survey operation, to begin in Fall 2019. Before then, the SPIDERS Survey will follow-up of the currently existing wide area X-ray surveys. SPIDERS targets all the ROSAT All-Sky Survey (RASS) sources missing spectroscopic follow-up within the SDSS-IV/eBOSS footprint. It targets as well the hard X-ray AGN population detected in the XMM-Newton Slew Survey. A detailed description of the target selection and links to value-added catalogs are available in the SPIDERS target selection page.

SPIDERS clusters of galaxies were selected by cross-correlating faint ROSAT sources with red-galaxy excess found in SDSS imaging in the range 0.1<z<0.6. These are the most massive and largest clusters in the X-ray sky, and represent a well-defined sample that can be used as a first stepping stone for cluster cosmology experiments via measurement of the growth of structure. With ~4,500 X-ray cluster targets, it will be by far the largest homogeneously X-ray selected sample with full spectroscopic followup. Once eROSITA data become available, we will be able to target additional fainter, smaller mass and higher redshift clusters. The better angular resolution of eROSITA over ROSAT, and the better energy resolution, implies we will be able to better characterize the X-ray/optical selection and provide competitive cosmological measurements of cosmic growth.

eBOSS/SPIDERS obtained >30,000 spectra of ROSAT, XMM and eROSITA X-ray selected AGN, about 40% of which in common with eBOSS QSO program and the remaining unique SPIDERS AGN targets. This spectroscopic X-ray selected sample will be ~2.5 times larger than the total number of X-ray AGN with spectroscopic redshift currently known, and about a factor 10 larger than any existing coherent, contiguous, well-defined, X-ray survey.

During its early phases of operations, eROSITA was used to survey a contiguous region of ∼140deg2. This eROSITA Final Equatorial-Depth Survey (eFEDS; Brunner et al. 2021) is intended as an early representative demonstration of the capabilities of the eROSITA all-sky survey, which will not be completed until late 2023. In order to exploit the availability of these X-ray data, we allocated a dedicated set of 12 SDSS-IV/SPIDERS plates to follow up counterparts of eFEDS X-ray sources, to be observed at Apache Point Observatory during the first quarter of 2020. Because of the COVID19-related closure of APO, only 7 of the originally designed plates were observed, most to shallower than expected depth. These special eFEDS plates are released as part of SDSS DR17, and are described in more detail in the DR17 Data Release paper Abdurro’uf et al. (2022). Following the general SPIDERS science goals, both galaxy members of X-ray selected clusters of galaxies and AGN were targeted in these special plates (see SPIDERS target selection page for details).

SPIDERS Technical Details

  • Dark-time observations together with eBOSS
  • July 2014 – February 2019. Final area: 5,300 square degrees
  • ~4,500 red sequence galaxies X-ray clusters
  • ~30,000 X-ray detected AGN and stars
Principal Investigators
Kirpal Nandra, Andrea Merloni (MPE/ Garching bei Muenchen, Germany)
AGN lead scientist
Mara Salvato (MPE)
Clusters lead scientist
Nicolas Clerc (IRAP, France)
Data scientist
Johan Comparat (MPE)

Target selection

The target selection algorithms are described in this page and documented in Clerc et al. 2016 and Dwelly et al. 2017.

The target selection catalogues are available as value added catalogues.

Value added catalogs

Active galactic nuclei

Multi-wavelength properties of XMM-Slew Survey AGN

Multi-wavelength properties of RASS AGN

Optical Emission Line Properties and Black Hole Mass Estimates for SPIDERS DR16 AGN

Galaxy clusters

The SPIDERS-Clusters demonstration sample catalogue

The Brightest Cluster Galaxies properties of SPIDERS X-ray galaxy clusters

SPIDERS X-ray galaxy cluster catalogue for DR16


General papers

  • Merloni et al. 2012, and Predehl et al. 2016 describe the eROSITA mission.
  • Comparat et al. in 2019 describes the DR16 SPIDERS sample.
  • Clerc et al. 2020 describes the DR16 SPIDERS cluster sample.
  • About AGN

  • Dwelly et al. 2017 and Salvato et al. 2018 describe the target selection based on ROSAT and SMM Slew.
  • Coffey et al. 2019 describes the emission line properties and gives black hole estimates.
  • Probing AGN inner structure with X-ray obscured type 1 AGN Liu et al. 2018.
  • X-ray spectral properties of the AGN sample in the northern XMM-XXL field Liu et al. 2016.
  • A spectroscopic survey of X-ray-selected AGNs in the northern XMM-XXL field Menzel et al. 2016.
  • Exploring the Diversity of Type 1 Active Galactic Nuclei Identified in
    SDSS-IV/SPIDERS Wolf et al. 2019.
  • Exploring the halo occupation of AGN using dark-matter cosmological simulations Georgakakis et al. 2019.
  • Active galactic nuclei and their large-scale structure: an eROSITA mock catalogue Comparat et al. 2019.
  • About Clusters

  • SPIDERS: the spectroscopic follow-up of X-ray selected clusters of galaxies in SDSS-IV Clerc et al. 2016.
  • Exploring relations between BCG and cluster properties in the SPectroscopic IDentification of eROSITA Sources survey from 0.05 < z < 0.3 Furnell et al. 2018.
  • Mass calibration of the CODEX cluster sample using SPIDERS spectroscopy - I. The richness-mass relation Capasso et al. 2019.
  • Stellar mass -- halo mass relation for the brightest central galaxies of X-ray clusters since z=0.65 Erfanianfar et al. 2019.
  • Cosmological parameters based on the DR16 SPIDERS clusters sample Ider Chitham et al. 2020
  • Future generations of SPIDERS

  • SDSS-V: Pioneering Panoptic Spectroscopy Kollmeier et al. 2017.
  • 4MOST Consortium Survey 5: Clusters of galaxies Finoguenov et al. 2019.
  • 4MOST Consortium Survey 6: Active Galactic Nuclei Merloni et al. 2019.