The final SDSS-IV/SPIDERS X-ray point source spectroscopic catalogue
  We look to provide a detailed description of the SPectroscopic IDentification
of ERosita Sources (SPIDERS) survey, an SDSS-IV programme aimed at obtaining
spectroscopic classification and redshift measurements for complete samples of
sufficiently bright X-ray sources. We describe the SPIDERS X-ray Point Source
Spectroscopic Catalogue, considering its store of 11,092 observed spectra drawn
from a parent sample of 14,759 ROSAT and XMM sources over an area of 5,129
deg$^2$ covered in SDSS-IV by the eBOSS survey. This programme represents the
largest systematic spectroscopic observation of an X-ray selected sample. A
total of 10,970 (98.9\%) of the observed objects are classified and 10,849
(97.8\%) have secure redshifts. The majority of the spectra (10,070 objects)
are active galactic nuclei (AGN), 522 are cluster galaxies, and 294 are stars.
The observed AGN redshift distribution is in good agreement with simulations
based on empirical models for AGN activation and duty cycle. Forming composite
spectra of type 1 AGN as a function of the mass and accretion rate of their
black holes reveals systematic differences in the H-beta emission line
profiles. This study paves the way for systematic spectroscopic observations of
sources that are potentially to be discovered in the upcoming eROSITA survey
over a large section of the sky.
