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We present a new method to identify luminous off-nuclear X-ray sources in theoutskirts of galaxies from large public redshift surveys, distinguishing themfrom foreground and background interlopers. Using the 3XMM-DR5 catalog of X-raysources and the SDSS DR12 spectroscopic sample of galaxies, with the help ofthis off-nuclear cross-matching technique, we selected 98 sources with inferredX-ray luminosities in the range $10^{41} < L_{\rm X} < 10^{44}\,{\rmerg\,s}^{-1}$, compatible with hyperluminous X-ray objects (HLX). To validatethe method, we verify that it allowed us to recover known HLX candidates suchas ESO 243$-$49 HLX$-$1 and M82 X$-$1. From a statistical study, weconservatively estimate that up to $71 \pm 11$ of these sources may be fore- orbackground sources, statistically leaving at least 16 that are likely to beHLXs, thus providing support for the existence of the HLX population. Weidentify two good HLX candidates and using other publicly available datasets,in particular the VLA FIRST in radio, UKIDSS in the near-infrared, GALEX in theultra-violet and CFHT Megacam archive in the optical, we present evidence thatthese objects are unlikely to be foreground or background X-ray objects ofconventional types, e.g. active galactic nuclei, BL Lac objects, Galactic X-raybinaries or nearby stars. However, additional dedicated X-ray and opticalobservations are needed to confirm their association with the assumed hostgalaxies and thus secure their HLX classification.

A search for hyperluminous X-ray sources in the XMM-Newton source catalog