  Recent X-ray surveys have now resolved most of the X-ray background (XRB)
into discrete sources. While this represents a break- through in the
understanding of the XRB, the astrophysical nature of these sources still
remains mysterious. In this article we present a sample of X-ray/optically
selected extragalactic objects which are suitable for adaptive optics
observations in the near infrared (NIR) at highest angu- lar resolution. The
sample is based on a cross-correlation of the Sloan Digital Sky Survey and the
ROSAT All Sky Survey. The NIR properties can help to disentangle the nature of
the X-ray bright, partially absorbed and spectroscopically passive background
objects and their hosts.
