In the ROSAT era of the mid-1990's, the problems facing deep X-ray surveys
could be largely solved with 10 m class telescopes. In the first decade of this
new millennium, with X-ray telescopes such as the Chandra X-ray Observatory and
XMM-Newton in operation, deep X-ray surveys are challenging 10 m telescopes.
For example, in the Chandra Deep Field surveys, approximately 30% of the X-ray
sources have optical counterparts fainter than R=25 (I=24).
This paper reviews current progress with 6-10 m class telescopes in following
up sources discovered in deep X-ray surveys, including results from several
X-ray surveys which have depended on telescopes such as Keck, VLT and HET.
Topics include the prospects for detecting extreme redshift (z>6) quasars and
the first detections of normal and starburst galaxies at cosmologically
interesting distances in the X-ray band.
X-ray astronomy can significantly bolster the science case for the next
generation of large aperture (30-100 m) ground-based telescopes and has already
provided targets for these large telescopes through the Chandra and XMM-Newton
surveys. The next generation of X-ray telescopes will continue to challenge
large optical telescopes; this review concludes with a discussion of prospects
from new X-ray missions coming into operation on a 5-30 year timescale.Comment: 15 pages, 6 figures, Invited review for SPIE conference "Science with
6-10 m Class Telescopes