Objects at these redshifts can also be found by looking for
objects with very peculiar colors at the red wavelength ... the
so-called "color break
searches", and the Sloan Digital Sky Survey found a number
of very luminous quasars beyond a redshift of 6 (
Fan et al. 2004).
The figure
shows the highest redshift of these quasars at 6.39.
This spectrum is a high resolution (R=5000) very deep exposure taken
with the ESI spectrograph on the Keck 10m telescope by
Songaila 2004. Note the enormous drop in the flux of the spectrum just
below 0.9 microns which is caused by the obscuration of the intergalactic
gas.
