  For measurement of the AGN luminosity function and its evolution, X-ray
selection samples all types of AGN and provides reduced obscuration bias in
comparison with UV-excess or optical surveys. The apparent decline in
optically-selected quasars above z~3 may be strongly affected by such a bias.
The Chandra Multiwavelength Project (ChaMP) is characterizing serendipitously
detected X-ray sources in a large number of fields with archival Chandra
imaging. We present a preliminary measure of the co-moving space density using
a sample of 311 AGN found in 23 ChaMP fields (~1.8 deg^2) supplemented with 57
X-ray bright AGN from the CDF-N and CDF-S. Within our X-ray flux (f(0.3-8.0
keV) > 4x10^-15 erg cm^-2 s^-1) and optical magnitude (r' < 22.5) limits, our
sample includes 14 broad emission line AGN at z > 3. Using this X-ray selected
sample, we detect a turnover in the co-moving space density of luminous type 1
AGN (log Lx > 44.5; units erg s^-1; measured in the 0.3-8.0 keV band and
corrected for Galactic absorption) at z > 2.5. Our X-ray sample is the first to
show a behavior similar to the well established evolution of the optical quasar
luminosity function. A larger sample of high redshift AGN and with a greater
fraction of identified sources, either spectroscopic or photometric, at faint
optical magnitudes (r' > 22.5) are required to remove the remaining uncertainty
in our measure of the X-ray luminosity function. We confirm that for z < 1,
lower luminosity AGN (log Lx < 44.5) are more prevalent by more than an order
of magnitude than those with high luminosity. We have combined the Chandra
sample with AGN from the ROSAT surveys to present a measure of the space
density of luminous type 1 AGN in the soft X-ray band (0.5-2.0 keV) which
confirms the broad band turnover described above.
