X-UDS: The Chandra Legacy Survey of the UKIDSS Ultra Deep Survey Field
  We present the X-UDS survey, a set of wide and deep Chandra observations of
the Subaru-XMM Deep/UKIDSS Ultra Deep Survey (SXDS/UDS) field. The survey
consists of 25 observations that cover a total area of 0.33 deg$^{2}$. The
observations are combined to provide a nominal depth of ~600 ksec in the
central 100 arcmin$^{2}$ region of the field that has been imaged with
Hubble/WFC3 by the CANDELS survey and $\sim$200 ksec in the remainder of the
field. In this paper, we outline the survey's scientific goals, describe our
observing strategy, and detail our data reduction and point source detection
algorithms. Our analysis has resulted in a total of 868 band-merged point
sources detected with a false-positive Poisson probability of
$<1\times10^{-4}$. In addition, we present the results of an X-ray spectral
analysis and provide best-fitting neutral hydrogen column densities, $N_{\rm
H}$, as well as a sample of 51 Compton-thick active galactic nucleus
candidates. Using this sample, we find the intrinsic Compton-thick fraction to
be 30-35% over a wide range in redshift ($z=0.1-3$), suggesting the obscured
fraction does not evolve very strongly with epoch. However, if we assume that
the Compton-thick fraction is dependent on luminosity, as is seen for
Compton-thin sources, then our results are consistent with a rise in the
obscured fraction out to $z\sim3$. Finally, an examination of the host
morphologies of our Compton-thick candidates shows a high fraction of
morphological disturbances, in agreement with our previous results. All data
products described in this paper are made available via a public website.
