Spatially Offset Active Galactic Nuclei I: Selection and Spectroscopic
  Properties
  We present a sample of 18 optically-selected and X-ray detected spatially
offset active galactic nuclei (AGN) from the Sloan Digital Sky Survey (SDSS).
In 9 systems, the X-ray AGN is spatially offset from the galactic stellar core
that is located within the 3'' diameter SDSS spectroscopic fiber. In 11
systems, the X-ray AGN is spatially offset from a stellar core that is located
outside the fiber, with an overlap of 2. To build the sample, we cross-matched
Type II AGN selected from the SDSS galaxy catalogue with archival Chandra
imaging and employed our custom astrometric and registration procedure. The
projected angular (physical) offsets span a range of 0."6 (0.8 kpc) to 17."4
(19.4 kpc), with a median value of 2."7 (4.6 kpc). The offset nature of an AGN
is an unambiguous signature of a galaxy merger, and these systems can be used
to study the properties of AGN in galaxy mergers without the biases introduced
by morphological merger selection techniques. In this paper (Paper I), we use
our sample to assess the kinematics of AGN photoionized gas in galaxy mergers.
We find that spectroscopic offset AGN selection may be up to 89% incomplete due
to small projected velocity offsets. We also find that the magnitude of the
velocity offsets are generally larger than expected if our spatial selection
introduces a bias toward face-on orbits, suggesting the presence of complex
kinematics in the emission line gas of AGN in galaxy mergers.
