We report the discovery of blue shifted (delta(V) > 200 km/s) mid-infrared
[NeIII] and/or [NeV] emission in 25 out of 82 ULIRGs (30% of our sample). The
incidence of blue shifted [NeV] emission is even higher (59%) among the sources
with a [NeV] detection -- the tell-tale signature of an active galactic nucleus
(AGN). Sixteen ULIRGs in our sample, eleven of which are optically classified
as AGN, have [NeIII] blue shifts above 200 km/s. A comparison of the line
profiles of their 12.81um [NeII], 15.56um [NeIII] and 14.32um [NeV] lines
reveals the ionization of the blue shifted gas to increase with blue shift,
implying decelerating outflows in a stratified medium, photo-ionized by the
AGN. The strong correlation of the line width of the [NeIII] line with the
radio luminosity indicates that interaction of expanding radio jets with the
dense ISM surrounding the AGN may explain the observed neon line kinematics for
the strongest radio sources in this sample.Comment: Accepted for publication by ApJ Letters. 15 pages, 4 figure
