  We analyse a controlled N-body + smoothed particle hydrodynamics simulation
of a growing disc galaxy within a non-growing, live dark halo. The disc is
continuously fed with gas and star particles on near-circular orbits and
develops a bar comparable in size to the one of the Milky Way (MW). We extract
line of sight velocity v_los distributions from the model and compare it to
data recently obtained from the APOGEE survey which show distinct high velocity
features around v_los ~ 200 km/s. With an APOGEE like selection function, but
without any scaling nor adjustment, we find v_los distributions very similar to
those in APOGEE. The stars that make up the high v_los features at positive
longitudes l are preferentially young bar stars (age <~ 2-3 Gyr) which move
away from us along the rear side of the bar. At negative l, we find the
corresponding low v_los feature from stars moving towards us. At l>10 degrees
the highest v_los stars are a mixture of bar and background disc stars which
complicates the interpretation of observations. The main peak in v_los is
dominated by fore- and background stars. At a given time, ~40-50 per cent of
high v_los stars occupy x_1 like orbits, but a significant fraction are on more
complex orbits. The observed feature is likely due to a population of
dynamically cool, young stars formed from gas just outside the bar and
subsequently captured by the growing bar. The high v_los features disappear at
high latitudes |b|>~2 degrees which explains the non-detection of such features
in other surveys.
