Box/peanut-shaped bulges in action space
  We introduce the study of box/peanut (B/P) bulges in the action space of the
initial axisymmetric system. We explore where populations with different
actions end up once a bar forms and a B/P bulge develops. We find that the
density bimodality due to the B/P bulge (the X-shape) is better traced by
populations with low radial, JR,0, or vertical, Jz,0, actions, or high
azimuthal action, J{\phi},0. Generally populations separated by JR,0 have a
greater variation in bar strength and vertical heating than those separated by
Jz,0. While the bar substantially weakens the initial vertical gradient of
Jz,0, it also drives a strikingly monotonic vertical profile of JR,0. We then
use these results to guide us in assigning metallicity to star particles in a
pure N-body model. Because stellar metallicity in unbarred galaxies depends on
age as well as radial and vertical positions, the initial actions are
particularly well suited for assigning metallicities. We argue that assigning
metallicities based on single actions, or on positions, results in metallicity
distributions inconsistent with those observed in real galaxies. We therefore
use all three actions to assign metallicity to an N-body model by comparing
with the actions of a star-forming, unbarred simulation. The resulting
metallicity distribution is pinched on the vertical axis, has a realistic
vertical gradient and has a stronger X-shape in metal-rich populations, as
found in real galaxies.
