The X-shaped Bulge of the Milky Way revealed by WISE
  The Milky Way bulge has a boxy/peanut morphology and an X-shaped structure.
This X-shape has been revealed by the `split in the red clump' from star counts
along the line of sight toward the bulge, measured from photometric surveys.
This boxy, X-shaped bulge morphology is not unique to the Milky Way and such
bulges are observed in other barred spiral galaxies. N-body simulations show
that boxy and X-shaped bulges are formed from the disk via dynamical
instabilities. It has also been proposed that the Milky Way bulge is not
X-shaped, but rather, the apparent split in the red clump stars is a
consequence of different stellar populations, in an old classical spheroidal
bulge. We present a WISE image of the Milky Way bulge, produced by downsampling
the publicly available "unWISE" coadds. The WISE image of the Milky Way bulge
shows that the X-shaped nature of the Milky Way bulge is self-evident and
irrefutable. The X-shape morphology of the bulge in itself and the fraction of
bulge stars that comprise orbits within this structure has important
implications for the formation history of the Milky Way, and, given the
ubiquity of boxy X-shaped bulges, spiral galaxies in general.
