Constraining Galactic Structure with the LISA White Dwarf Foreground
  White dwarfs comprise 95% of all stellar remnants, and are thus an excellent
tracer of old stellar populations in the Milky Way. Current and planned
telescopes are not able to directly probe the white dwarf population in its
entirety due to its inherently low luminosity. However, the Galactic population
of double white dwarf binaries gives rise to a millihertz gravitational-wave
foreground detectable by the Laser Interferometer Space Antenna (LISA). Here we
show how characterizing this foreground's angular power spectrum will enable us
to probe the Galactic structure in a novel way and measure the vertical scale
height of the Galaxy's oldest stellar populations. We do this using a binary
population synthesis study that incorporates different Galactic spatial
distributions for the double white dwarf population. We find that the level of
anisotropy in the white dwarf foreground's angular power spectrum is strongly
dependent on the vertical scale height of the population. Finally, we show that
LISA can probe the vertical scale height of the Galactic double white dwarf
population with an accuracy of 50 pc-200pc, depending on angular resolution
limits, using the angular power spectrum of the white dwarf foreground.
