Galaxies in the Twilight Zone
by Aaron Romanowsky, San Jose State University
Decades after luminous galaxies were found to be embedded in halos of dark matter (DM),
there are still mysteries about the nature of DM, and how galaxies form and evolve
within DM halos. One of the keys to unlocking these mysteries is the realm of low
surface brightness (LSB) galaxies — in the twilight zone between dark and light.
While enormous efforts are underway to map out faint satellite galaxies in the Local Group,
more general clues can be obtained by extending the search to more distant galaxies —
covering a full range of galaxy type, mass, and environment. I will present results from
several surveys for LSB satellites and streams beyond the Local Group, including
chemodynamical follow-up observations and modeling, and the “discovery” of a new galaxy type:
the ultra-diffuse or “ghost” galaxies.