Count Your Halos

One of the strongest predictions of the standard cold dark matter paradigm is the hierarchy of structure down to Earth-mass scales.  However, individual self-bound clumps of dark matter--"halos"--are difficult to detect directly.  Instead, we use galaxies as lampposts for halos.  By counting galaxies, we can measure the underlying population of dark matter halos.  In this talk, I describe results that seem completely at odds with each other in measuring the population of small halos.  I argue that the resolution to the problem is a better mapping between galaxies and halos.  I will show what my group is doing so far to address the problem, and what opportunities lie ahead in the wide-field surveys of the 2020's.