A New Analytic Galactic Luminosity Profile Function
  In 2010 Spergel introduced an alternative to the traditional Sersic form for
galactic luminosity profiles based on modified Bessel functions of the second
kind. His motivation was the desire for an accurate one-parameter profile form
with a simple Fourier transform (in contrast to the Fourier transform of the
Sersic profile which can't be written in closed form), but we have found that
the Spergel profile almost universally makes integrals easier when it replaces
the Sersic profile in the integrand. In the original paper on the subject
Spergel noted that his profile seems to fit galaxies on average just as well as
Sersic's. Here we make this observation quantitative by comparing the residuals
from fitting Sersic and Spergel forms to data. We find that the Spergel profile
actually fits better than the Sersic for a random sample of 16 galaxies.
