  We analyze the density field of 264,283 galaxies observed by the Sloan
Digital Sky Survey (SDSS)-III Baryon Oscillation Spectroscopic Survey (BOSS)
and included in the SDSS data release nine (DR9). In total, the SDSS DR9 BOSS
data includes spectroscopic redshifts for over 400,000 galaxies spread over a
footprint of more than 3,000 deg^2. We measure the power spectrum of these
galaxies with redshifts 0.43 < z < 0.7 in order to constrain the amount of
local non-Gaussianity, f_NL,local, in the primordial density field, paying
particular attention to the impact of systematic uncertainties. The BOSS galaxy
density field is systematically affected by the local stellar density and this
influences the ability to accurately measure f_NL,local. In the absence of any
correction, we find (erroneously) that the probability that f_NL,local is
greater than zero, P(f_NL,local >0), is 99.5%. After quantifying and correcting
for the systematic bias and including the added uncertainty, we find -45 <
f_NL,local < 195 at 95% confidence, and P(f_NL,local >0) = 91.0%. A more
conservative approach assumes that we have only learned the k-dependence of the
systematic bias and allows any amplitude for the systematic correction; we find
that the systematic effect is not fully degenerate with that of f_NL,local, and
we determine that -82 < f_NL,local < 178 (at 95% confidence) and P(f_NL,local
>0) = 68%. This analysis demonstrates the importance of accounting for the
impact of Galactic foregrounds on f_NL,local measurements. We outline the
methods that account for these systematic biases and uncertainties. We expect
our methods to yield robust constraints on f_NL,local for both our own and
future large-scale-structure investigations.
