Designing an Inflation Galaxy Survey: how to measure $\sigma(f_{\rm NL})
  \sim 1$ using scale-dependent galaxy bias
  The most promising method for measuring primordial non-Gaussianity in the
post-Planck era is to detect large-scale, scale-dependent galaxy bias.
Considering the information in the galaxy power spectrum, we here derive the
properties of a galaxy clustering survey that would optimize constraints on
primordial non-Gaussianity using this technique. Specifically, we ask the
question what survey design is needed to reach a precision $\sigma(f_{\rm
NL}^{\rm loc}) \approx 1$. To answer this question, we calculate the
sensitivity to $f_{\rm NL}^{\rm loc}$ as a function of galaxy number density,
redshift accuracy and sky coverage. We include the multitracer technique, which
helps minimize cosmic variance noise, by considering the possibility of
dividing the galaxy sample into stellar mass bins. We show that the ideal
survey for $f_{\rm NL}^{\rm loc}$ looks very different than most galaxy
redshift surveys scheduled for the near future. Since those are more or less
optimized for measuring the BAO scale, they typically require spectroscopic
redshifts. On the contrary, to optimize the $f_{\rm NL}^{\rm loc}$ measurement,
a deep, wide, multi-band imaging survey is preferred. An uncertainty
$\sigma(f_{\rm NL}^{\rm loc}) = 1$ can be reached with a full-sky survey that
is complete to an $i$-band AB magnitude $i \approx 23$ and has a number density
$\sim 8$ arcmin$^{-2}$. Requirements on the multi-band photometry are set by a
modest photo-$z$ accuracy $\sigma(z)/(1+z) < 0.1$ and the ability to measure
stellar mass with a precision $\sim 0.2$ dex or better (or another proxy for
halo mass with equivalent scatter). While here we focus on the information in
the power spectrum, even stronger constraints can potentially be obtained with
the galaxy bispectrum.
