Analyzing Baryon Acoustic Oscillations in Sparse Spectroscopic Samples
  via Cross-Correlation with Dense Photometry
  We develop a formalism for measuring the cosmological distance scale from
baryon acoustic oscillations (BAO) using the cross-correlation of a sparse
redshift survey with a denser photometric sample. This reduces the shot noise
that would otherwise affect the auto-correlation of the sparse spectroscopic
map. As a proof of principle, we make the first on-sky application of this
method to a sparse sample defined as the z>0.6 tail of the Sloan Digital Sky
Survey's (SDSS) BOSS/CMASS sample of galaxies and a dense photometric sample
from SDSS DR9. We find a 2.8sigma preference for the BAO peak in the
cross-correlation at an effective z=0.64, from which we measure the angular
diameter distance D_M(z=0.64) = (2418 +/- 73 Mpc) (r_s/r_{s,fid}). Accordingly,
we expect that using this method to combine sparse spectroscopy with the deep,
high quality imaging that is just now becoming available will enable higher
precision BAO measurements than possible with the spectroscopy alone.
