Measuring Baryon Acoustic Oscillations on 21 cm intensity fluctuations
  at moderate redshifts
  After reionization, emission in the 21 cm hyperfine transition provides a
direct probe of neutral hydrogen distributed in galaxies. Different from galaxy
redshift surveys, observation of baryon acoustic oscillations in the cumulative
21 cm emission may offer an attractive method for constraining dark energy
properties at moderate redshifts. Keys to this program are techniques to
extract the faint cosmological signal from various contaminants, such as
detector noise and continuum foregrounds. In this paper, we investigate the
possible systematic and statistical errors in the acoustic scale estimates
using ground-based radio interferometers. Based on the simulated 21 cm
interferometric measurements, we analyze the performance of a Fourier-space,
light-of-sight algorithm in subtracting foregrounds, and further study the
observing strategy as a function of instrumental configurations. Measurement
uncertainties are presented from a suite of simulations with a variety of
parameters, in order to have an estimate of what behaviors will be accessible
in the future generation of hydrogen surveys. We find that 10 separate
interferometers, each of which contains $\sim 300$ dishes, observes an
independent patch of the sky and produces an instantaneous field-of-view of
$\sim 100$ $\rm deg^2$, can be used to make a significant detection of acoustic
features over a period of a few years. Compared to optical surveys, the broad
bandwidth, wide field-of-view and multi-beam observation are all unprecedented
capabilities of low-frequency radio experiments.
