Probing dark energy with future redshift surveys: A comparison of
  emission line and broad band selection in the near infrared
  Future galaxy surveys will map the galaxy distribution in the redshift
interval $0.5<z<2$ using near-infrared cameras and spectrographs. The primary
science goal of such surveys is to constrain the nature of the dark energy by
measuring the large-scale structure of the Universe. This requires a tracer of
the underlying dark matter which maximizes the useful volume of the survey. We
investigate two potential survey selection methods: an emission line sample
based on the \ha line and a sample selected in the H-band. We present
predictions for the abundance and clustering of such galaxies, using two
published versions of the \galform galaxy formation model. Our models predict
that \ha selected galaxies tend to avoid massive dark matter haloes and instead
trace the surrounding filamentary structure; H-band selected galaxies, on the
other hand, are found in the highest mass haloes. This has implications for the
measurement of the rate at which fluctuations grow due to gravitational
instability. We use mock catalogues to compare the effective volumes sampled by
a range of survey configurations. To give just two examples: a redshift survey
down to $H_{\rm AB}=22$ samples an effective volume that is $\sim 5-10$ times
larger than that probed by an \ha survey with $\logfha > -15.4$; a flux limit
of at least $\logfha = -16$ is required for an \ha sample to become competitive
in effective volume.
