Non-Gravitational Contributions to the Clustering of Ly-alpha Selected
  Galaxies: Implications for Cosmological Surveys
  We show that the dependence of Ly-alpha absorption on environment leads to
significant non-gravitational features in the redshift space power-spectrum of
Ly-alpha selected galaxies. We derive a physically motivated fitting formula
that can be included in clustering analyses, and use this to discuss the
predicted features in the Ly-alpha galaxy power-spectrum based on detailed
models in which Ly-alpha absorption is influenced by gas infall and/or by
strong galactic outflows. We show that power-spectrum measurements could be
used to study the astrophysics of the galaxy-IGM connection, and to measure the
properties of outflows from star-forming galaxies. Applying the modified
redshift space power-spectrum to a Ly-alpha survey with parameters
corresponding to the planned Hobby-Eberly Telescope Dark Energy Experiment
(HETDEX), we find that the dependence of observed Ly-alpha flux on velocity
gradient and ionising background may compromise the ability of Ly-alpha
selected galaxy redshift surveys to constrain cosmology using information from
the full power-spectrum. This is because the effects of fluctuating ionizing
background and velocity gradients effect the shape of the observed
power-spectrum in ways that are similar to the shape of the primordial
power-spectrum and redshift space distortions respectively. We use the
Alcock-Paczynski test to show that without prior knowledge of the details of
Ly-alpha absorption in the IGM, the precision of line-of-sight and transverse
distance measurements for HETDEX will be ~1.3-1.7%, decreased by a factor of
~1.5-2 relative to the best case precision of ~0.8% available in a traditional
galaxy redshift survey. We specify the precision with which modelling of
Ly-alpha radiative transfer must be understood in order for HETDEX to achieve
distance measurements that are better than 1%.
