Faint extended Lyalpha emission due to star formation at the centre of
  high-column density QSO absorption systems
  We use detailed Lyalpha radiative transfer calculations to further test the
claim of Rauch et al. (2008) that they have detected spatially extended faint
Lyalpha emission from the elusive host population of Damped Lyalpha Absorption
systems (DLAs) in their recent ultra-deep spectroscopic survey. We investigate
the spatial and spectral distribution of Lyalpha emission due to star-formation
at the centre of DLAs, and its dependence on the spatial and velocity structure
of the gas. Our model simultaneously reproduces the observed properties of DLAs
and the faint Lyalpha emitters, including the velocity width and column density
distribution of DLAs and the large spatial extent of the emission of the faint
emitters. Our modelling confirms previous suggestions that DLAs are
predominately hosted by Dark Matter (DM) halos in the mass range
10^{9.5}-10^{12} M_sun, and are thus of significantly lower mass than those
inferred for L_* Lyman Break Galaxies (LBGs). Our modelling suggests that DM
halos hosting DLAs retain up to 20% of the cosmic baryon fraction in the form
of neutral hydrogen, and that star formation at the centre of the halos is
responsible for the faint Lyalpha emission. The scattering of a significant
fraction of the Lyalpha emission to the observed radii, which can be as large
as 50 kpc or more, requires the amplitude of the bulk motions of the gas at the
centre of the halos to be moderate. The observed space density and size
distribution of the emitters together with the incidence rate of DLAs suggests
that the Lyalpha emission due to star formation has a duty cycle of ~ 25%.
