Probing high-redshift galaxies with Ly$\alpha$ intensity mapping
  We present a study of the cosmological Ly$\alpha$ emission signal at $z > 4$.
Our goal is to predict the power spectrum of the spatial fluctuations that
could be observed by an intensity mapping survey. The model uses the latest
data from the HST legacy fields and the abundance matching technique to
associate UV emission and dust properties with the halos, computing the
emission from the interstellar medium (ISM) of galaxies and the intergalactic
medium (IGM), including the effects of reionization, self-consistently. The
Ly$\alpha$ intensity from the diffuse IGM emission is 1.3 (2.0) times more
intense than the ISM emission at $z = 4(7)$; both components are fair tracers
of the star-forming galaxy distribution. However the power spectrum is
dominated by ISM emission on small scales ($k > 0.01 h{\rm Mpc}^{-1}$) with
shot noise being significant only above $k = 1 h{\rm Mpc}^{-1}$. At very lange
scales ($k < 0.01h{\rm Mpc}^{-1}$) diffuse IGM emission becomes important. The
comoving Ly$\alpha$ luminosity density from IGM and galaxies, $\dot \rho_{{\rm
Ly}\alpha}^{\rm IGM} = 8.73(6.51) \times 10^{40} {\rm erg}{\rm s}^{-1}{\rm
Mpc}^{-3}$ and $\dot \rho_{{\rm Ly}\alpha}^{\rm ISM} = 6.62(3.21) \times
10^{40} {\rm erg}{\rm s}^{-1}{\rm Mpc}^{-3}$ at $z = 4(7)$, is consistent with
recent SDSS determinations. We predict a power $k^3 P^{{\rm Ly}\alpha}(k,
z)/2\pi^2 = 9.76\times 10^{-4}(2.09\times 10^{-5}){\rm nW}^2{\rm m}^{-4}{\rm
sr}^{-2}$ at $z = 4(7)$ for $k = 0.1 h {\rm Mpc}^{-1}$.
