Extended Lyman-alpha emission from interacting galaxies at high
  redshifts
  Recent observations have discovered a population of extended Lya sources,
dubbed Lyman-alpha blobs (LABs), at high redshift z ~ 3 - 6.6. These LABs
typically have a luminosity of L ~ 10^42-10^44 erg/s, and a size of tens of
kiloparsecs, with some giant ones reaching up to D ~ 100 kpc. However, the
origin of these LABs is not well understood. In this paper, we investigate a
merger model for the formation of LABs by studying Lya emission from
interacting galaxies at high redshifts by means of a combination of
hydrodynamics simulations with three dimensional radiative transfer
calculations. Our galaxy simulations focus on a set of binary major mergers of
galaxies with a mass range of 3-7 *10^12 Msun in the redshift range of z ~ 3
-7, and we use the newly improved ART^2 code to perform the radiative transfer
calculations which couple multi-wavelength continuum, ionization of hydrogen,
and Lya line emission. We find that intense star formation and enhanced cooling
induced by gravitational interaction produce strong Lya emission from these
merging galaxies. The Lya emission appears to be extended due to the extended
distribution of sources and gas. During the close encounter of galaxy
progenitors when the star formation rate peaks at ~ 10^3 Msun/yr, our model
produces Lya blobs with luminosity of L ~ 10^42-10^44 erg/s, and size of D ~
10-20 kpc at z>6 and D ~ 20-50 kpc at z ~ 3, in broad agreement with
observations in the same redshift range. Our results suggest that merging
galaxies may produce some typical LABs as observed, but the giant ones may be
produced by mergers more massive than those in our model, or a combination of
mergers and cold accretion from filaments on a large scale.
