EXTENDED Ly alpha EMISSION FROM INTERACTING GALAXIES AT HIGH REDSHIFTS

Recent observations have discovered a population of extended Ly alpha sources, dubbed Ly alpha blobs (LABs), at high redshift z similar to 2-6.6. These LABs typically have a luminosity of L similar to 10(42)-10(44) erg s(-1), and a size of tens of kiloparsecs, with some giant ones reaching up to D similar to 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 Ly alpha 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 x 10(12) M-circle dot in the redshift range z similar to 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 Ly alpha line emission. We find that intense star formation and enhanced cooling induced by gravitational interaction produce strong Ly alpha emission from these merging galaxies. The Ly alpha 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 similar to 10(3) M-circle dot yr(-1), our model produces LABs with luminosity of L similar to 10(42)-10(44) erg s(-1), and size of D similar to 10-20 kpc at z > 6 and D similar to 20-50 kpc at z similar to 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.