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Recent observations have discovered a population of extended Lya sources,dubbed Lyman-alpha blobs (LABs), at high redshift z ~ 3 - 6.6. These LABstypically have a luminosity of L ~ 10^42-10^44 erg/s, and a size of tens ofkiloparsecs, with some giant ones reaching up to D ~ 100 kpc. However, theorigin of these LABs is not well understood. In this paper, we investigate amerger model for the formation of LABs by studying Lya emission frominteracting galaxies at high redshifts by means of a combination ofhydrodynamics simulations with three dimensional radiative transfercalculations. Our galaxy simulations focus on a set of binary major mergers ofgalaxies 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 transfercalculations which couple multi-wavelength continuum, ionization of hydrogen,and Lya line emission. We find that intense star formation and enhanced coolinginduced by gravitational interaction produce strong Lya emission from thesemerging galaxies. The Lya emission appears to be extended due to the extendeddistribution of sources and gas. During the close encounter of galaxyprogenitors when the star formation rate peaks at ~ 10^3 Msun/yr, our modelproduces 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 withobservations in the same redshift range. Our results suggest that merginggalaxies may produce some typical LABs as observed, but the giant ones may beproduced by mergers more massive than those in our model, or a combination ofmergers and cold accretion from filaments on a large scale.

Extended Lyman-alpha emission from interacting galaxies at high redshifts