Recent observations have discovered a population of extended Lyα sources, dubbed Lyα blobs (LABs), at high redshift z ∼ 2-6.6. These LABs typically have a luminosity of L ∼ 1042-1044 erg s-1, 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 Lyα 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 × 1012 M ⊙ in the redshift range z ∼ 3-7, and we use the newly improved ART2 code to perform the radiative transfer calculations, which couple multi-wavelength continuum, ionization of hydrogen, and Lyα line emission. We find that intense star formation and enhanced cooling induced by gravitational interaction produce strong Lyα emission from these merging galaxies. The Lyα 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 ∼103 M ⊙ yr-1, our model produces LABs with luminosity of L ∼ 1042-1044 erg s-1, 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.
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science