Extended Lyman-alpha emission from interacting galaxies at high redshifts

TL;DR

This study uses hydrodynamic simulations and radiative transfer calculations to explore how galaxy mergers at high redshift can produce extended Lyman-alpha emission, potentially explaining observed Lyman-alpha blobs.

Contribution

It introduces a merger model for LAB formation, combining advanced simulations with radiative transfer to match observed properties of high-redshift LABs.

Findings

Merging galaxies produce strong, extended Lya emission during peak star formation.

Simulated LAB sizes and luminosities align with observations at z > 6 and z ~ 3.

Giant LABs may require more massive mergers or additional processes.

Abstract

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.