Extended Lyman-Alpha Emission around Star-forming Galaxies

TL;DR

This paper predicts the extended Lyman-alpha emission around high-redshift star-forming galaxies using radiative transfer models, highlighting its detectability and dependence on galaxy properties, which can inform understanding of the circumgalactic medium.

Contribution

It provides the first detailed radiative transfer predictions of extended Lyman-alpha emission profiles around galaxies in a cosmological simulation.

Findings

Extended emission has a central cusp, then flattens, then steepens beyond ~1 Mpc.

Inner and outer scales of emission increase with galaxy mass and luminosity.

Predicted emission is detectable with current deep narrowband imaging.

Abstract

Lyman-alpha (Lya) photons that escape the interstellar medium of star-forming galaxies may be resonantly scattered by neutral hydrogen atoms in the circumgalactic and intergalactic media, thereby increasing the angular extent of the galaxy's Lya emission. We present predictions of this extended, low surface brightness Lya emission based on radiative transfer modeling in a cosmological reionization simulation. The extended emission can be detected from stacked narrowband images of Lya emitters (LAEs) or of Lyman break galaxies (LBGs). Its average surface brightness profile has a central cusp, then flattens to an approximate plateau beginning at an inner characteristic scale below ~0.2 Mpc (comoving), then steepens again beyond an outer characteristic scale of ~1 Mpc. The inner scale marks the transition from scattered light of the central source to emission from clustered sources, while the outer scale marks the spatial extent of scattered emission from these clustered sources. Both scales tend to increase with halo mass, UV luminosity, and observed Lya luminosity. The extended emission predicted by our simulation is already within reach of deep narrowband photometry using large ground-based telescopes. Such observations would test radiative transfer models of emission from LAEs and LBGs, and they would open a new window on the circumgalactic environment of high-redshift star-forming galaxies.