Filamentary Infall of Cold Gas and Escape of Lyman Alpha and Hydrogen Ionizing Radiation from an Interacting High-Redshift Galaxy

TL;DR

This study observes a high-redshift galaxy revealing gas inflow and radiation escape processes, providing insights into early galaxy formation and reionization, with evidence of cold gas accretion and ionizing photon escape.

Contribution

It presents detailed observations of a peculiar galaxy showing gas inflow and radiation escape, highlighting the role of galaxy interactions in early universe reionization.

Findings

Detection of extended, asymmetric Lyman alpha emission with absorption features.

Evidence for cold gas inflow in the form of a narrow filament.

High escape fraction (~50%) of ionizing photons from the galaxy.

Abstract

We present observations of a peculiar Lyman alpha-emitting galaxy at redshift 3.344, discovered in a deep, blind spectroscopic survey for faint Lyman alpha emitters with the Magellan II telescope in the Hubble Ultra Deep Field (HUDF). The galaxy exhibits complex Lyman alpha emission, including an extended, asymmetric component that is partially suppressed by damped Lyman alpha absorption, and two spatially elongated, narrow emission features. Archival HST ACS imaging shows evidence for tidal disruption of the stellar component. This V=27 galaxy appears to give us unprecedented insights into two fundamental stages in the formation of structure at high redshift: the inflow of gas into ordinary galaxies, and the escape of ionizing radiation into the intergalactic medium. Neutral hydrogen, falling in partly in form of a narrow filament, appears to emit fluorescent Lyman alpha photons induced by the stellar ionizing flux escaping from the disturbed galaxy. The in-falling material may represent primary cold accretion or an interaction-triggered inflow. The rate of ionizing photons required by the observed Lyman alpha emission is consistent with the rate of photons produced by the observed stellar population, with roughly 50 percent of ionizing photons escaping from the immediate galaxy and encountering the in-falling gas. The observational properties of the galaxy lend support to a picture where galaxy interactions facilitate the escape of both Lyman alpha and ionizing radiation. We argue that galaxies like the present object may be common at high redshift. This galaxy may therefore be a late example of an interacting population of dwarf galaxies contributing significantly to the reionization of the universe.