Star formation and the interstellar medium in z>6 UV-luminous Lyman-break galaxies

TL;DR

This study uses ALMA observations to analyze star formation and interstellar medium properties in UV-luminous galaxies at redshift 6, revealing evolving dust characteristics, high [CII]/FIR ratios, and complex merger structures, challenging previous assumptions about Lyman alpha velocities.

Contribution

First detailed ALMA analysis of atomic carbon and dust in z>6 UV-luminous galaxies, showing dust evolution and complex merger features at high redshift.

Findings

Higher [CII]/FIR ratios than low-redshift counterparts

No decrease in Lyman alpha velocity shifts at high redshift

Evidence of galaxy mergers with distinct UV and FIR emission components

Abstract

We present Atacama Large Millimeter Array (ALMA) detections of atomic carbon line and dust continuum emission in two UV-luminous galaxies at redshift 6. The far-infrared (FIR) luminosities of these galaxies are substantially lower than similar starbursts at later cosmic epochs, indicating an evolution in the dust properties with redshift, in agreement with the evolution seen in ultraviolet (UV) attenuation by dust. The [CII] to FIR ratios are found to be higher than at low redshift showing that [CII] should be readily detectable by ALMA within the reionization epoch. One of the two galaxies shows a complex merger nature with the less massive component dominating the UV emission and the more massive component dominating the FIR line and continuum. Using the interstellar atomic carbon line to derive the systemic redshifts we investigate the velocity of Lyman alpha emission emerging from high-z galaxies. In contrast to previous work, we find no evidence for decreasing Lyman alpha velocity shifts at high-redshift. We observe an increase in velocity shifts from z$\sim$2 to z$\sim$6, consistent with the effects of increased IGM absorption.