The Interstellar Medium In Galaxies Seen A Billion Years After The Big Bang

TL;DR

This study measures [CII] gas and dust emission in nine early galaxies around 1 billion years after the Big Bang, revealing significant evolution in their interstellar medium properties compared to later epochs.

Contribution

First direct measurements of [CII] and dust emission in typical galaxies at z~5-6, demonstrating strong evolution in interstellar medium characteristics in the early universe.

Findings

Galaxies have >12x less thermal emission than similar systems at z~2.

Enhanced [CII] emission relative to far-infrared continuum observed.

Gas distributed over 1-8 kpc with diverse dynamics.

Abstract

Evolution in the measured rest frame ultraviolet spectral slope and ultraviolet to optical flux ratios indicate a rapid evolution in the dust obscuration of galaxies during the first 3 billion years of cosmic time (z>4). This evolution implies a change in the average interstellar medium properties, but the measurements are systematically uncertain due to untested assumptions, and the inability to measure heavily obscured regions of the galaxies. Previous attempts to directly measure the interstellar medium in normal galaxies at these redshifts have failed for a number of reasons with one notable exception. Here we report measurements of the [CII] gas and dust emission in 9 typical (~1-4L*) star-forming galaxies ~1 billon years after the big bang (z~5-6). We find these galaxies have >12x less thermal emission compared with similar systems ~2 billion years later, and enhanced [CII] emission relative to the far-infrared continuum, confirming a strong evolution in the interstellar medium properties in the early universe. The gas is distributed over scales of 1-8 kpc, and shows diverse dynamics within the sample. These results are consistent with early galaxies having significantly less dust than typical galaxies seen at z<3 and being comparable to local low-metallicity systems.