The Large, Oxygen-Rich Halos of Star-Forming Galaxies Are A Major Reservoir of Galactic Metals

TL;DR

This study reveals that star-forming galaxies are surrounded by large, oxygen-rich halos of ionized gas that contain significant amounts of metals and gas, playing a crucial role in galaxy evolution.

Contribution

It provides the first comprehensive observational evidence of massive, metal-enriched halos around star-forming galaxies and their relation to star formation activity.

Findings

Ubiquitous, large ionized oxygen halos around star-forming galaxies.

Less ionized oxygen detected around non-star-forming galaxies.

Halos contain substantial mass of metals and gas, exceeding galaxy reservoirs.

Abstract

The circumgalactic medium (CGM) is fed by galaxy outflows and accretion of intergalactic gas, but its mass, heavy element enrichment, and relation to galaxy properties are poorly constrained by observations. In a survey of the outskirts of 42 galaxies with the Cosmic Origins Spectrograph onboard the Hubble Space Telescope, we detected ubiquitous, large (150 kiloparsec) halos of ionized oxygen surrounding star-forming galaxies, but we find much less ionized oxygen around galaxies with little or no star formation. This ionized CGM contains a substantial mass of heavy elements and gas, perhaps far exceeding the reservoirs of gas in the galaxies themselves. It is a basic component of nearly all star-forming galaxies that is removed or transformed during the quenching of star formation and the transition to passive evolution.