Figuring Out Gas & Galaxies In Enzo (FOGGIE) XI: Circumgalactic O VI Emission Traces Clumpy Inflowing Recycled Gas

TL;DR

This study uses simulations to predict O VI emission in the circumgalactic medium, revealing it traces inflowing, metal-enriched gas around galaxies, with implications for upcoming observational missions.

Contribution

It provides the first detailed predictions of O VI emission properties in the CGM across redshifts, linking emission to inflowing gas and feedback processes.

Findings

O VI emission is brightest near dense, clumpy inflowing gas structures.

Higher galaxy mass and star formation rates lead to brighter, more widespread O VI emission.

Feedback-driven enrichment is essential for O VI emission in inflowing gas.

Abstract

The circumgalactic medium (CGM) is host to gas flows into and out of galaxies and regulates galaxy growth, but the multiphase, diffuse gas in this region is challenging to observe. We investigate the properties of gas giving rise to O VI emission from the CGM that upcoming missions, such as the Aspera SmallSat, will be able to map in local galaxies. We use the FOGGIE simulations to predict the O VI emission from edge-on galaxies across the redshift range $z=1\rightarrow0$. O VI emission is brightest surrounding small, clumpy structures near the galaxy where the gas density is high. Most of the O VI surface brightness originates from collisionally ionized, $T\sim10^{5.5}$ K, inflowing gas and is not preferentially aligned with the major or minor axis of the galaxy disk. Simulated galaxies with higher halo masses, higher median CGM gas density, and higher star formation rates produce brighter and more widespread O VI emission in their CGM. We show that while O VI emission primarily originates in inflowing gas, turning off outflows in a simulation without star formation feedback eliminates most of the O VI emission. Enrichment from feedback is necessary to mix with the inflowing gas and allow it to glow in O VI. Collectively, our findings point towards a picture where O VI emission traces warm, ionized envelopes of cooler clouds that are accreting onto the galaxy in a metal-enriched galactic fountain. Finally, we show that the detection limit of Aspera is sufficient to detect O VI emission tens of kpc from the galaxy center for $\sim L^\star$ galaxies.