Figuring Out Gas &amp; Galaxies in Enzo (FOGGIE). XI. Circumgalactic O <scp>VI</scp> Emission Traces Clumpy Inflowing Recycled 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 → 0. 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 ∼ 10 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 toward 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 kiloparsecs from the galaxy center for ∼ L ⋆ galaxies.