The Simulated Oxygen Shortage (SOS): Mapping the Missing OVI in Simulated Dwarf Galaxies to Subgrid Physics

TL;DR

This study compares different galaxy simulations to understand why they underpredict observed ext{OVI} reservoirs in dwarf galaxy circumgalactic media, highlighting potential issues in oxygen production and metal transport modeling.

Contribution

It identifies that current simulations underproduce oxygen in low-mass galaxies and suggests feedback and metal transport processes need refinement.

Findings

ext{OVI} in simulations mainly arises from cool, diffuse, metal-enriched gas at large radii.

Neither UV background variations nor CGM thermal structure changes resolve the ext{OVI} discrepancy.

Simulations show an underproduction of oxygen compared to star formation history estimates.

Abstract

Observations reveal extended \OVI\, reservoirs in the circumgalactic medium (CGM) of dwarf galaxies, yet current simulations systematically underpredict \OVI\, column densities. Utilizing two suites run with different simulation codes, the \MM\, simulations (Marvelous Massive Dwarfs and Marvel-ous Dwarfs) and the publicly available FIRE-2 simulations, we explore the role of subgrid models and the resulting CGM phase in shaping \OVI\, production. By comparing observationally derived \OVI\, masses to the mass of oxygen produced over the galaxies' star formation history, we find evidence for an underproduction of oxygen for low-mass simulated galaxies. Despite clear differences in feedback implementation, CGM structure, and metal mixing, we find that \OVI\, in both suites generally self-selects cool/warm ($\rm log\, T\,/K \sim 4.5$), diffuse ($\rm log\,n_{gas}\,/cm^{-3} \sim -5.0 $), and moderately metal-enriched ($\rm log\, Z/Z_{\odot} \sim -1 $) material at large radii from the galaxy. We show that neither the choice of ultraviolet background nor plausible variations in CGM thermal structure can close the gap with observations. Taken together, our results point to a possible underproduction of oxygen in low-mass galaxies. Feedback prescriptions contribute via insufficient metal transport to large radii. Hence, the \OVI\, deficit may motivate an investigation of current modeling choices for supernova yields, star formation, and feedback in low-metallicity environments.