ARCHITECTS II: Impact of subgrid physics on the observable properties of the circumgalactic medium

TL;DR

This study compares three different subgrid physics models in cosmological simulations to understand their impact on the circumgalactic medium's observable properties, revealing how feedback mechanisms influence gas phases and absorption features.

Contribution

It introduces a comparative analysis of subgrid feedback models in galaxy simulations, highlighting their effects on CGM observables and identifying diagnostics for model differentiation.

Findings

Different feedback models produce distinct CGM properties despite similar stellar masses.

Column densities and covering fractions effectively diagnose subgrid model differences.

All models struggle to fully reproduce observed absorption features, indicating missing physics.

Abstract

Galaxy evolution is driven by star formation and stellar feedback on scales unresolved by current high-resolution cosmological simulations, requiring robust subgrid models. However, these models remain degenerate, often calibrated primarily to match observed stellar masses. To explore these degeneracies, we conduct three state-of-the-art cosmological zoom-in simulations of the same galaxy, each incorporating different subgrid models: mechanical feedback, a combination of mechanical and thermal feedback, and delayed cooling. We compare their circumgalactic media (CGM) through quasar absorption sightlines of HI, MgII, CIV, and OVI. Our findings demonstrate that despite producing galaxies with the same stellar masses, the models lead to distinct feedback modes and CGM properties. Column densities and covering fractions serve as effective diagnostics of subgrid models, with all four ions providing strong constraints as they trace diverse gas phases, exhibit complementary spatial distributions, and originate from different mechanisms. Although all simulations bracket observed column density distributions, direct comparisons are limited by scarce detections and significant scatter in absorption strengths. Covering fractions of weak absorbers provides the most robust constraints. All models fail to reproduce HI and MgII covering fractions, and delayed cooling overproduces OVI covering fractions, while the other models underproduce them. The simulation including mechanical feedback reproduces the observed CIV covering fractions well, whereas the other models show slight offsets. We argue that this discrepancy is likely driven by unresolved thermal structures for HI and MgII, and insufficient metals for CIV and OVI, arising from missing physics such as AGNs or cosmic rays.