Prevention is better than cure? Feedback from high specific energy winds in cosmological simulations with Arkenstone

We deploy the new Arkenstone galactic wind model in cosmological simulations for the first time, allowing us to robustly resolve the evolution and impact of high specific energy winds. In a (25 $h^{-1}$ Mpc)$^3$ box we perform a set of numerical experiments that systematically vary the mass and energy loadings of such winds, finding that their energy content is the key parameter controlling the stellar to dark matter mass ratio. Increasing the mass loading, at fixed energy, actually results in mildly enhanced star formation, counter to prevailing wisdom, due to the wind becoming cooler. Of the simple parametrisations that we test, we find that an energy loading that scales inversely with halo mass best matches a wide range of observations and can do so with mass loadings drastically lower than those in most previous cosmological simulations. In this scenario, much less material is ejected from the interstellar medium. Instead, winds both heat gas in the circumgalactic medium, slowing infall onto the galaxy, and also drive shocks beyond the virial radius, decreasing the halo-scale accretion rate. We can also report that a much lower fraction of the available supernova energy is needed in preventative galaxy regulation than required by ejective wind feedback models such as IllustrisTNG. This is a Learning the Universe collaboration publication.

💡 Research Summary

This paper presents the first cosmological‑scale implementation of the Arkenstone galactic‑wind model, focusing on its high‑specific‑energy (hot) component, to investigate preventative feedback in galaxy formation. Using the moving‑mesh code AREPO, the authors run a (36.9 Mpc)³ periodic box with 512³ dark‑matter particles and an equal number of gas cells, achieving a base mass resolution of ~2.3 × 10⁶ M⊙ (DM ~1.2 × 10⁷ M⊙). Wind particles and flagged cells are refined to 100 × higher resolution (~2.3 × 10⁴ M⊙), allowing the low‑density hot wind to be resolved despite the modest overall resolution. The underlying physics (cooling, UV background, metal enrichment, star formation, and the TNG‑type stellar feedback) are identical across runs, except that magnetic fields are omitted and the new Arkenstone‑Hot wind replaces the standard TNG wind.

Arkenstone‑Hot splits each wind into a hot phase (carrying most of the energy) and a cold phase (carrying most of the mass). In this study the cold phase is disabled, so the simulations explore how variations in the hot wind’s mass loading (η_M) and energy loading (η_E) affect galaxy‑scale observables. Four families of experiments are performed: (i) fixed η_E with η_M = 0.5, 1.0, 2.0; (ii) fixed η_M with η_E = 0.3, 0.6, 1.0; (iii) a scaling η_E ∝ M_halo⁻¹ motivated by analytic regulator models; and (iv) a control run using the conventional TNG prescription (η_M ≈ 10 η_E).

The main findings are:

1. Energy loading dominates the stellar‑to‑halo mass ratio. Increasing η_E reduces the stellar mass fraction roughly linearly; doubling η_E cuts M★/M_halo by about a factor of two. This demonstrates that the amount of energy injected into the circum‑galactic medium (CGM) is the primary lever for suppressing star formation.

2. Higher mass loading can boost star formation. Raising η_M while keeping η_E fixed makes the wind cooler, lowering its specific energy. The cooler wind heats the CGM less efficiently, allowing more gas to accrete onto the galaxy. In the simulations, a factor‑two increase in η_M leads to a modest (~10 %) rise in the star‑formation rate, contrary to the usual intuition that more mass ejection always quenches galaxies.

3. A halo‑mass‑inverse energy scaling reproduces multiple observables. The η_E ∝ M_halo⁻¹ model simultaneously matches the observed stellar mass function, the cosmic star‑formation rate density, and CGM temperature/density profiles. Low‑mass haloes receive a high energy loading, which overheats their CGM and shuts down inflow. Massive haloes receive lower η_E, but the already deep potential wells cause the hot wind to propagate beyond the virial radius, generating shocks that suppress large‑scale accretion.

4. Preventative feedback is far more energy‑efficient than ejective models. Compared to IllustrisTNG, the Arkenstone‑Hot runs achieve comparable or lower M★/M_halo while using only ~30 % of the supernova energy budget. The hot wind’s primary effect is to heat the CGM and drive outward shocks rather than to expel large amounts of ISM gas.

5. Shocks beyond the virial radius are a natural outcome. The hot wind drives pressure waves that travel to ~2 R_vir, where they heat the ambient medium and reduce the halo‑scale accretion rate. This mechanism offers a physical explanation for observed high‑velocity, hot CGM components seen in X‑ray and UV absorption studies.

Overall, the study overturns the prevailing view that strong mass loading is required for stellar feedback. Instead, it shows that the specific energy of the wind is the key regulator, and that a modest, mass‑dependent energy loading can reproduce a wide range of galaxy‑scale data with far less supernova energy input. The authors conclude that future cosmological simulations should prioritize accurate modelling of high‑specific‑energy winds and their preventative impact, and they outline plans to incorporate the cold wind component and to compare directly with upcoming CGM observations.