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

TL;DR

This work introduces the Arkenstone-Hot wind implementation in cosmological Arepo simulations to test high-specific-energy winds as a preventative regulator of galaxy growth. By performing a parameter sweep over mass loading $\eta_{\rm M}$ and energy loading $\eta_{\rm E}$, including halo-mass–scaled $\eta_E$, the authors show that wind energy content—not simply ejecta mass—drives the stellar-to-halo mass balance and suppresses in-situ star formation via CGM heating and reduced gas inflow. Compared with the TNG wind model, Arkenstone winds are much lighter but hotter and faster, resulting in substantially different CGM properties: depleted inner CGM, hotter extended halos, and a shift toward preventative feedback. The results suggest that galactic regulation can be achieved with lower SN energy budgets than in previous cosmological simulations and point to future work on metal loading and the full multiphase wind treatment to refine predictions for the CGM/IGM and galaxy scaling relations.

Abstract

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.

Figures (19)

• Figure 1: Mass (top panel) and energy (bottom panel) loadings at $z=0$ for all Arkenstone simulations in this paper, in comparison to scalings from TNG Pillepich2018. Both mass and energy loadings in Arkenstone runs are generally much lower than in TNG. Throughout most plots in this paper, shades of orange show simulations with constant $\eta_\mathrm{E}$ values and fixed $\eta_\mathrm{M}=0.3$; pink/purple lines show simulations with constant $\eta_\mathrm{M}$ values and fixed $\eta_\mathrm{E}=0.3$; shades of blue show simulations with variable energy loading with a fixed $\eta_\mathrm{M}=0.3$. We note that the input loading values actually applied in the simulations for the latter and TNG have an associated scatter, due to the use of the locally measured DM velocity dispersion (and metallicity in the case of TNG) in their calculation. Arkenstone runs with variable energy loadings are capped at an $\eta_\mathrm{E} = 1$.
• Figure 2: Gas surface density maps of the entire simulation box at $z=0$ for the Arkenstone variable energy loading run with $\eta_{\rm E} \propto M_{\rm h}^{-1/3}$ (top panels) and TNG (bottom panels). Zoomed regions highlight two haloes that show particularly different density structures in the two simulations. Gas densities near to galaxies are decreased with Arkenstone, with more gas pushed to large distances.
• Figure 3: Ratio of the surface density maps shown in Fig. \ref{['Fig:DensMap']}, highlighting the differences between the runs. Arkenstone has considerably more gas (shown in orange) in the outskirts of haloes and into the IGM, due to winds extending to large distances from central galaxies. Interestingly, within that the CGM sometimes appears somewhat depleted in Arkenstone compared to TNG (shown in blue).
• Figure 4: Stellar mass functions at $z=0$ for simulations with: 1) constant energy loadings and fixed mass loading of $\eta_{\rm M} = 0.3$ (top panel), 2) constant mass loadings and fixed energy loading of $\eta_{\rm E} = 0.3$ (middle panel), and 3) simulations with variable energy loading with different slopes $\alpha$ and a fixed mass loading of $\eta_{\rm M} = 0.3$ (bottom panel - we remind the reader that we have dropped the redshift dependence on $\eta_{\rm E}$ in this panel for convenience). Each panel also shows the result from TNG (black solid line) and observational data from Bernardi2017 (black dotted line) and Driver2022 (black dashed line). Lines shown are the median of the data, smoothed over the nearest two bins. For the hot, light winds modelled by Arkenstone, energy loading affects the normalisation and slope of the SMF much more than mass loading.
• Figure 5: Ratios of stellar mass to halo mass at $z=0$ as a function of halo mass, normalised by the universal baryon fraction Planck2015Parameters. Median lines have the same styles as Fig. \ref{['fig:z0_SMF']}, with comparison data from Behroozi2019. For the largest haloes in our box we plot individual scatter points, and change our median lines to be dashed. This is to emphasise that results at high masses should be treated with caution, due to the lack of massive haloes and the dominance of the TNG BH model here. Fixed energy loadings tend to overproduce stars at the low mass end, which can be alleviated by introducing a variable energy loading.