How High-Specific-Energy Winds Regulate the Circumgalactic Medium of Dwarf Galaxies

TL;DR

This study uses cosmological simulations to show how high-specific-energy supernova-driven winds regulate the circumgalactic medium of dwarf galaxies, balancing ejective and preventive feedback over cosmic time.

Contribution

It demonstrates the impact of episodic, high-energy supernova feedback on CGM heating, outflow composition, and baryon regulation in dwarf galaxy halos.

Findings

Hot outflows dominate energy transfer and escape the halo.

Warm outflows recycle back into the ISM fueling star formation.

A transition at ~5 Gyr shifts feedback from ejective to preventive mode.

Abstract

We investigate the role of ejective and preventive feedback in $\mathrm{\sim10^{10}-10^{11}\,M_\odot}$ dwarf halos using cosmological zoom-in simulations. These simulations use adaptive mesh refinement to capture high-specific-energy outflows, together with an implementation of discrete supernovae (SNe). We show that episodic, SNe-driven shock heating sustains the circumgalactic medium (CGM) at $\mathrm{\sim T_{vir}}$. This process also increases the ratio $\mathrm{t_{cool}/t_{ff} > 10}$ in the outer CGM and intergalactic medium (IGM), placing the gas in a radiatively stable regime. Hot outflows ($\mathrm{\gtrsim10^5\, K}$) dominate the energy budget, and their high specific energy allows them to traverse the CGM, escape the halo, and heat the IGM. In contrast, warm outflows ($\mathrm{\lesssim10^5\, K}$) dominate the mass budget and are largely recycled back into the interstellar medium (ISM), where they fuel future star formation. We identify a gradual transition at $\mathrm{\sim 5\, Gyr}$ that marks a shift in the balance between ejective and preventive feedback. At early times ($\mathrm{< 5\, Gyr}$), although the CGM cooling rate dominates for a larger fraction of time, the infrequent yet powerful SNe energy injection into the CGM is able to quickly dominate the cumulative energy balance. These outflows and their high specific energy are able to 'sweep' up mass in the CGM and IGM. At late times ($\mathrm{> 5\, Gyr}$), the CGM baryon fraction is only $\mathrm{\sim0.1}$, leading to a transition toward a preventive feedback mode in which SNe maintain $\mathrm{t_{cool}/t_{ff} > 10}$ and prevent $\mathrm{\sim75\%}$ of the expected baryon accretion rate.