The Impact of Star Formation Feedback on the Circumgalactic Medium

TL;DR

This study uses 3D hydrodynamic simulations to explore how star formation feedback influences the structure and dynamics of the circumgalactic medium across different galaxy halo masses, revealing a critical mass where properties change.

Contribution

It provides a detailed analysis of the physical processes shaping the CGM, highlighting the role of feedback and identifying a critical halo mass that alters the dominant support mechanisms.

Findings

CGM properties change markedly near a halo mass of ~10^{11.5} M_sun.

Above the critical mass, thermal pressure supports the halo; below, bulk flows dominate.

Simulations reproduce some observed properties of the multiphase CGM, but underpredict neutral hydrogen.

Abstract

We use idealized 3D hydrodynamic simulations to study the dynamics and thermal structure of the circumgalactic medium (CGM). Our simulations quantify the role of cooling, stellar feedback driven galactic winds and cosmological gas accretion in setting the properties of the CGM in dark matter haloes ranging from $10^{11}$ to $10^{12}$ M$_\odot$. Our simulations support a conceptual picture in which the properties of the CGM, and the key physics governing it, change markedly near a critical halo mass of M$_{\rm crit} \approx 10^{11.5}$ M$_\odot$. As in calculations without stellar feedback, above M$_{\rm crit}$ halo gas is supported by thermal pressure created in the virial shock. The thermal properties at small radii are regulated by feedback triggered when $t_{\rm cool}/t_{\rm ff}\lesssim10$ in the hot gas. Below M$_{\rm crit}$, however, there is no thermally supported halo and self-regulation at $t_{\rm cool}/t_{\rm ff}\sim10$ does not apply. Instead, the gas is out of hydrostatic equilibrium and largely supported against gravity by bulk flows (turbulence and coherent inflow/outflow) arising from the interaction between cosmological gas inflow and outflowing galactic winds. In these lower mass haloes, the phase structure depends sensitively on the outflows' energy per unit mass and mass-loading, which may allow measurements of the CGM thermal state to constrain the nature of galactic winds. Our simulations account for some of the properties of the multiphase halo gas inferred from quasar absorption line observations, including the presence of significant mass at a wide range of temperatures, and the characteristic OVI and CIV column densities and kinematics. However, we underpredict the neutral hydrogen content of the $z\sim0$ CGM.