Zooming in on the circumgalactic medium with GIBLE: Cloud-scale simulations with cosmological initial conditions

TL;DR

This study uses high-resolution, cosmologically motivated simulations to investigate the evolution and survival of cool clouds in the circumgalactic medium, highlighting the importance of initial conditions and physical processes like radiative cooling.

Contribution

It introduces a targeted refinement scheme for simulating small-scale clouds within cosmological initial conditions, providing new insights into cloud dynamics and survival mechanisms.

Findings

Radiative cooling is crucial for cloud survival.

Magnetic fields have a smaller impact compared to cooling.

Cloud motion is influenced by complex background velocity fields.

Abstract

We conduct simulations of $\sim$kpc-scale cool clouds in the circumgalactic medium (CGM), using initial conditions sampled from a highly resolved cosmological magneto-hydrodynamical zoom-in of a Milky Way-like galaxy. We select ten distinct cold clouds with masses of $m_{\rm{cloud}}$ $\sim$ $10^{4.5-5}$ M$_\odot$, originally resolved at a mass resolution of $m_{\rm{gas}}$ $\sim$ $200$ M$_\odot$. To further resolve small-scale features and physics, we implement a targeted refinement scheme within spherical regions co-moving with each cloud, thereby boosting the local mass resolution by a factor of 1000, reaching $m_{\rm{gas}}$ $\sim$ $0.2$ M$_\odot$ (spatial resolution, $r_{\rm{gas,cloud}}$ $\sim$ $O(\rm{pc})$). The selected clouds have diverse properties, across a broad parameter space, resulting in heterogeneous evolution. For the clouds we study, radiative cooling is the dominant physical process enabling cloud survival, while magnetic fields play a comparatively smaller role. The motion of these clouds is governed not only by drag forces that decelerate them, but also by acceleration from momentum exchange with the complex background velocity field, which can cause them to move faster than ballistic projectiles set by their initial velocities. Our results suggest that the non-trivial details of realistic cosmological initial conditions -- specifically the complex density, temperature, and velocity fields -- may play an important role in subsequent cloud evolution, and that sampling the output of an existing large-scale simulation provides a self-consistent approach to capture these effects without ad hoc assumptions.