X-ray signatures of galactic outflows into the circumgalactic medium

TL;DR

This study uses hydrodynamical simulations to analyze how strong galactic outflows influence the density, temperature, and X-ray signatures of circumgalactic gas, revealing thresholds where outflows significantly alter observable X-ray emissions.

Contribution

The paper introduces controlled hydrodynamical simulations exploring the impact of galactic outflows on the circumgalactic medium's X-ray signatures, considering various initial states and energy injection rates.

Findings

Outflows with energy >10^{41}-10^{42} erg/s produce dominant X-ray signatures from shock-heated gas.

X-ray surface brightness is affected by outflows primarily at higher energy injection rates.

Analytic models for shock propagation and X-ray emission are provided.

Abstract

We present a set of controlled hydrodynamical simulations to study the effects of strong galactic outflows on the density and temperature structures, and associated X-ray signatures, of extra-planar and circumgalactic gas. We consider three initial state models, isothermal, isentropic, and rotating cooling-flow, for the hot circumgalactic medium (CGM) into which the outflows are driven. The energy sources are either stellar winds and supernovae, or active galactic nuclei. We consider energy injection rates in the range $10^{40} < \dot{E}_{\rm inj} <10^{44.5}$ erg s$^{-1}$, and compute the time-dependent soft X-ray (0.5-2 keV) surface brightness. For $\dot{E}_{\rm inj} \gtrsim 10^{41} - 10^{42}$ erg s$^{-1}$, with the exact threshold depending on the initial CGM state, the X-ray response is dominated by dense hot gas in the forward shock that eventually fades into the CGM as a sound wave. The shock surrounds an inner hot bubble leading to a radial flattening of the X-ray surface brightness. For lower energy injection rates, the X-ray surface brightness of the initial CGM state is almost unaffected. We present analytic approximations for the outflow shock propagation and the associated X-ray emissions.