The Impact of Type Ia Supernovae in Quiescent Galaxies: II. Energetics and Turbulence

TL;DR

This study uses high-resolution simulations to reveal that Type Ia supernovae significantly enhance heating and turbulence in quiescent galaxy media, producing large density contrasts and complex velocity fields that impact X-ray observations.

Contribution

The paper demonstrates the distinct effects of resolved SNe Ia remnants on galactic media, highlighting increased heating, turbulence, and density fluctuations compared to unresolved models.

Findings

Net heating exceeds expectations by 30±10% per cooling time.

Gas velocities reach 20-50 km/s with dominant compressional modes.

Density fluctuations are broader than previously observed, with high $b$ values.

Abstract

Type Ia supernovae (SNe Ia) provide unique and important feedback in quiescent galaxies, but their impact has been underappreciated. In this paper, we analyze a series of high-resolution simulations to examine the energetics and turbulence of the medium under SNe Ia. We find that when SN remnants are resolved, their effects differ distinctly from a volumetric heating term, as is commonly assumed in unresolved simulations. First, the net heating is significantly higher than expected, by 30$\pm$10\% per cooling time. This is because a large fraction of the medium is pushed into lower densities which cool inefficiently. Second, the medium is turbulent; the root-mean-squared (RMS) velocity of the gas to 20-50 km s$^{-1}$ on a driving scale of tens of parsec. The velocity field of the medium is dominated by compressional modes, which are larger than the solenoidal components by a factor of 3-7. Third, the hot gas has a very broad density distribution. The ratio between the density fluctuations and the RMS Mach number, parameterized as $b$, is 2-20. This is in contrast to previous simulations of turbulent media, which have found $b\lesssim$ 1. The reason for the difference is mainly caused by the \textit{localized} heating of SNe Ia, which creates a large density contrast. Last, the typical length scale of a density fluctuation grows with time, forming increasingly larger bubbles and filamentary ridges. These underlying density fluctuations need to be included when X-ray observations are interpreted.