Constraints on galactic wind models

TL;DR

This paper compares two models of supernova-driven galactic winds, deriving observational constraints and suggesting thermal evaporation as a key mass-loading process, with implications for galaxy evolution and observable signatures.

Contribution

It provides a detailed analysis of galactic wind models, linking theoretical predictions with observational data, and highlights thermal evaporation as a significant mass-loading mechanism.

Findings

Steady-state wind models match observed X-ray luminosity and star formation rate correlations.

Thermal evaporation from superbubble walls can supply the required mass-loading.

Both models can explain radio luminosities of starburst galaxies.

Abstract

Observational implications are derived for two standard models of supernovae-driven galactic winds: a freely expanding steady-state wind and a wind sourced by a self-similarly expanding superbubble including thermal heat conduction. It is shown that, for the steady-state wind, matching the measured correlation between the soft x-ray luminosity and star formation rate of starburst galaxies is equivalent to producing a scaled wind mass-loading factor relative to the star-formation rate of 0.5 - 3, in agreement with the amount inferred from metal absorption line measurements. The match requires the asymptotic wind velocity v_inf to scale with the star formation rate SFR (in solar masses per year) approximately as v_inf ~ (700 - 1000) km/s SFR^{1/6}. The corresponding mass injection rate is close to the amount naturally provided by thermal evaporation from the wall of a superbubble in a galactic disc, suggesting thermal evaporation may be a major source of mass-loading. The predicted mass-loading factors from thermal evaporation within the galactic disc alone, however, are somewhat smaller, 0.2 - 2, so that a further contribution from cloud ablation or evaporation may be required. Both models may account for the 1.4GHz luminosity of unresolved radio sources within starburst galaxies for plausible parameters describing the distribution of relativistic electrons. Further observational tests to distinguish the models are suggested.