The Structure of the Local Interstellar Medium IV: Dynamics, Morphology, Physical Properties, and Implications of Cloud-Cloud Interactions

TL;DR

This paper develops an empirical dynamical model of the local interstellar medium, revealing cloud interactions, morphologies, and physical properties, with implications for understanding the Sun's local environment and cloud dynamics.

Contribution

It provides the first comprehensive dynamical model of the local interstellar medium based on extensive radial-velocity data, characterizing cloud interactions and physical properties.

Findings

15 warm clouds within 15 pc with distinct velocities

Volume filling factor of warm material between 5.5% and 19%

Supersonic relative velocities suggest cloud-cloud interactions

Abstract

We present an empirical dynamical model of the local interstellar medium based on 270 radial-velocity measurements for 157 sight lines toward nearby stars. Physical-parameter measurements (i.e., temperature, turbulent velocity, depletions) are available for 90 components, or one-third of the sample, enabling initial characterizations of the physical properties of LISM clouds. The model includes 15 warm clouds located within 15 pc of the Sun, each with a different velocity vector. We derive projected morphologies of all clouds and estimate the volume filling factor of warm partially ionized material in the LISM to be between ~5.5% and 19%. Relative velocities of potentially interacting clouds are often supersonic, consistent with heating, turbulent, and metal-depletion properties. Cloud-cloud collisions may be responsible for the filamentary morphologies found in ~1/3 of LISM clouds, the distribution of clouds along the boundaries of the two nearest clouds (LIC and G), the detailed shape and heating of the Mic Cloud, the location of nearby radio scintillation screens, and the location of a LISM cold cloud. Contrary to previous claims, the Sun appears to be located in the transition zone between the LIC and G Clouds.