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

Abstract

We present an empirical dynamical model of the LISM based on 270 radial velocity measurements for 157 sight lines toward nearby stars. Physical parameter measurements (i.e., temperature, turbulent velocity, depletions) are availablefor90components,orone-thirdof thesample,enablinginitialcharacterizationsof thephysicalpropertiesof 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 intheLISMtobebetween � 5.5%and 19%.Relative velocitiesof potentially interactingclouds areoftensupersonic, consistent with heating, turbulent, and metal depletion properties. Cloud-cloud collisions may be responsible for the filamentary morphologies found in � 1 of LISM clouds, the distribution of clouds along the boundaries of the two nearestclouds(LICandG),thedetailedshapeandheatingof theMicCloud,thelocationof nearbyradioscintillation screens, and the location of an LISM cold cloud. Contrary to previous claims, the Sun appears to be located in the transition zone between the LIC and G Cloud. Subject headingg ISM: atoms — ISM: clouds — ISM: structure — line: profiles — ultraviolet: ISM — ultraviolet: stars