Warm and Hot Gas in the Local ISM

Abstract

I present a short review of the physical properties and relationships between warm partially ionized and hot and highly ionized gas in the local interstellar-medium (ISM). The majority of the measurements reviewed have been obtained through ultraviolet absorption spectroscopy recorded towards stellar targets located within ∼150 pc of the Sun. Many questions still remain to be answered concerning the location, temperature, density and source of ionization of both of these phases of the diffuse interstellar gas. In particular, we focus on absorption observations of the ions of C IV λ 1550 A and Si IV λ 1394 A and discuss if highly ionized gas (as traced by the O VI λ 1032 A ion) has in fact actually been detected within the Local Cavity.