Interstellar and intergalactic medium in the ultraviolet band
This article presents an overview of key scientific challenges in the astrophysics and astrochemistry of the interstellar and intergalactic media. Addressing many of these challenges will become possible with the Russian space observatory Spektr-UF, which is currently being prepared for launch. The ultraviolet (UV) spectral range is critically important for studying the evolution of the Universe, as it contains fundamental absorption and emission lines of most chemical elements and the most important molecules. These lines make it possible to reliably determine the physical conditions and chemical composition of various astrophysical objects, as well as the characteristics of the processes occurring within them. The article examines the prospects for UV observations across a broad range of scientific problems, from investigating the epoch of helium reionization and the thermal history of the Universe to mapping ongoing star formation in galaxies. Dedicated sections address the study of the chemical evolution of galaxies at intermediate redshifts, the distribution of "hidden" baryons and metals, the small-scale structure of interstellar clouds, the physics of photodissociation regions and protoplanetary disks, and the modeling of UV emission from nebulae surrounding fast-moving pulsars. The high sensitivity and spectral resolution of the Spektr-UF instruments are expected to provide fundamentally new data across all these research areas, filling existing gaps in our understanding of the interstellar and intergalactic media.