Recent observational studies on carbon-chain species with current facilities and future prospects with ALMA & JWST

Carbon-chain species have been widely found in star-forming regions and are considered to form via a bottom-up mechanism in which ionic and atomic carbon (C⁺ and C) play essential roles. Recent deep line survey observations toward the Cyanpolyyne Peak in Taurus Molecular Cloud-1 (hereafter TMC-1 CP) have achieved the discovery of new carbon-bearing species; e.g., large hydrocarbon rings and species including benzene rings such as cyanobenzene, cyanonaphthalene, and cyanopyrene. The bottom-up mechanism cannot explain their presence and now we need to revisit the carbon chemistry in the interstellar medium (ISM). One possible approach is to explore the carbon chemistry from evolved stars where carbon is ejected into the ISM through the diffuse ISM to the next-generation star-forming regions, or molecular clouds. Combining ALMA and JWST, we will be able to explore carbon chemistry including top-down mechanisms.