Gasmassen

Gasmassen is a term used in Nordic-language astronomy literature to denote the total mass of gas contained in a given object or region, such as a galaxy, a molecular cloud, or the intracluster medium. It is a key component of the baryonic mass budget and is distinct from the mass in stars or dark matter. In English-language practice, the quantity is usually called gas mass, and is commonly abbreviated M_gas. Gasmassen can be subdivided into atomic gas (M_HI) and molecular gas (M_H2), depending on the tracers employed.

Gas mass is inferred from spectral line observations and dust measurements. The 21-centimeter line of neutral hydrogen (HI) provides a direct measure of atomic gas, while the CO rotational lines serve as tracers of molecular hydrogen (H2) with a conversion factor X_CO. Dust continuum emission, together with an assumed gas-to-dust ratio, offers another route. In some cases, dynamical modeling of gas kinematics or hydrostatic equilibrium is used to constrain M_gas.

Typical gas masses in disc galaxies range from about 10^8 to a few times 10^10 solar masses, with gas fractions from a few to a few tens of percent. In galaxy clusters, the intracluster medium contains gas masses on the order of 10^13 to 10^14 solar masses. Gas mass is central to studies of star formation, galaxy evolution, and gas accretion processes.

See also: interstellar medium, molecular clouds, atomic hydrogen (HI), carbon monoxide (CO) as a tracer, gas-to-dust ratio, baryonic mass, star formation efficiency.