galaxyscale

Galaxyscale is a term used in astronomy and astrophysics to describe the characteristic physical scale associated with a galaxy. It encompasses the spatial extent of the stellar component, the distribution of gas and dark matter within the galaxy, and the range of processes that operate on galactic dimensions. The term is descriptive rather than a formal quantity, and it is used to discuss phenomena that span an entire galaxy or its immediate halo.

Observationally, galaxyscale is tied to measurable quantities such as the effective radius (R_e), the disk scale length, and the virial radius of the surrounding dark matter halo (R_200). Disk-dominated galaxies typically have R_e of a few kiloparsecs, while giant ellipticals can have R_e tens of kiloparsecs. The virial radius of Milky Way–like halos is of order 200 kiloparsecs. The overall luminous diameter of a galaxy is commonly tens of kiloparsecs across.

In theory, galaxyscale relates to hierarchical structure formation, the balance of baryons and dark matter within halos, and the regulation of star formation by feedback. Galaxy scaling relations, such as the Tully–Fisher relation and the Fundamental Plane, connect galaxyscale properties to dynamical mass and luminosity and provide constraints on formation models.

In simulations, galaxyscale refers to the resolution at which galactic structure and subgrid physics are modeled. Models must capture processes from star-forming clumps on sub-kiloparsec scales up to the halo boundary at hundreds of kiloparsecs.

Examples commonly discussed under galaxyscale include the Milky Way, Andromeda (M31), and other disk and elliptical galaxies that illustrate the diversity of galactic sizes and mass distributions.