A Magellanic spiral galaxy is a spiral galaxy with only one spiral arm. Magellanic spiral galaxies are classified as the type Sm (with sub-categories SAm, SBm, SABm); the prototype galaxy and namesake for Magellanic spirals is the Large Magellanic Cloud, an SBm galaxy. They are usually smaller dwarf galaxies and can be considered to be intermediate between dwarf spiral galaxies and irregular galaxies.
SAm galaxies are a type of unbarred spiral galaxy, while SBm are a type of barred spiral galaxy.[1] SABm are a type of intermediate spiral galaxy.
Type Sm and Im galaxies have also been categorized as irregular galaxies with some structure (type Irr-1). Sm galaxies are typically disrupted and asymmetric.[2] dSm galaxies are dwarf spiral galaxies or dwarf irregular galaxies, depending on categorization scheme.
The Magellanic spiral classification was introduced by Gerard de Vaucouleurs, along with Magellanic irregular (Im), when he revamped the Hubble classification of galaxies.
| Example | Type | Image | Information and Notes | |
|---|---|---|---|---|
| Magellanic Spirals | ||||
| SAdm | ||||
| NGC 5204 | SAm | Satellite of Pinwheel Galaxy | ||
| NGC 4676A | SABdm | Part of a galaxy merger, to the left of it is the galaxy NGC 4676B. | ||
| NGC 4625 | SABm | It has only one spiral arm. In ultraviolet it extends four times farther than in visible light. | ||
| NGC 4236 | SBdm | In M81 Group | ||
| Large Magellanic Cloud | SBm | Prototype galaxy for this galaxy class, and satellite of Milky Way | ||
| Sdm | ||||
| Sm | ||||
| Dwarf Magellanic Spirals | ||||
| dSAdm | ||||
| dSAm | ||||
| dSABdm | ||||
| dSABm | ||||
| dSBdm | ||||
| dSBm | ||||
| dSdm | ||||
| NGC 5474 | dSm | Satellite of Pinwheel Galaxy |