Wolf–Lundmark–Melotte
The Wolf–Lundmark–Melotte Galaxy is a barred irregular galaxy discovered in 1909 by Max Wolf, located on the outer edges of the Local Group. The discovery of the nature of the galaxy was accredited to Knut Lundmark and Philibert Jacques Melotte in 1926. It is located in the constellation of Cetus.
Properties
Wolf–Lundmark–Melotte is a rotating disk that is seen edge-on. It is relatively isolated from the rest of the Local Group, and does not seem to show much evidence of interaction. However, the rotation curve of Wolf–Lundmark–Melotte is asymmetrical, in that the receding side and approaching side of the galaxy are rotating in different ways.Although isolated, Wolf–Lundmark–Melotte shows evidence of ram pressure stripping. It is far outside of the virial radius of the Milky Way, so it is possible that Wolf–Lundmark–Melotte is currently passing through some relatively dense medium.
Star formation
In 1994, A. E. Dolphin used the Hubble Space Telescope to create a color–magnitude diagram for WLM. It showed that around half of all the star formation in this galaxy occurred during a starburst that started ~13 Gyr ago. During the starburst, the metallicity of WLM rose from ~ −2.2 to −1.3. There being no horizontal-branch population, Dolphin concludes that no more than per Myr of star formation occurred in the period from 12 to 15 Gyr ago. From 2.5 to 9 Gyr ago, the mean rate of star formation was 100 to per Myr. Being at the edge of the Local Group has also protected WLM from interactions and mergers with other galaxies, giving it a "pristine" stellar population and state that make it particularly useful for comparative studies.WLM is currently forming stars, as evidenced by clumps of newly formed stars visible in ultraviolet light. These clumps are about 20 to 100 light-years in size. The youngest clumps are found in the southern half of the galaxy, which has more star formation.
In 2015, interferometric observations from ALMA detected CO in the low metallicity dwarf galaxy WLM revealed dense cloud cores. These results suggest that the CO clouds in WLM are normal in terms of density, pressure and column density, which explains why they lie on the standard correlations. They also appear to be marginally self-bound by gravity, suggesting that they are related to star formation. Their properties are typical for parsec-size molecular cloud cores in the solar neighbourhood.