Wolf-Lundmark-Melotte Galaxy
| Wolf–Lundmark–Melotte | |
|---|---|
The galaxy Wolf–Lundmark–Melotte (WLM), imaged by VLT
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| Observation data (J2000 epoch) | |
| Constellation | Cetus |
| Right ascension | 00h 01m 58.1s |
| Declination | −15° 27′ 39″ |
| Redshift | -122 ± 2 km/s |
| Distance | 3.04 ± 0.11 Mly (930 ± 30 kpc) |
| Apparent magnitude (V) | 11.0 |
| Characteristics | |
| Type | IB(s)m |
| Apparent size (V) | 11′.5 × 4′.2 |
| Notable features | - |
| Other designations | |
| WLM,DDO 221, UGCA 444,PGC 143 | |
The Wolf–Lundmark–Melotte (WLM) is an 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 in the constellation Cetus.
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 [Fe/H] ~ −2.2 to [Fe/H] −1.3. There being no horizontal-branch population, Dolphin concludes that no more than ~20 M☉ 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 200 M☉ 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 has one known globular cluster (PGC 910901) at 00h 01m 29.5s −15° 27′ 51″ that Hodge et al. (1999) determined having an absolute magnitude of −8.8 and a metallicity of –1.5, with an age of ~15 billion years. This cluster has a luminosity that is slightly over the average for all globulars. The seeming lack of faint low-mass globular clusters cannot be explained by the weak tidal forces of the WLM system.
In E. E. Smith’s Lensman novels, the "Second Galaxy" is identified as "Lundmark's Nebula". However, some believe the "Second Galaxy" may not be the Wolf–Lundmark–Melotte galaxy, since the first chapter of the first novel in the series (Triplanetary) and the series-establishing material appearing at the beginning of subsequent novels states that the "Second Galaxy" and the "First Galaxy" (the Milky Way) collided and passed through each other "edge-on" during the "planet-forming era"—implying that the "Lundmark's Nebula" of the series must necessarily be obscured from view by the Milky Way; however, according to others, it could have passed through at an angle and thus be identified with the galaxy described in this article; some have stated that this is the galaxy that E.E. Smith was thinking of when he wrote the series. However, the distance to Lundmark's nebula is defined quite precisely in Grey Lensman and is much larger than the distance to Wolf–Lundmark–Melotte (approximately ten times greater). Additionally, in Second Stage Lensmen multiple references are made to the spiral arms of Lundmark's Nebula. Wolf–Lundmark–Melotte does not possess such structures. At the time of writing of these books, the name of Lundmark was associated with such classifications and Smith may have elected to use this as a "believable" name for an entirely fictional galaxy.
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