| Wolf-Lundmark-Melotte Galaxy | |
|---|---|
Wolf-Lundmark-Melotte galaxy. |
|
| Observation data (J2000 epoch) | |
| Constellation | Cetus |
| Right ascension | 00h 01m 58.1s[1] |
| Declination | -15° 27′ 39″[1] |
| Redshift | -122 ± 2 km/s[1] |
| Distance | 3.04 ± 0.11 Mly (930 ± 30 kpc)[2] |
| Type | IB(s)m[1] |
| Apparent dimensions (V) | 11′.5 × 4′.2[1] |
| Apparent magnitude (V) | 11.0[1] |
| Notable features | - |
| Other designations | |
| WLM,[1] DDO 221,[1] UGCA 444,[1] PGC 143[1] | |
| See also: Galaxy, List of galaxies | |
The Wolf-Lundmark-Melotte (WLM) galaxy is an irregular galaxy discovered in 1909 by Max Wolf, and is 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.
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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 burst that started ~13 Gyr ago. During the burst, 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.[3]
WLM has one known globular cluster that Hodge et al. (1999) determined has Mv = -8.8 and [Fe/H] = -1.5 with an age of ~15 Gyr. This cluster has a luminosity that is slightly over the average for all globulars. The seeming lack of faint low-mass globular clusters can not be explained by the weak tidal forces of the WLM system.[3]
In E.E. Smith’s Lensman novels, the "Second Galaxy" is identified as “Lundmark’s Nebula.”[4] 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; obviously, this is the galaxy that E.E. Smith was thinking of when he wrote the series. At the time the Lensman series was written, most astronomers favored the tidal theory of solar system formation, which required that planets be formed by the close approach of another star. In order to produce the massive numbers of planets necessary to evolve into the galactic civilizations in both our Galaxy and Lundmark's Nebula portrayed in the Lensman series, E.E. Smith felt it would have been necessary for another galaxy to have passed through our galaxy in the past to produce the large number of close encounters necessary to form so many planets.