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An Irr-II galaxy ( Irr II) is an irregular galaxy that does not appear to feature any structure that can place it into the Hubble sequence. A dI-galaxy (or dIrr) is a dwarf irregular galaxy. [7] This type of galaxy is now thought to be important to understand the overall evolution of galaxies, as they tend to have a low level of metallicity and ...
Tully–Fisher relation. In astronomy, the Tully–Fisher relation ( TFR) is a widely verified empirical relationship between the mass or intrinsic luminosity of a spiral galaxy and its asymptotic rotation velocity or emission line width. Since the observed brightness of a galaxy is distance-dependent, the relationship can be used to estimate ...
Galaxy morphological classification is a system used by astronomers to divide galaxies into groups based on their visual appearance. There are several schemes in use by which galaxies can be classified according to their morphologies, the most famous being the Hubble sequence , devised by Edwin Hubble and later expanded by Gérard de ...
Peculiar galaxy. ESO 162-17 is an example of a peculiar galaxy which is 40 million light-years away in the constellation Carina. A peculiar galaxy is a galaxy of unusual size, shape, or composition. [1] Between five and ten percent of known galaxies are categorized as peculiar. [2] Astronomers have identified two types of peculiar galaxies ...
The Mice Galaxies (NGC 4676 A&B) are in the process of merging. This artist's impression shows the merger between two galaxies leading to the formation of a disc galaxy. Galaxy mergers can occur when two (or more) galaxies collide. They are the most violent type of galaxy interaction. The gravitational interactions between galaxies and the ...
The Atlas of Peculiar Galaxies is a catalog of peculiar galaxies produced by Halton Arp in 1966. A total of 338 galaxies are presented in the atlas, which was originally published in 1966 by the California Institute of Technology. The primary goal of the catalog was to present photographs of examples of the different kinds of peculiar ...
In irregular galaxies, open clusters may be found throughout the galaxy, although their concentration is highest where the gas density is highest. Open clusters are not seen in elliptical galaxies: Star formation ceased many millions of years ago in ellipticals, and so the open clusters which were originally present have long since dispersed.
NGC 1427A is an irregular galaxy in the constellation Eridanus. Its distance modulus has been estimated using the globular cluster luminosity function to be 31.01 ± 0.21 which is about 52 Mly. It is the brightest dwarf irregular member of the Fornax cluster and is in the foreground of the cluster's central galaxy NGC 1399.