The Antlia-Sextans Group is a small Galaxy group in the constellations Hydra , Sextans , Antlia and Leo . It is, on average, approximately 4.3 million light-years away from the Milky Way . It is generally considered to be at the very edge of the Local Group and thus part of it. However, other researchers indicate it is an independent Galaxy group, unlikely to be gravitationally bound to the Local Group due to probably lying outside the Local Group's Zero-velocity surface , and thus the nearest Galaxy group to the Local Group rather than a subgroup within the Local Group. Nonetheless—this possible independence may disappear as the Milky Way continues coalescing with Andromeda due to the increased mass, and density thereof, plausibly widening the radius of the Zero-velocity surface of the Local Group.
17-468: The Antlia-Sextans Group consists of the galaxies NGC 3109 , Sextans A , Sextans B , Antlia Dwarf , Leo P and Antlia B . Leo A might also belong to the group, but this is considered unlikely. NGC 3109 is the largest and dominant member of this group, with a diameter of 41,700 light-years, almost half the diameter of the Milky Way . It was the first discovered member of the group, discovered in 1835. It
34-659: A luminous blue variable , designated AT 2018akx (type LBV, mag. 17.5), was discovered on 22 March 2018. Magellanic spiral 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
51-472: A distance of 4.305 million light-years. The gas in the Antlia Dwarf galaxy has the same radial velocity as a warp in the disk of NGC 3109 , indicating that the two galaxies had a close encounter approximately one billion years ago. Sextans A is 7,990 light-years in diameter, and square-shaped, and contains numerous star clusters, located at the distance of about 4.658 million light-years away. Sextans A has
68-467: A massive globular cluster . Leo P (AGC 208583 ) is a small irregular galaxy discovered in 2013. It is only 0.4 Mpc from the Sextans B , so it is considered as a member of this grouping. It is the most distant member of all, with a distance of 5.3 million light years. Antlia B is recently discovered small galaxy. It is known to be a satellite of NGC 3109 situated at the distance of 1.35 ± 0.06 pc and
85-405: A peculiar square shape. Massive short-lived stars exploded in supernovae that caused more star formation, triggering yet more supernovae, ultimately resulting in an expanding shell. Young blue stars now highlight areas and shell edges high in current star formation, which from the perspective of observers on Earth appears roughly square. The 10.4m telescope Gran Telescopio Canarias recently observed
102-674: A substantial amount of dark matter . NGC 3109 is located about 1.33 megaparsecs (4.3 Mly) away, in the constellation Hydra . This puts it at the very outskirts of the Local Group . Its membership of the Local Group has been questioned, because it seems to be receding faster than estimates of the Local Group's escape velocity . It is distant enough from the largest members of the Local Group that it has not been tidally influenced by them. Although no supernovae have been observed in NGC 3109 yet,
119-457: A type of unbarred spiral galaxy , while SBm are a type of barred spiral galaxy . 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. dSm galaxies are dwarf spiral galaxies or dwarf irregular galaxies , depending on categorization scheme. The Magellanic spiral classification
136-537: A value of approximately Z = 0.001. Sextans B is receding from the Milky Way with a speed of approximately 300 kilometres per second (190 mi/s), and probably lies just outside the edge of the Local Group , so as its neighbour Sextans A . Five planetary nebulae have been identified in Sextans B, which is one of the smallest galaxies where planetary nebulae have been observed. These appear point-like and can be identified by their spectral emission lines. It also contains
153-490: Is also second closest to Earth, at a distance of 4.348 million light-years away. It was thought to be an irregular galaxy, but is now theorized to possibly be a barred spiral . It seems to be a galaxy with no central core. Based on spectroscopy of blue supergiants in NGC 3109, it is known that the galaxy has a low metallicity, similar to that to the Small Magellanic Cloud . It is one of the most metal-poor galaxies in
170-457: Is estimated to be about 2 × 10 times the mass of the Sun , of which 5.5 × 10 is in the form of atomic hydrogen . Star formation in the galaxy seems to have proceeded in distinct periods of low intensity, separated by shorter periods of no activity. The existence of Cepheid variables in the galaxy implies that Sextans B contains at least some young stars. The metallicity of Sextans B is rather low, with
187-413: Is in the form of neutral hydrogen . It is oriented edge-on from our point of view, and may contain a disk and a halo . The disk appears to be composed of stars of all ages, whereas the halo contains only very old and metal-poor stars. NGC 3109 does not appear to possess a galactic nucleus. From measurements of the neutral atomic hydrogen in the galaxy, it has been found that the disk of NGC 3109
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#1733085501186204-472: Is similar to the Antlia Dwarf in many ways. Antlia B is transitioning from an irregular galaxy to a dwarf spheroidal. It contains mainly metal poor old stars, although a small number of young blue stars (<1 Gyr) is present. The galaxy possesses a substantial (~300,000 solar masses) amount of neutral hydrogen but no outgoing star formation. NGC 3109 NGC 3109 is a small barred Magellanic type spiral or irregular galaxy around 4.35 Mly away in
221-577: Is warped. The warp has the same radial velocity as gas in the Antlia Dwarf galaxy, indicating that the two galaxies had a close encounter approximately one billion years ago. Based on spectroscopy of blue supergiants in NGC 3109, it is known that the galaxy has a low metallicity, similar to that to the Small Magellanic Cloud . It is one of the most metal-poor star-forming galaxies in the Local group. NGC 3109 seems to contain an unusually large number of planetary nebulae for its luminosity. It also contains
238-538: The B-band with an angular diameter of 1,980 arcseconds , it has an isophotal diameter approximately 12.80 kiloparsecs (41,700 light-years ) across, slightly larger than the Large Magellanic Cloud but smaller than the Triangulum Galaxy . If it is a spiral galaxy, it would be the smallest in the Local Group . NGC 3109 has a mass of about 2.3 × 10 times the mass of the Sun ( M ☉ ), of which 20%
255-411: The Local group, if it is included. NGC 3109 seems to contain an unusually large number of planetary nebulae for its luminosity. It also contains a substantial amount of dark matter . From measurements of the neutral atomic hydrogen in the galaxy, it has been found that the disk of NGC 3109 is warped. Antlia Dwarf is the smallest and closest galaxy in the group, only 2,610 light-years in diameter at
272-479: The OB-type stars that power the giant HII regions. Sextans A have formed a pair with the most remote galaxy in the group, Sextans B . Sextans B is the second largest galaxy in the group, with a diameter of 8,900 light-years. Sextans B is the most distant from Earth in the group, at 5.101 million light-years away. Sextans B has a uniform stellar population, but the interstellar medium in it may be inhomogeneous. Its mass
289-400: The direction of the constellation of Hydra . NGC 3109 is believed to be tidally interacting with the dwarf elliptical galaxy Antlia Dwarf . It was discovered by John Herschel on March 24, 1835 while he was in what is now South Africa . NGC 3109 is classified as a Magellanic type irregular galaxy , but it may in fact be a small spiral galaxy . Based on the D 25.5 isophote at
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