The Antlia Dwarf is a dwarf spheroidal/

irregular galaxy An irregular galaxy is a galaxy that does not have a distinct regular shape, unlike a spiral or an elliptical galaxy. Irregular galaxies do not fall into any of the regular classes of the Hubble sequence, and they are often chaotic in appearan ...

. It lies about 1.3 Mpc (4.3 million

light-year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astr ...

s) from

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

in the constellation

Antlia Antlia (; from Ancient Greek ''ἀντλία'') is a constellation in the Southern Celestial Hemisphere. Its name means "pump" in Latin and Greek language, Greek; it represents an air pump. Originally Antlia Pneumatica, the constellation was es ...

. It is the fourth and faintest member of the nearby Antlia-Sextans Group of galaxies. The galaxy contains stars of all ages, contains significant amounts of gas, and has experienced recent star formation. The Antlia Dwarf is believed to be tidally interacting with the small

barred spiral galaxy A barred spiral galaxy is a spiral galaxy with a central bar-shaped structure composed of stars. Bars are found in about two thirds of all spiral galaxies in the local universe, and generally affect both the motions of stars and interstellar gas ...

NGC 3109.

Discovery

The Antlia Dwarf was first cataloged in 1985 by H. Corwin, Gérard de Vaucouleurs, and A. de Vaucouleurs. Later in 1985 and 1987, it was noted as a possible nearby dwarf galaxy by two groups of astronomers. It was finally confirmed as a dwarf galaxy in 1997 by Alan Whiting, Mike Irwin and George Hau during a survey of the northern sky. They for the first time resolved it into stars and determined the distance to it—1.15 Mpc (the modern distance estimate is slightly larger). The same year, Antonio Aparicio, Julianne Dalcanton, Carme Gallart and David Martinez-Delgado studied for the first time its stellar content and measured its mass, luminosity and metallicity. In 1999, the Antlia Dwarf was identified by Sidney van den Bergh as the fourth member of the Antlia-Sextans Group—the group of galaxies closest to the Local Group.

Properties

The Antlia Dwarf is classified alternatively as a dwarf elliptical galaxy of type dE3.5, or either as a

dwarf spheroidal galaxy A dwarf spheroidal galaxy (dSph) is a term in astronomy applied to small, low-luminosity galaxies with very little dust and an older stellar population. They are found in the Local Group as companions to the Milky Way and as systems that are c ...

(dSph) or as a transitional galaxy from spheroidal to irregular types (dSph/Irr). The last classification is due to a substantial star formation in this galaxy in the last 0.1 billion years. Antlia Dwarf comprises two components: a core and an old halo. Its half-light radius is about 0.25 kpc. The

metallicity In astronomy, metallicity is the Abundance of the chemical elements, abundance of Chemical element, elements present in an object that are heavier than hydrogen and helium. Most of the normal currently detectable (i.e. non-Dark matter, dark) matt ...

is very low, at about < e/H=−1.6 to −1.9 meaning that Antlia Dwarf contains 40–80 times less heavy elements than the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

. The galaxy has a well-defined and easily observed

red giant branch The red-giant branch (RGB), sometimes called the first giant branch, is the portion of the giant branch before helium ignition occurs in the course of stellar evolution. It is a stage that follows the main sequence for low- to intermediate-mass st ...

, which makes measuring its distance relatively easy. The total luminosity of Antlia Dwarf is approximately 1 million times that of the Sun (the visible absolute magnitude is M_V=−10.3). The stellar mass of Antlia Dwarf is estimated to be about 2–4 million

solar mass The solar mass () is a frequently used unit of mass in astronomy, equal to approximately . It is approximately equal to the mass of the Sun. It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxie ...

es, while its total mass (within the visible radius) is approximately 4 solar masses. The galaxy contains stars of all ages but is dominated by old stars with the age of more than 10 billion year. There seems to have been a major episode of

star formation Star formation is the process by which dense regions within molecular clouds in interstellar space—sometimes referred to as "stellar nurseries" or "star-forming regions"—Jeans instability, collapse and form stars. As a branch of astronomy, sta ...

in the Antlia Dwarf around 100 million years ago. However, the young stars are confined to the central core of the galaxy. Antlia Dwarf is unusual among dwarf spheroidal galaxies in that it contains large amounts (as much as 7 ×10⁵

es) of neutral atomic

hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

. However it does not have significant H II regions and does not actively form stars at the present moment.

Location and interactions

The Antlia Dwarf is located about away, in the constellation

. Its distance from the

barycenter In astronomy, the barycenter (or barycentre; ) is the center of mass of two or more bodies that orbit one another and is the point about which the bodies orbit. A barycenter is a dynamical point, not a physical object. It is an important con ...

of the Local Group is about 1.7 Mpc. At this distance, it is situated well outside the Local Group and is a member of a separate group of dwarf galaxies called Antlia-Sextans Group. The Antlia Dwarf is separated from the small spiral/irregular galaxy NGC 3109 by only 1.18 degrees on the sky, which corresponds to a physical separation of to depending on their radial separation. The Antlia Dwarf and NGC 3109 may be actually physically bound if the distance between them is not very large. However their velocity relative to each other—43 km/s makes it questionable whether they are in fact a bound system, especially if the distance between them is closer to the upper limit—180 kpc. If they are gravitationally bound, their total mass may be as high as 78 billion solar masses. Observations have also demonstrated that NGC 3109 has a warp in its gaseous disk that is traveling at the same velocity as the gas in the Antlia Dwarf, indicating that the two galaxies had a close encounter about one billion years ago.

References

External links

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Antlia Dwarf at Constellation Guide
{{DEFAULTSORT:Antlia Dwarf Dwarf elliptical galaxies Antlia 029194 NGC 3109 subgroup