Antlia Dwarf
Encyclopedia
The Antlia Dwarf is a dwarf spheroidal
/irregular galaxy
. It lies about 1.3 Mpc (4.3 Mly
) from Earth in the constellation Antlia
. It is the fourth and faintest member of the nearby Antlia 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
, NGC 3109
.
, and A. de Vaucouleurs. Later in 1985 and 1987 it was noted as 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).
In 1999 Antlia Dwarf was identified by Sidney van den Bergh
as the fourth member of the Antlia Group—the group of galaxies closest to the Local Group
.
of type dE3.5, or either as a dwarf spheroidal galaxy
(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 a old halo. Its half-light radius is about 0.25 Kpc. The metallicity
is very low, at about<[Fe/H]> =−1.6 to −1.9 meaning that Antlia Dwarf contains 40–80 times less heavy elements than the Sun. The galaxy has a well-defined and easily observed red giant branch, which makes measuring its distance relatively easy. The total luminosity of Antlia Dwarf is approximately 1 million that of the Sun (the visible absolute magnitude is MV=−10.3).
The stellar mass of Antlia Dwarf is estimated to be about 2–4×106 solar mass
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
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 solar mass
es) of neutral atomic hydrogen
. However it does not have significant H II region
s and does not actively form stars at the present moment.
. Its distance from the barycenter 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 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 29 kpc to 180 kpc 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.
Dwarf spheroidal galaxy
Dwarf spheroidal galaxy is a term in astronomy applied to low luminosity galaxies that are companions to the Milky Way and to the similar systems that are companions to the Andromeda Galaxy M31...
/irregular galaxy
Irregular galaxy
An irregular galaxy is a galaxy that does not have a distinct regular shape, like a spiral or an elliptical galaxy. The shape of an irregular galaxy is uncommon – they do not fall into any of the regular classes of the Hubble sequence, and they are often chaotic in appearance, with neither a...
. It lies about 1.3 Mpc (4.3 Mly
Light-year
A light-year, also light year or lightyear is a unit of length, equal to just under 10 trillion kilometres...
) from Earth in the constellation Antlia
Antlia
Antlia is a constellation in the southern sky. Its name means "pump" and it specifically represents an air pump. The stars comprising Antlia are faint, and the constellation was not created until the 18th century...
. It is the fourth and faintest member of the nearby Antlia 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
Barred spiral galaxy
A barred spiral galaxy is a spiral galaxy with a central bar-shaped structure composed of stars. Bars are found in approximately two-thirds of all spiral galaxies...
, NGC 3109
NGC 3109
NGC 3109 is a small spiral or irregular galaxy around 4.2 Mly away in the direction of the constellation of Hydra. It is the most prominent member of a Local Group subgroup. NGC 3109 is believed to be tidally interacting with the dwarf elliptical galaxy, Antlia Dwarf...
.
Discovery
Antlia Dwarf was first cataloged in 1985 by H. Corwin, Gérard de VaucouleursGérard de Vaucouleurs
-External links:* * http://nedwww.ipac.caltech.edu/level5/normal_galaxies.html-Other resources:...
, and A. de Vaucouleurs. Later in 1985 and 1987 it was noted as 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
Mike Irwin
Michael Irwin is director of the Cambridge Astronomical Survey Unit and one of the discoverers of the Cetus Dwarf galaxy and the Sagittarius Dwarf Elliptical Galaxy.-References:...
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).
In 1999 Antlia Dwarf was identified by Sidney van den Bergh
Sidney van den Bergh
Sidney Van den Bergh, OC, FRS is a retired Canadian astronomer.Born in the Netherlands, son of businessman and politician Sidney James van den Bergh and grandson of Unilever co-founder Samuel van den Bergh, he showed an interest in science from an early age, learning to read with books on astronomy...
as the fourth member of the Antlia Group—the group of galaxies closest to the Local Group
Local Group
The Local Group is the group of galaxies that includes Earth's galaxy, the Milky Way. The group comprises more than 30 galaxies , with its gravitational center located somewhere between the Milky Way and the Andromeda Galaxy...
.
Properties
The Antlia Dwarf is classified alternatively as a dwarf elliptical galaxyDwarf elliptical galaxy
Dwarf elliptical galaxies, or dEs, are elliptical galaxies that are much smaller than others. They are classified as dE, and are quite common in galaxy groups and clusters, and are usually companions to other galaxies.- Examples :...
of type dE3.5, or either as a dwarf spheroidal galaxy
Dwarf spheroidal galaxy
Dwarf spheroidal galaxy is a term in astronomy applied to low luminosity galaxies that are companions to the Milky Way and to the similar systems that are companions to the Andromeda Galaxy M31...
(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 a old halo. Its half-light radius is about 0.25 Kpc. The metallicity
Metallicity
In astronomy and physical cosmology, the metallicity of an object is the proportion of its matter made up of chemical elements other than hydrogen and helium...
is very low, at about
The stellar mass of Antlia Dwarf is estimated to be about 2–4×106 solar mass
Solar mass
The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...
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
Star formation is the process by which dense parts of molecular clouds collapse into a ball of plasma to form a star. As a branch of astronomy star formation includes the study of the interstellar medium and giant molecular clouds as precursors to the star formation process and the study of young...
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 solar mass
Solar mass
The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...
es) of neutral atomic hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
. However it does not have significant H II region
H II region
An H II region is a large, low-density cloud of partially ionized gas in which star formation has recently taken place. The short-lived, blue stars forged in these regions emit copious amounts of ultraviolet light, ionizing the surrounding gas...
s and does not actively form stars at the present moment.
Location and interactions
The Antlia Dwarf is located about 1.31 Mpc away, in the constellation AntliaAntlia
Antlia is a constellation in the southern sky. Its name means "pump" and it specifically represents an air pump. The stars comprising Antlia are faint, and the constellation was not created until the 18th century...
. Its distance from the barycenter of the Local Group is about 1.7 Mpc. At this distance, it is situated well outside the Local Group
Local Group
The Local Group is the group of galaxies that includes Earth's galaxy, the Milky Way. The group comprises more than 30 galaxies , with its gravitational center located somewhere between the Milky Way and the Andromeda Galaxy...
and is a member of a separate group of dwarf galaxies called Antlia Group. The Antlia Dwarf is separated from the small spiral/irregular galaxy NGC 3109
NGC 3109
NGC 3109 is a small spiral or irregular galaxy around 4.2 Mly away in the direction of the constellation of Hydra. It is the most prominent member of a Local Group subgroup. NGC 3109 is believed to be tidally interacting with the dwarf elliptical galaxy, Antlia Dwarf...
by only 1.18 degrees on the sky, which corresponds to a physical separation of 29 kpc to 180 kpc 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.