NGC 3109
Encyclopedia
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
. It was discovered by John Herschel
on March 24, 1835 while he was in South Africa
.
type irregular galaxy
, but it may in fact be a small spiral galaxy
. If it is a spiral galaxy, it would be the smallest in the Local Group.
NGC 3109 has a mass of about 2.3×109 times the mass of the Sun
, of which 20% 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 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.
. It is one of the most metal-poor galaxies in the Local group.
NGC 3109 seems to contain an unusually large number of planetary nebula
e for its luminosity. It also contains a substantial amount of dark matter
.
. This puts it at the very outskirts of the Local Group
. Its membership of the Local Group has been challenged, 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.
Spiral galaxy
A spiral galaxy is a certain kind of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae and, as such, forms part of the Hubble sequence. Spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as...
or 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...
around 4.2 Mly away in the direction of the constellation of Hydra
Hydra (constellation)
Hydra is the largest of the 88 modern constellations, measuring 1303 square degrees. It has a long history, having been included among the 48 constellations listed by the 2nd century astronomer Ptolemy. It is commonly represented as a water snake...
. It is the most prominent member of a 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...
subgroup. NGC 3109 is believed to be tidally interacting
Galactic tide
A galactic tide is a tidal force experienced by objects subject to the gravitational field of a galaxy such as the Milky Way. Particular areas of interest concerning galactic tides include galactic collisions, the disruption of dwarf or satellite galaxies, and the Milky Way's tidal effect on the...
with the dwarf elliptical galaxy
Dwarf 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 :...
, Antlia Dwarf
Antlia Dwarf
The Antlia Dwarf is a dwarf spheroidal/irregular galaxy. It lies about 1.3 Mpc 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...
. It was discovered by John Herschel
John Herschel
Sir John Frederick William Herschel, 1st Baronet KH, FRS ,was an English mathematician, astronomer, chemist, and experimental photographer/inventor, who in some years also did valuable botanical work...
on March 24, 1835 while he was in South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
.
Size and morphology
NGC 3109 is classified as a MagellanicMagellanic Clouds
The two Magellanic Clouds are irregular dwarf galaxies visible in the southern hemisphere, which are members of our Local Group and are orbiting our Milky Way galaxy...
type 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...
, but it may in fact be a small spiral galaxy
Spiral galaxy
A spiral galaxy is a certain kind of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae and, as such, forms part of the Hubble sequence. Spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as...
. If it is a spiral galaxy, it would be the smallest in the Local Group.
NGC 3109 has a mass of about 2.3×109 times the mass of the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
, of which 20% is in the form of neutral 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...
. It is oriented edge-on from our point of view, and may contain a disk
Disc (galaxy)
A disc is a component of disc galaxies, such as spiral galaxies, or lenticular galaxies.The galactic disc is the plane in which the spirals, bars and discs of disc galaxies exist. Galaxy discs tend to have more gas and dust, and younger stars than galactic bulges, or galactic haloes.The galactic...
and a halo
Galactic halo
The term galactic halo is used to denote an extended, roughly spherical component of a galaxy, which extends beyond the main, visible component. It can refer to any of several distinct components which share these properties:* the galactic spheroid...
. The disk appears to be composed of stars of all ages, whereas the halo contains only very old and metal-poor
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...
stars. NGC 3109 does not appear to possess a galactic nucleus.
From measurements of the 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...
in the galaxy, it has been found that the disk of NGC 3109 is warped. The warp has the same radial velocity
Radial velocity
Radial velocity is the velocity of an object in the direction of the line of sight . In astronomy, radial velocity most commonly refers to the spectroscopic radial velocity...
as gas in the Antlia Dwarf
Antlia Dwarf
The Antlia Dwarf is a dwarf spheroidal/irregular galaxy. It lies about 1.3 Mpc 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...
galaxy, indicating that the two galaxies had a close encounter approximately one billion years ago.
Composition
Based on spectroscopy of red giants in NGC 3109, it is known that the galaxy has a low metallicity, similar to that to the Small Magellanic CloudSmall Magellanic Cloud
The Small Magellanic Cloud is a dwarf galaxy. It has a diameter of about 7,000 light-years and contains several hundred million stars. It has a total mass of approximately 7 billion times the mass of our Sun....
. It is one of the most metal-poor galaxies in the Local group.
NGC 3109 seems to contain an unusually large number of planetary nebula
Planetary nebula
A planetary nebula is an emission nebula consisting of an expanding glowing shell of ionized gas ejected during the asymptotic giant branch phase of certain types of stars late in their life...
e for its luminosity. It also contains a substantial amount of dark matter
Dark matter
In astronomy and cosmology, dark matter is matter that neither emits nor scatters light or other electromagnetic radiation, and so cannot be directly detected via optical or radio astronomy...
.
Location
NGC 3109 is located about 1.3 Mpc away, in the constellation HydraHydra (constellation)
Hydra is the largest of the 88 modern constellations, measuring 1303 square degrees. It has a long history, having been included among the 48 constellations listed by the 2nd century astronomer Ptolemy. It is commonly represented as a water snake...
. This puts it at the very outskirts of 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...
. Its membership of the Local Group has been challenged, because it seems to be receding faster than estimates of the Local Group's escape velocity
Escape velocity
In physics, escape velocity is the speed at which the kinetic energy plus the gravitational potential energy of an object is zero gravitational potential energy is negative since gravity is an attractive force and the potential is defined to be zero at infinity...
. It is distant enough from the largest members of the Local Group that it has not been tidally influenced by them.