Dwarf Galaxy at the Pump

The dwarf galaxy in Pump in 1985 was included in the catalog of H. Corvin, J. de Vaucouleur and A de Vaucouleur. Later in 1985 and 1987, two groups of astronomers suggested that the object was a nearby dwarf galaxy . ^[3] Finally, the galaxy was classified as a dwarf galaxy in 1997 by Alan Whiting, Mike Irwin and George Howe as part of a review of the northern sky. Scientists for the first time resolved the galaxy into individual stars and determined the distance to it - 1.15 Mpc (the current estimate is slightly larger). ^[eight]

In 1999, Sydney van den Berg classified the dwarf galaxy at Pump as the fourth representative of the galaxy group at Pump, the closest galaxy group relative to the Local Group . ^[3]

The dwarf galaxy in the Pump is also attributed to dwarf elliptical galaxies of the dE3.5 type ^{[8] [9]} or to dwarf spheroidal galaxies (dSph), and sometimes to the transitional type between spheroidal and irregular galaxies (dSph / Irr). ^[3] The last classification variant arose as a result of star formation occurring in the last 0.1 billion years.

The dwarf galaxy in the Pump consists of two components: the core and the old halo. ^[2] The effective radius is about 0.25 kpc. ^[8] Metallicity is very low, of the order of <[Fe / H]> = –1.6 to −1.9, that is, the galaxy on average contains 40–80 times less heavy elements than the Sun. ^{[2] [10]} A well-defined branch of red giants is observed in the galaxy, due to which it is possible to reliably determine the distance to the galaxy. ^{[9] The} total luminosity of the galaxy is approximately a million times higher than the luminosity of the Sun ( absolute magnitude in the visible range M _V = −10.3). ^[2]

The mass of the stellar component of the dwarf galaxy in the Pump is estimated to be 2–4 × 10 ⁶ solar masses, and the total mass (within the observed radius) is 4 × 10 ⁷ solar masses. ^{[2] The} galaxy contains stars of all ages, but most of the stars are old, with an age of more than 10 billion years. Probably about 100 million years ago, a starburst occurred in the galaxy. ^{[4] [9]} However, young stars are mainly located in the core of the galaxy. ^[ten]

The dwarf galaxy in the Pump is unusual among other dwarf spheroidal galaxies in that it contains a large amount (about 7 × 10 ⁵ solar masses) of neutral atomic hydrogen. ^{[11] [12]} However, it does not have large H II regions and does not show signs of active star formation at the moment. ^[9]

The dwarf galaxy in the Pump is located at a distance of 1.31 Mpc from the Sun in the constellation Pump. ^[9] The distance to the baricenter of the Local Group is 1.7 Mpc. At this distance, the galaxy is outside the Local Group and is part of a separate group of dwarf galaxies called the Pump galaxy group. ^{[3] The} galaxy is separated from the small spiral / irregular galaxy NGC 3109 on the Earth’s sky by an angular distance of 1.18 degrees, which corresponds to a linear distance of 29 to 180 kpc depending on the distance along the line of sight. ^{[3] [2]}

The dwarf galaxy in Pump and NGC 3109 can be physically connected if the distance between them is not too large. ^{[3] [8]} However, their speeds relative to each other are 43 km / s, ^[3] which casts doubt on the possibility of galaxies belonging to a close system, especially if the distance between them is close to the upper estimate of 180 kpc. ^{[2] [9]} If the galaxies are gravitationally bound, then their total mass can reach 78 million solar masses. ^[four]

Observations show that NGC 3109 has a gas-disk bend moving at a gas velocity in a dwarf galaxy in the Pump; this indicates the close rapprochement of galaxies that occurred about a billion years ago. ^[12]

• Antlia Dwarf at Constellation Guide