Andromeda IV (And IV) is an isolated irregular dwarf galaxy. The moderate
surface brightness
In astronomy, surface brightness (SB) quantifies the apparent brightness or flux density per unit angular area of a spatially extended object such as a galaxy or nebula, or of the night sky background. An object's surface brightness depends on ...
, a very blue color, low current star formation rate and low
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 ...
are consistent with it being a small (background)
dwarf irregular galaxy, perhaps similar to
Local Group
The Local Group is the galaxy group that includes the Milky Way, where Earth is located. It has a total diameter of roughly , and a total mass of the order of .
It consists of two collections of galaxies in a " dumbbell" shape; the Milky Way ...
dwarfs such as
IC 1613 and
Sextans A. Arguments based on the observed radial velocity and the tentative detection of the RGB tip suggest that it lies well outside the confines of the Local Group.
Further study using the Hubble Space Telescope has shown it to be a solitary irregular dwarf galaxy. The galaxy is between 22 and 24 million light years from Earth, and so is not close to the Andromeda Galaxy at all. The galaxy is severely isolated. The Holmberg diameter is 1880 parsecs, but neutral atomic hydrogen gas extends more than eight times further out in a disk. The galaxy is very dark, and the baryonic mass to
dark matter
In astronomy, dark matter is an invisible and hypothetical form of matter that does not interact with light or other electromagnetic radiation. Dark matter is implied by gravity, gravitational effects that cannot be explained by general relat ...
ratio is 0.11.
History
It was discovered by
Sidney van den Bergh
Sidney Van den Bergh (born 20 May 1929) is a retired Dutch-Canadian astronomer.
Van den Bergh showed an interest in science from an early age, learning to read with books on astronomy. In addition to being interested in astronomy, he also like ...
in 1972.
See also
*
List of Andromeda's satellite galaxies
The Andromeda Galaxy (M31) has satellite galaxies just like the Milky Way. Orbiting M31 are at least 35 dwarf galaxies: the brightest and largest is M110, which can be seen with a basic telescope. The second-brightest and closest one to M31 is ...
References
External links
{{DEFAULTSORT:Andromeda 04
Dwarf irregular galaxies
Andromeda (constellation)
Astronomical objects discovered in 1972
Virgo Supercluster
Field galaxies
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