DDO 44 (or UGCA 133) is 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 to systems that are com ...

in the

M81 Group The M81 Group is a galaxy group in the constellations Ursa Major and Camelopardalis that includes the galaxies Messier 81 and Messier 82, as well as several other galaxies with high apparent brightnesses. The approximate center of the group i ...

, believed to be a

satellite galaxy A satellite galaxy is a smaller companion galaxy that travels on bound orbits within the gravitational potential of a more massive and luminous host galaxy (also known as the primary galaxy). Satellite galaxies and their constituents are bound ...

of the nearby

NGC 2403 NGC 2403 (also known as Caldwell 7) is an intermediate spiral galaxy in the constellation Camelopardalis. It is an outlying member of the M81 Group, and is approximately 8 million light-years distant. It bears a similarity to M33, being about 50 ...

Structure

DDO 44 is a relatively large

dwarf galaxy A dwarf galaxy is a small galaxy composed of about 1000 up to several billion stars, as compared to the Milky Way's 200–400 billion stars. The Large Magellanic Cloud, which closely orbits the Milky Way and contains over 30 billion stars, is so ...

, and it has been observed to possess a

tidal tail A tidal tail is a thin, elongated region of stars and interstellar gas that extends into space from a galaxy. Tidal tails occur as a result of galactic tide forces between interacting galaxies. Examples of galaxies with tidal tails include the ...

extending at least 50,000

parsecs The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (au), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, an ...

from its center. It has an estimated metallicity ( e/H of -1.54 ± 0.14. Due to its proximity and relative velocity to the larger

, it is believed to be NGC 2403's

. Stellar streams has been observed to originate from DDO 44, flowing towards and away for NGC 2403, indicating tidal disruptions. Around 20 percent of the galaxy's stars are believed to be of intermediate age (between 2-8 Gya), with the most recent stellar formation being estimated at 300 Mya due to a lack of young bright blue stars. This lack of bright stars caused DDO 44 to have a relatively low level of brightness. It is located approximately 3 million parsecs away from the

Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. ...

, and 79 arcminutes towards north-northwest from NGC 2403 (or approximately 75 kpc). Mass estimates based on luminosity measurements give a galactic mass of 2×10⁷–6×10⁷ M_☉. This makes DDO 44 by far NGC 2403's most massive known satellite galaxy, with the other known satellite galaxy (MADCASH J074238+652501-dw) having a mass of just ~10⁵ M_☉. H_I observations place an upper limit for DDO 44's hydrogen gas mass at 4×10⁵ M_☉.

References

Bibliography

* * * * {{DEFAULTSORT:DDO 44 Dwarf spheroidal galaxies M81 Group UGCA objects Camelopardalis (constellation)