Dwingeloo 1 is a

barred spiral galaxy A barred spiral galaxy is a spiral galaxy with a central bar-shaped structure composed of stars. Bars are found in about two thirds of all spiral galaxies in the local universe, and generally affect both the motions of stars and interstellar gas ...

about 10 million

light-year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astr ...

s away from the Earth, in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

Cassiopeia Cassiopeia or Cassiopea may refer to: Greek mythology * Cassiopeia (mother of Andromeda), queen of Aethiopia and mother of Andromeda * Cassiopeia (wife of Phoenix), wife of Phoenix, king of Phoenicia * Cassiopeia, wife of Epaphus, king of Egy ...

. It lies in the

Zone of Avoidance The Zone of Avoidance (ZOA, ZoA), or Zone of Galactic Obscuration (ZGO), is the area of the sky that is obscured by the Milky Way. The Zone of Avoidance was originally called the Zone of Few Nebulae in an 1878 paper by English astronomer Richard ...

and is heavily obscured by the

Milky Way The Milky Way or Milky Way Galaxy is the galaxy that includes the Solar System, with the name describing the #Appearance, galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galax ...

. The size and mass of Dwingeloo 1 are comparable to those of

Triangulum Galaxy The Triangulum Galaxy is a spiral galaxy 2.73 million light-years (ly) from Earth in the constellation Triangulum. It is catalogued as Messier 33 or NGC 598. With the D25 isophotal diameter of , the Triangulum Galaxy is the third-largest me ...

. Dwingeloo 1 has two smaller

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

–

Dwingeloo 2 Dwingeloo 2 is a small irregular galaxy discovered in 1996 and located about 10 million light-years away from the Earth. Its discovery was a result of the Dwingeloo Obscured Galaxy Survey (DOGS) of the Zone of Avoidance using the Dwingeloo Radio O ...

and MB 3 – and is a member of the IC 342/Maffei Group of galaxies.

Discovery

The Dwingeloo 1 galaxy was discovered in 1994 by the Dwingeloo Obscured Galaxy Survey (DOGS) using the

Dwingeloo Radio Observatory The Dwingeloo Radio Observatory is a single-dish radio telescope near the village of Dwingeloo () in the northeastern Netherlands. Construction started in 1954, and the telescope was completed in 1956. The radio telescope has a diameter of 25 ...

, which searched for neutral hydrogen (HI) radio emissions at the wavelength of 21 cm from objects in the

. In this zone gas and dust in the disk of the

galaxy block the light from the galaxies lying behind it. The galaxy was, however, first noted as an unremarkable feature on Palomar Sky Survey plates earlier in the same year, but was not recognized as such. It was also independently discovered a few weeks later by another team of astronomers working with Effelsberg 100-m Radio Telescope. Dwingeloo 1 was eventually named after the 25m radio telescope in the

Netherlands , Terminology of the Low Countries, informally Holland, is a country in Northwestern Europe, with Caribbean Netherlands, overseas territories in the Caribbean. It is the largest of the four constituent countries of the Kingdom of the Nether ...

that was used in the DOGS survey and first detected it.

Distance and group membership

Dwingeloo 1 is a highly obscured galaxy, which makes distance determination a difficult problem. The initial estimate, made soon after the discovery and based on the

Tully–Fisher relation In astronomy, the Tully–Fisher relation (TFR) is a widely verified empirical relationship between the mass or intrinsic luminosity of a spiral galaxy and its asymptotic rotation velocity or emission line width. Since the observed brightness of ...

, was about 3 Mpc. Later, this value was slightly increased to 3.5–4 Mpc. In 1999 another estimate was published, claiming a distance of more than 5 Mpc. It was based on the infrared Tully–Fisher relation. As of 2011, the distance to Dwingeloo 1 is thought to be approximately 3 Mpc, based on its likely membership in the IC 342/Maffei group. Dwingeloo 1 has two smaller

. The first one,

, is an

irregular galaxy An irregular galaxy is a galaxy that does not have a distinct regular shape, unlike a spiral or an elliptical galaxy. Irregular galaxies do not fall into any of the regular classes of the Hubble sequence, and they are often chaotic in appearan ...

, and the second, MB 3, is likely 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 as systems that are c ...

Properties

After the discovery Dwingeloo 1 was classified as a

. It has a central bar and two distinct

spiral arm Spiral arms are a defining feature of spiral galaxies. They manifest as spiral-shaped regions of enhanced brightness within the galactic disc. Typically, spiral galaxies exhibit two or more spiral arms. The collective configuration of these arms i ...

s that begin at the ends of the bar at nearly right angles and wind counterclockwise. The length of the arms is up to 180°. The disk of the galaxy is inclined with respect to the observer, with the inclination angle being 50°. The galaxy recedes from the Milky Way at a speed of about 256 km/s. The visible radius of Dwingeloo 1 is approximately 4.2', which at the distance of 3 Mpc corresponds to about 4 kpc. The neutral hydrogen is detected as far as 6 kpc (7.5') from the center. The total mass of the galaxy is about 1/4 that of the Milky Way out to the measured distance of 6 kpc or about 31 billion Solar masses. The distribution of the neutral hydrogen in Dwingeloo 1 is typical for barred spiral galaxies—it is rather flat with a minimum in the center or along the bar. The total mass of the neutral hydrogen is estimated at 370–450 million

Solar mass The solar mass () is a frequently used unit of mass in astronomy, equal to approximately . It is approximately equal to the mass of the Sun. It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxie ...

es. Dwingeloo 1 is a molecular gas-poor galaxy. The total mass of the

molecular hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

does not exceed 10% of that of neutral hydrogen. Optical observations detected around 15

H II region An H II region is a region of interstellar atomic hydrogen that is ionized. It is typically in a molecular cloud of partially ionized gas in which star formation has recently taken place, with a size ranging from one to hundreds of light year ...

s situated mainly along the spiral arms. In its overall size and mass, the galaxy is comparable to

References

External links

* * {{Cassiopeia (constellation), state=collapsed Barred spiral galaxies IC 342/Maffei Group Cassiopeia (constellation) 100170 Astronomical objects discovered in 1994 100170

Discovery

Distance and group membership

Properties

See also

References

External links