Magellanic spiral

Magellanic spiral galaxies are (usually) dwarf galaxies which are classified as the type Sm (and SAm, SBm, SABm). They are galaxies with one single spiral arm, and are named after their prototype, the Large Magellanic Cloud, an SBm galaxy. They can be considered to be intermediate between dwarf spiral galaxies and irregular galaxies.

Magellanic spirals

SAm galaxies are a type of unbarred spiral galaxy, while SBm are a type of barred spiral galaxy.[1] SABm are a type of intermediate spiral galaxy.

Type Sm and Im galaxies have also been categorized as irregular galaxies with some structure (type Irr-1). Sm galaxies are typically disrupted and asymmetric.[2] dSm galaxies are dwarf spiral galaxies or dwarf irregular galaxies, depending on categorization scheme.

The Magellanic spiral classification was introduced by Gerard de Vaucouleurs, along with Magellanic irregular (Im), when he revamped the Hubble classification of galaxies.

Grades

Magellanic Spiral Galaxies
Magellanic Spirals
Example Type Image Information Notes
SAdm
SAm
SABdm
SABm
SBdm
Large Magellanic Cloud SBm Large.mc.arp.750pix A satellite of the Milky Way, and the prototype galaxy for the Magellanic Spiral class
Sdm
Sm
Dwarf Magellanic Spirals
Example Type Image Information Notes
dSAdm
dSAm
dSABdm
dSABm
dSBdm
dSBm
dSdm
dSm

List of Magellanic spirals

Barred (SBm)

Intermediate (SABm)

Unbarred (SAm)

See also

References

  1. ^ Linda S. Sparke, John Sill Gallagher, "Galaxies in the Universe: An Introduction", 2ed., Cambridge University Press, '2007', ISBN 978-0-521-85593-8
  2. ^ citeBase; Neutral Hydrogen in the Interacting Magellanic Spirals NGC 4618/4625 Archived 14 February 2012 at the Wayback Machine; Stephanie J. Bush; Eric M. Wilcots; (accessed 1 March 2009)
  3. ^ Paul B. Eskridge; "Recent Star and Cluster Formation in the Nearby Magellanic Spiral NGC 1311"; 'American Astronomical Society Meeting' 208, #14.04; Bulletin of the American Astronomical Society, Vol. 38, p.93; (accessed 1 March 2009)
  4. ^ University of Wisconsin, BARRED MAGELLANIC SPIRALS (accessed 1 March 2009)
  5. ^ NASA/IPAC Extragalactic Database
Barred spiral galaxy

A barred spiral galaxy is a spiral galaxy with a central bar-shaped structure composed of stars. Bars are found in between one third and two thirds of all spiral galaxies. Bars generally affect both the motions of stars and interstellar gas within spiral galaxies and can affect spiral arms as well. The Milky Way Galaxy, where our own Solar System is located, is classified as a barred spiral galaxy.Edwin Hubble classified spiral galaxies of this type as "SB" (spiral, barred) in his Hubble sequence and arranged them into sub-categories based on how open the arms of the spiral are. SBa types feature tightly bound arms, while SBc types are at the other extreme and have loosely bound arms. SBb-type galaxies lie in between the two. SB0 is a barred lenticular galaxy. A new type, SBm, was subsequently created to describe somewhat irregular barred spirals, such as the Magellanic Clouds, which were once classified as irregular galaxies, but have since been found to contain barred spiral structures. Among other types in Hubble's classifications for the galaxies are the spiral galaxy, elliptical galaxy and irregular galaxy.

David Dunlap Observatory Catalogue

David Dunlap Observatory Catalogue, known as the DDO or A Catalogue of Dwarf Galaxies, is a catalogue of dwarf galaxies that was published in 1959 (and later expanded in 1966) by Sidney van den Bergh.

Density wave theory

Density wave theory or the Lin-Shu density wave theory is a theory proposed by C.C. Lin and Frank Shu in the mid-1960s to explain the spiral arm structure of spiral galaxies. The Lin-Shu theory introduces the idea of long-lived quasistatic spiral structure(QSSS hypothesis). In this hypothesis, the spiral pattern rotates in a particular angular frequency (pattern speed), whereas the stars in the galactic disk are orbiting at a different speed depending their distance to the galaxy center. The presence of spiral density waves in galaxies has implications on the star formation, since the gas orbiting around the galaxy may be compressed and form shock periodically. Theoretically, the formation of global spiral pattern is treated as an instability of the stellar disk caused by the self-gravity, as opposed to tidal interactions. The mathematical formulation of the theory has also been extended to other astrophysical disk systems, such as Saturn's rings.

Intermediate spiral galaxy

An intermediate spiral galaxy is a galaxy that is in between the classifications of a barred spiral galaxy and an unbarred spiral galaxy. It is designated as SAB in the galaxy morphological classification system devised by Gerard de Vaucouleurs. Subtypes are labeled as SAB0, SABa, SABb, or SABc, following a sequence analogous to the Hubble sequence for barred and unbarred spirals. The subtype (0, a, b, or c) is based on the relative prominence of the central bulge and how tightly wound the spiral arms are.

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 appearance, with neither a nuclear bulge nor any trace of spiral arm structure.Collectively they are thought to make up about a quarter of all galaxies. Some irregular galaxies were once spiral or elliptical galaxies but were deformed by an uneven external gravitational force. Irregular galaxies may contain abundant amounts of gas and dust. This is not necessarily true for dwarf irregulars.Irregular galaxies are commonly small, about one tenth the mass of the Milky Way galaxy. Due to their small sizes, they are prone to environmental effects like crashing with large galaxies and intergalactic clouds.

Large Magellanic Cloud

The Large Magellanic Cloud (LMC) is a satellite galaxy of the Milky Way. At a distance of about 50 kiloparsecs (≈163,000 light-years), the LMC is the second- or third-closest galaxy to the Milky Way, after the Sagittarius Dwarf Spheroidal (~16 kpc) and the possible dwarf irregular galaxy known as the Canis Major Overdensity. Based on readily visible stars and a mass of approximately 10 billion solar masses, the diameter of the LMC is about 14,000 light-years (4.3 kpc), making it roughly one one-hundredth as massive as the Milky Way. This makes the LMC the fourth-largest galaxy in the Local Group, after the Andromeda Galaxy (M31), the Milky Way, and the Triangulum Galaxy (M33).

The LMC is classified as a Magellanic spiral. It contains a stellar bar that is geometrically off-center, suggesting that it was a barred dwarf spiral galaxy before its spiral arms were disrupted, likely by tidal interactions from the Small Magellanic Cloud (SMC), and the Milky Way's gravity.With a declination of about -70°, the LMC is visible as a faint "cloud" only in the southern celestial hemisphere and from latitudes south of 20° N, straddling the border between the constellations of Dorado and Mensa, and appears longer than 20 times the Moon's diameter (about 10° across) from dark sites away from light pollution.The Milky Way and the LMC are expected to collide in approximately 2.4 billion years.

Magellanic

Magellanic may refer to:

Magellanic Steppe, 7th largest desert in the world, see Patagonian Desert

Magellanic Straits, a sea passageway at the tip of South America, see Strait of Magellan

Magellanic subpolar forests, an ecoregion of southernmost Chile and Argentina

Magellanic Premium, a major prize established in 1786 regarding navigation

Magellanic Clouds

The Magellanic Clouds (or Nubeculae Magellani) are two irregular dwarf galaxies visible in the Southern Celestial Hemisphere; they are members of the Local Group and are orbiting the Milky Way galaxy. Because both show signs of a bar structure, they are often reclassified as Magellanic spiral galaxies.

The two galaxies are:

Large Magellanic Cloud (LMC), approximately 160,000 light-years away

Small Magellanic Cloud (SMC), approximately 200,000 light years away

NGC 2552

NGC 2552 is a Magellanic spiral galaxy located some 22 million light years away in the faint northern constellation of Lynx. This is a type of unbarred dwarf galaxy, usually with a single spiral arm. It is inclined by 41° to the line of sight from the Earth along a position angle of 229°. The measured velocity dispersion of the stars in NGC 2552 is relatively low—a mere 19 ± 2 km/s. This galaxy forms part of a loose triplet that includes NGC 2541 and NGC 2500, which together belong to the NGC 2841 group.

NGC 4523

NGC 4523 is a Magellanic spiral galaxy located about 35 to 50 million light-years away in the constellation Coma Berenices. It was discovered by astronomer Heinrich d'Arrest on April 19, 1865. NGC 4523 is member of the Virgo Cluster.

NGC 4618

NGC 4618 is a distorted barred dwarf galaxy in the constellation Canes Venatici. The galaxy is formally classified as a Sm galaxy, which means that its structure vaguely resembles the structure of spiral galaxies. The galaxy is sometimes referred to as a Magellanic spiral because of its resemblance to the Magellanic clouds.

NGC 4625

NGC 4625 is a distorted dwarf galaxy in the constellation Canes Venatici. The galaxy is formally classified as a Sm galaxy, which means that its structure vaguely resembles the structure of spiral galaxies. The galaxy is sometimes referred to as a Magellanic spiral because of its resemblance to the Magellanic clouds.

NGC 5002

NGC 5002 is a Magellanic spiral galaxy in Canes Venatici. It was discovered by Heinrich d'Arrest in 1865. It is also known as MCG 6-29-51, PGC 45728, UGC 8254.It has an apparent size of 1.7 by 1.0 arcmin.

NGC 5204

NCG 5204 is a Magellanic spiral galaxy located about 14.5 million light-years away from Earth in the constellation of Ursa Major and is a member of the M101 Group of galaxies. It has a galaxy morphological classification of SA(s)m and is highly irregular, with only the barest indication of any spiral arm structure. The galaxy's most prominent feature is an extremely powerful X-ray source designated NGC 5204 X-1. This has resulted in the galaxy being the target of several studies due to the strength of the source and its relative proximity to Earth.

NGC 925

NGC 925 is a barred spiral galaxy located about 30 million light-years away in the constellation Triangulum. The morphological classification of this galaxy is SB(s)d, indicating that it has a bar structure and loosely wound spiral arms with no ring. The spiral arm to the south is stronger than the northern arm, with the latter appearing flocculent and less coherent. The bar is offset from the center of the galaxy and is the site of star formation all along its length. Both of these morphological traits—a dominant spiral arm and the offset bar—are typically characteristics of a Magellanic spiral galaxy. The galaxy is inclined at an angle of 55° to the line of sight along a position angle of 102°.The galaxy is a member of the NGC 1023 Group, a nearby, gravitationally-bound group of galaxies associated with NGC 1023. However, the nearest member lies at least 650,000 ly (200,000 pc) distant from NGC 925. There is a 10 million solar mass (M☉) cloud of neutral hydrogen attached to NGC 925 by a streamer. It is uncertain whether this is a satellite dwarf galaxy, the remnant of a past tidal interaction, or a cloud of primordial gas.

UGCA 86

UGCA 86 is a magellanic spiral galaxy. It was first thought to be part of the Local Group, but after the brightest stars in the galaxy were observed, it became clear that it was located in the IC 342/Maffei Group. UGCA 86 is thought to be a satellite galaxy of IC 342, however the separation between the two galaxies is over 50% larger than the distance between the Milky Way and the Magellanic Clouds.

Unbarred spiral galaxy

An unbarred spiral galaxy is a type of spiral galaxy without a central bar, or one that is not a barred spiral galaxy. It is designated with an SA in the galaxy morphological classification scheme.

The Sombrero Galaxy is an unbarred spiral galaxy.

Barless spiral galaxies are one of three general types of spiral galaxies under the de Vaucouleurs system classification system, the other two being intermediate spiral galaxy and barred spiral galaxy. Under the Hubble tuning fork, it is one of two general types of spiral galaxy, the other being barred spirals.

Morphology
Structure
Active nuclei
Energetic galaxies
Low activity
Interaction
Lists
See also

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