NGC 4622 is a face-on

unbarred spiral galaxy An unbarred spiral galaxyAstronomy Pictures(accessed 18 April 2010) 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. Ba ...

with a very prominent ring structure located 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 origins of the e ...

Centaurus Centaurus is a bright constellation in the southern sky. One of the 88 modern constellations by area, largest constellations, Centaurus was included among the 48 constellations listed by the 2nd-century astronomer Ptolemy, and it remains one o ...

. The galaxy is a member of the Centaurus Cluster.

Spiral structure

The spiral galaxy, NGC 4622 (also called Backward galaxy), lies approximately 111 million light years away from Earth in the constellation Centaurus. NGC 4622 is an example of a galaxy with leading

spiral arm Spiral galaxies form a class of galaxy originally described by Edwin Hubble in his 1936 work ''The Realm of the Nebulae'' Each spiral arm winds away from the center of the galaxy and ends at an outermost tip that "points" in a certain direction (away from the arm). Spiral arms were thought to always trail, meaning that the outermost tip of every spiral arm points away from the direction of the disk's orbital rotation. This is true of the ''inner'' spiral arm of NGC 4622 but not of its ''outer'' spiral arms. The outer arms of NGC 4622 are instead leading spiral arms, meaning the tips of the spiral arms point towards the direction of disk rotation. This may be the result of a gravitational interaction between NGC 4622 and another galaxy or the result of a merger between NGC 4622 and a smaller object. NGC 4622 also has a single inner trailing spiral arm. Although it was originally suspected that the inner spiral arm was a leading arm, the observations that established that the outer arms were leading also established that the inner arm was trailing. These results were met with skepticism in part because they contradicted conventional wisdom with one quote being “so you’re the backward astronomers who found the backward galaxy.” The fact that a pair of arms could lead was not easy to accept. Astronomical objections centered on the fact that dust reddening and cloud silhouettes were used to determine that the outer arms lead. The galaxy disk is tilted only 19 degrees from face-on making near to far-side effects of dust hard to discern and because clumpy dust clouds might be concentrated on one side of the disk, creating misleading results. In response, the “backward astronomers” determined NGC 4622's spiral arm sense with a method independent of the previous work. The new Fourier component method is actually assisted by the small tilt, and dust reddening and cloud silhouettes are not used in the latest analysis. The Fourier component method reveals two new weak arms in the inner disk winding opposite the outer strong clockwise pair. Thus the galaxy ''must'' have a pair of arms winding in the opposite direction from most galaxies. Analysis of a color-age star formation angle sequence of the Fourier components establishes that the strong outer pair is the leading pair. While the presence of backward arms in a galaxy may seem like an inconvenient truth to many, two independent methods now indicate that NGC 4622's arms do indeed behave in a very unusual fashion, with the outer arms winding outward in the same direction the disk turns. A Fourier component image of the arm pairs is shown with one of the pair of arms marked for the newly discovered inner CCW pair (black dots) as well as one of the already known (CW) outer pair (white dots).

Supernova

On May 25, 2001, an image taken by the

Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most versa ...

captured a supernova in NGC 4622. It was discovered by R. Buta and GG Byrd of the University of Alabama as well as T. Freeman of

Bevill State Community College Bevill State Community College is a public community college in Sumiton, Alabama. It enrolls 3,986 students and has been accredited by the Commission on Colleges of the Southern Association of Colleges and Schools since 1994. , the college had ...

. The type of supernova was not determined.

Group and cluster

According to AM Garcia, NGC 4622 is a member of the

NGC 4709 NGC 4709 is an elliptical galaxy located in the constellation Centaurus. It is considered to be a member of the Centaurus Cluster and is the dominant member of a small group of galaxies known as "Cen 45" which is currently merging with the main ...

group which consists of at least 42 galaxies including

NGC 4616 NGC commonly refers to: * New General Catalogue of Nebulae and Clusters of Stars, a catalogue of deep sky objects in astronomy NGC may also refer to: Companies * NGC Corporation, name of US electric company Dynegy, Inc. from 1995 to 1998 * Nat ...

NGC 4622B NGC commonly refers to: * New General Catalogue of Nebulae and Clusters of Stars, a catalogue of deep sky objects in astronomy NGC may also refer to: Companies * NGC Corporation, name of US electric company Dynegy, Inc. from 1995 to 1998 * Nat ...

(also called

PGC 42852 PGC may refer to: *Pennsylvania Game Commission *Persian Gulf Cup, Iran's highest association football league *PGC (gene) *PGC 1000714, a ring galaxy * PGC-1α, a protein which is the master regulator of mitochondrial biogenesis *Playwrights Guild o ...

NGC 4679 NGC commonly refers to: * New General Catalogue of Nebulae and Clusters of Stars, a catalogue of deep sky objects in astronomy NGC may also refer to: Companies * NGC Corporation, name of US electric company Dynegy, Inc. from 1995 to 1998 * Nat ...

and

. The NGC 4709 group is part of the Centaurus Cluster.

References

External links

*
Hubble Heritage site: Pictures and description

SKY-MAP.ORG : NGC 4622
{{DEFAULTSORT:NGC 4622 Ring galaxies Unbarred spiral galaxies 4622 42701 Centaurus (constellation) Centaurus Cluster

Spiral structure

Supernova

Group and cluster

See also

References

External links