NGC 4618

NGC 4618
An image of NGC 4618 taken with HST.
Observation data (J2000 epoch)
Constellation	Canes Venatici[1]
Right ascension	12h 41m 32.8s[2]
Declination	+41° 09′ 03″[2]
Redshift	544 ± 1 km/s[2]
Type	SB(rs)m[2]
Apparent dimensions (V)	4'.2 × 3'.4[2]
Apparent magnitude (V)	11.2[2]
Notable features	asymmetric; single spiral arm[3]
Other designations
IC 3667,[2] UGC 7853,[2] PGC 042575,[2] Arp 23,[2] VV 73[2]
See also: Galaxy, List of galaxies

NGC 4618 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.

Structure

Unlike most spiral galaxies, NGC 4618 has a single spiral arm, which gives the galaxy an asymmetric appearance.^[3] This galaxy was included in the Atlas of Peculiar Galaxies as one of three examples of nearby galaxies with single spiral arms.^[4] Although NGC 4618 is labeled as peculiar, many similar galaxies have been identified.

It has been hypothesized that this galaxy's asymmetric structure may be the result of a gravitational interaction with NGC 4625.^[3] Such asymmetric structure is commonly seen among many interacting galaxies. However, observations of neutral hydrogen gas in NGC 4618 and NGC 4625 imply that only some of the gas outside the optical disks of NGC 4618 is affected by the gravitational interaction.^[5] This may indicate that NGC 4618's one-arm shape forms as the result of processes that are intrinsic to the galaxy itself.

Environment

As mentioned above, NGC 4618 is interacting with NGC 4625.^[3]

See also

• Canes II Group
• NGC 5713 - a similar asymmetric spiral galaxy

References

1. ^ R. W. Sinnott, editor (1988). The Complete New General Catalogue and Index Catalogue of Nebulae and Star Clusters by J. L. E. Dreyer. Sky Publishing Corporation and Cambridge University Press. ISBN 0-933-34651-4. 
2. ^ ^{a b c d e f g h i j k} "NASA/IPAC Extragalactic Database". Results for NGC 4618. http://nedwww.ipac.caltech.edu/. Retrieved 2006-11-15. 
3. ^ ^{a b c d} A. Sandage, J. Bedke (1994). Carnegie Atlas of Galaxies. Washington, D.C.: Carnegie Institution of Washington. ISBN 0-87279-667-1. 
4. ^ H. Arp (1966). "Atlas of Peculiar Galaxies". Astrophysical Journal Supplement 14: 1–20. Bibcode 1966ApJS...14....1A. doi:10.1086/190147. 
5. ^ S. J. Bush, E. M. Wilcots (2004). "Neutral Hydrogen in the Interacting Magellanic Spirals NGC 4618 and NGC 4625". Astrophysical Journal 128 (6): 2789–2796. arXiv:astro-ph/0409209. Bibcode 2004AJ....128.2789B. doi:10.1086/425876. 

Coordinates: 12^h 41^m 32.8^s, +41° 09′ 03″