NGC 681 (also known as the Little Sombrero Galaxy) is an intermediate spiral galaxy in the constellation of Cetus, located approximately 66.5 million light-years from Earth.[1][2][4] The name Little Sombrero Galaxy is a reference to a much larger and earlier observed sombrero-like galaxy designated M104, or the Sombrero Galaxy.
NGC 681 | |
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Observation data (J2000 epoch) | |
Constellation | Cetus |
Right ascension | 01h 49m 10.829s[1] |
Declination | −10° 25′ 35.13″[1] |
Redshift | 0.00587 ± 0.00002[1] |
Heliocentric radial velocity | 1760.4 ± 6.6 km/s[1] |
Distance | ~66.5 million ly (20.39 ± 1.45 Mpc)[1] |
Apparent magnitude (V) | 12[2] |
Characteristics | |
Type | SAB(s)ab |
Mass | 1.9×1010[3] M☉ |
Mass/Light ratio | 3.6[3] M☉/L☉ |
Size | ~29.07 kpc (diameter)[1] |
Apparent size (V) | 2.70 × 1.8 arcmin[2][4] |
Other designations | |
MCG -02-05-052, PGC 6671[5] |
NGC 681 was discovered by the German-born British astronomer William Herschel on 28 November 1785 and was later also observed by William's son, John Herschel.[2] John Louis Emil Dreyer, compiler of the first New General Catalogue of Nebulae and Clusters of Stars, described NGC 681 as being a "pretty faint, considerably large, round, small (faint) star 90 arcsec to [the] west" that becomes "gradually a little brighter [in the] middle".[2]
The Little Sombrero Galaxy shares many structural similarities with its namesake, M104, although it is smaller, less luminous, and less massive. Its thin, dusty disc is seen almost perfectly edge-on and features a small, very bright nucleus in the center of a very pronounced bulge.[6] Distinctly unlike M104, NGC 681's disc contains many H II regions, where star formation is likely to be occurring.[3][6] The galaxy has a mass of 1.9×1010 M☉, a mass-to-light ratio of 3.6 , and a spiral pattern which is asymmetrical.[3]