| NGC 864 | |
|---|---|
 | |
| Observation data (J2000epoch) | |
| Constellation | Cetus[1] |
| Right ascension | 02h 15m 27,64s[1] |
| Declination | +06° 00′ 09.4″[1] |
| Redshift | +0.005210±0.000004[1] |
| Heliocentric radial velocity | 1562 ± 1 km/s[1] |
| Distance | 22.0 ± 1.5 (72 ± 5)×106 ly)[1] |
| Apparent magnitude (V) | 10.9[1] |
| Apparent magnitude (B) | 11.4[1] |
| Characteristics | |
| Type | SAB(rs)c[1] |
| Other designations | |
| NGC 864 •UGC 1736 •PGC 8631 •CGCG 413-066 •MCG +01-06-061 •IRAS 02128+0546 •KUG 0211+276 •2MASX J02152764+0600094 •CN 510 | |
NGC 864 is astar-formingintermediate spiral galaxy located in theCetus constellation.[1] It's also classified as an isolated galaxy on the AMIGA (Analysis of the Interstellar Medium of Isolated Galaxies) catalogue as CIG 96.[2] Its discovery and first description was realized byWilliam Herschel in October 25th, 1785[3] and the findings made public through hisCatalogue of Nebulae and Clusters of Stars, published in 1786.
Due to its diameter, declination and inclination, NGC 864 was selected in 2012 by a group of astronomers working at theRoque de los Muchachos Observatory as an object forkinematics study. Besides collecting data to help understand NGC 864's morphology, the objective of the project was to develop a method offlux-calibration for the newGHαFaS system on theWilliam Herschel Telescope.[4][5]
Galaxies are the basic building blocks of the Universe and their formation is of great interest in current astrophysical research. A galaxy's morphology is the result of both externally driven (like agalaxy merger) and internal evolution (as in a spiral pattern driven).[4] UsingACAM and GHαFaS to producehigh spectral resolutionHα images of NGC 864, andintegral-field spectrograph data, astronomers were able to determine itsbar presents bright regions of massive star formation at the ends, where twoasymmetric arms arise.[5]
NGC 864's outer spiral shows a flocculent pattern, leading some astronomers to classify it as agrand design galaxy.[5]
Due to its isolation, one of the most interesting characteristics of this galaxy is its asymmetry. The asymmetry in galaxies located in high-density areas is often the result of galaxy-galaxy interaction, like in a merger. The origin of asymmetries in isolated galaxies however, is not well understood. Some astronomers suggest it could originate from long-lived dynamical instabilities.[6]
In a study from 2005, astronomers realized an integralHIspectra of NGC 864, producing a detailed analysis of its HI density distribution and velocity field. The data showed theinterstellar medium to be symmetric in velocity, but asymmetric in intensity, suggesting the possibility of its asymmetry being the result of an internal dynamical instability unlikely. The researchers speculate NGC 864's asymmetry might have been the result of a minor galaxy companion crossing the equatorial plane just outside the optical disc but still within the extendedHI disc, causing the warp we can observe today.[6]
