| NGC 147 | |
|---|---|
.jpg) Hubble Space Telescope image of NGC 147 | |
| Observation data (J2000epoch) | |
| Constellation | Cassiopeia |
| Right ascension | 00h 33m 12.1s[1] |
| Declination | +48° 30′ 32″[1] |
| Redshift | −193±3 km/s[1] |
| Distance | 2.53 ± 0.11Mly (780 ± 30kpc)[2][3][4][a] |
| Apparent magnitude (V) | 10.5[1] |
| Characteristics | |
| Type | dSph/dE5[1] |
| Apparent size (V) | 13.2′ × 7.8′[1] |
| Notable features | satellite galaxy ofM31 |
| Other designations | |
| PGC 2004,[1]UGC 326,[1]DDO 3,[1] LEDA 2004,Caldwell 17 | |
NGC 147 (also known asDDO3 orCaldwell 17) is adwarf spheroidal galaxy about 2.58Mly away in theconstellationCassiopeia. NGC 147 is a member of theLocal Group of galaxies and asatellite galaxy of theAndromeda Galaxy (M31). It forms a physical pair with the nearby galaxyNGC 185,[5]another remote satellite of M31. It was discovered byJohn Herschel in September 1829. Visually it is both fainter and slightly larger than NGC 185 (and therefore has a considerably lower surface brightness). This means that NGC 147 is more difficult to see than NGC 185, which is visible in smalltelescopes. In theWebb Society Deep-Sky Observer's Handbook,[6] the visual appearance of NGC 147 is described as follows:
Large, quite faint, irregularly round; it brightens in the middle to a stellar nucleus.
The membership of NGC 147 in the Local Group was confirmed byWalter Baade in 1944 when he was able to resolve the galaxy into individual stars with the 100-inch (2.5 m) telescope atMount Wilson nearLos Angeles.
A survey of the brightestasymptotic giant branch (AGB) stars in the area of radius 2′ from the center of NGC 147 shows that the last significant star-forming activity in NGC 147 occurred around 3 Gyr ago.[7]NGC 147 contains a large population of older stars which show a spread inmetallicity and age. The metallicity spread suggests that NGC 147 has had chemical enrichment. However,H I has not been observed and theinterstellar medium (ISM) mass upper limit is much lower than expected had the material which is emitted from evolving stars been kept in the galaxy. This implies depletion of the ISM.[7]
At least two techniques have been used to measure distances to NGC 147. The surface brightness fluctuations distance measurement technique estimates distances to spiral galaxies based on the graininess of the appearance of their bulges. The distance measured to NGC 147 using this technique is 2.67 ± 0.18Mly (870 ± 60kpc).[2] However, NGC 147 is close enough that thetip of the red giant branch (TRGB) method may be used to estimate its distance. The estimated distance to NGC 147 using this technique is 2.21 ± 0.09 Mly (680 ± 30 kpc).[3] Averaged together, these distance measurements give a distance estimate of2.53±0.11 Mly (780±30 kpc).[a]
| Location | Andromeda Galaxy → Andromeda subgroup →Local Group →Local Sheet →Virgo Supercluster →Laniakea Supercluster →Local Hole →Observable universe →Universe Each → may be read as "within" or "part of". | .jpg) |
|---|---|---|
| Satellite galaxies |
*It is uncertain whether these are companion galaxies of the Andromeda Galaxy | |
| Catalogued stars | ||
| Other | ||
