| IC 10 | |
|---|---|
 Irregular Galaxy IC 10 | |
| Observation data (J2000epoch) | |
| Constellation | Cassiopeia |
| Right ascension | 00h 20m 17.3s[1] |
| Declination | +59° 18′ 14″[1] |
| Redshift | 0.001161±0.000003[1] |
| Distance | 2.5 ± 0.5Mly (750 ± 150kpc)[2] |
| Apparent magnitude (V) | 10.4 ± 0.2[3] |
| Characteristics | |
| Type | dIrr IV/BCD[1] |
| Size | 5000light years (diameter)[4] |
| Apparent size (V) | 6.8′ × 5.9′[1] |
| Notable features | mildstarburst galaxy |
| Other designations | |
| UGC 192,[1]PGC 1305[1] | |
IC 10 is anirregular galaxy in theconstellationCassiopeia. It was discovered byLewis Swift in 1887[5] and in 1935Nicholas Mayall became the first to suggest that the object is extragalactic.Edwin Hubble suspected it might belong to theLocal Group ofgalaxies, but its status remained uncertain for decades. Theradial velocity of IC 10 was measured in 1962, and it was found to be approaching theMilky Way at approximately 350 km/s, strengthening the evidence for its membership in the Local Group.[5] Its membership in the group was finally confirmed in 1996 by direct measurements of itsdistance based on observations ofCepheids; most estimates place the galaxy 2–3 millionlight years from Earth, with some estimates ranging from 1.5–4.5 millionlight years.[6] Despite its closeness, the galaxy is rather difficult to study because it lies near the plane of theMilky Way and is therefore heavily obscured byinterstellar matter.[7]
The apparent distance between IC 10 and theAndromeda Galaxy is about the same as the apparent distance between the Andromeda Galaxy and theTriangulum Galaxy, which suggests that IC 10 may belong to the M31 subgroup.[7]
IC 10 is the only knownstarburst galaxy in the Local Group of galaxies; it has many moreWolf–Rayet stars per squarekiloparsec (5.1 stars/kpc2) than theLarge Magellanic Cloud (2.0 stars/kpc2) or theSmall Magellanic Cloud (0.9 stars/kpc2). Although the galaxy has a luminosity similar to the SMC, it is considerably smaller, with an estimated diameter of around 5000light years.[8] Its highermetallicity compared to the SMC suggests that star formation activity has continued for a longer time period. TheH II regions in IC 10 have all formed recently, within the last 10 Myr.[9] Theevolutionary status of the Wolf–Rayet stars suggests that they all formed in a relatively short timespan. The ratio between the two types ofWolf–Rayet stars (WC stars and WN stars) in IC 10 is very different from the ratio in other galaxies in the Local Group, which may be somehow due to the starburst nature of the galaxy. Currently, the galaxy produces stars at the rate of 0.04–0.08solar masses per year, which means that the gas supply in the galaxy can last for only a few billion years longer.[7]
Observations of IC 10 in thefar-infrared show that thedust in this mild starburst galaxy is deficient in small grains.[10] It is hypothesized that any small grains that formerly existed were destroyed by strongultraviolet radiation in the areas around the hot luminous stars that were formed in the galaxy's recent burst of star formation.[11]
The galaxy has a huge envelope ofhydrogen gas, with an apparent size measuring 68′ × 80′, which is far larger than the apparent size of the galaxy in visible light (5.5′ × 7.0′). IC 10 is also unusual in the respect that the visible part of the galaxy seems to rotate in a different direction than the outer envelope.[7] It has anH II nucleus.[12]
![IC 10 taken by Hubble[13]](/mt/?noimg=&dark=on&url=https%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aSpiral%2c_elliptical%2c_irregular_IC_10.jpg)
