Pisces II
Galaxy in the constellation Pisces
From Wikipedia, the free encyclopedia
Pisces II (Psc II)[6][A] is an ultra-faint dwarf-spheroidal galaxy and satellite of the Milky Way, located in the Pisces constellation 180 kpc (587,081 light years) from Earth.[1] Discovered in 2009 by public analysis of Data Release 7 (DR7) of the Sloan Digital Sky Survey,[1] it is classified as a dwarf spheroidal galaxy (dSph) and is one of the smallest and faintest satellite galaxies of the Milky Way.[2][7]
| Pisces II | |
|---|---|
| Observation data (J2000 epoch) | |
| Constellation | Pisces |
| Right ascension | 22h 58m 31s[1] |
| Declination | +05° 57′ 09″[1] |
| Distance | 585 kly (180 kpc)[1] |
| Apparent magnitude (V) | 17.03[2] |
| Absolute magnitude (V) | −4.28[2] |
| Characteristics | |
| Type | dSph |
| Apparent size (V) | 2.2+0.2 −0.2′[1] |
| Other designations | |
| Pisces II,[3] Psc II[4][A] | |
Structure
Pisces is a small irregular galaxy, with a moderately-aged and older stellar population of metal-poor stars, consisting primarily of stars formed about 10 billion years ago.[1][8] The metallicity of these old stars is low, at −2.3 < [Fe/H] < −1.7, which means that the ratio of their mass that consists of heavy metals[B] is less than that of the Sun.[1] Its luminosity is about 10,000 times that of the Sun (absolute magnitude of about −5), which corresponds to the luminosity of an average globular cluster.[6][8]
Potential past interactions
In 2016, follow-up work on Pisces II and Pegasus III[8] highlighted that both lie relatively close to each other (within approximately 43 kiloparsecs), and share similar radial velocities in the Milky Way's rest frame.[2][8] This suggests that these two satellite galaxies may actually be associated with one another, potentially having interacted in the past; however, further spectroscopic measurements are needed to confirm this.[2][7]
See also
- Satellite galaxies of the Milky Way
- Pisces VII, a dwarf satellite galaxy of the Triangulum galaxy
- Pisces A and Pisces B, two void dwarf galaxies in the Local Group
Notes
- Andromeda II was also given the alias Pisces II by Martin et al. (2009), who also proposed aliases for several other satellite galaxies of the Andromeda Galaxy[5] However, that name was later used by a different group unaware of these names, for this object.
- In astronomy and physical cosmology, unlike other physical sciences, "heavy metals" refers to all elements except hydrogen and helium.