Pisces II (dwarf galaxy)

Pisces II Dwarf Galaxy
Observation data (J2000 epoch)
Constellation	Pisces
Right ascension	22^h 58^m 31^s[1]
Declination	+05° 57′ 09″[1]
Distance	585 kly (180 kpc)[1]
Apparent magnitude (V)	16.3[1]
Characteristics
Type	dSph
Apparent size (V)	2.2+0.2 −0.2′[1]
Other designations
Pisces II

Pisces II is a dwarf spheroidal galaxy situated in the Pisces constellation and discovered in 2010 in the data obtained by the Sloan Digital Sky Survey.^[1] The galaxy is located at the distance of about 180 kpc (kiloparsecs) from the Sun. It is classified as a dwarf spheroidal galaxy (dSph) meaning that it has an elongated shape with the half-light radius of about 60 pc and ratio of the axis of about 5:3.^[1]

Pisces II is one of the smallest and faintest satellites of the Milky Way—its integrated 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. The stellar population of Pisces II consists mainly of moderately old stars formed 10–12 billion years ago. The metallicity of these old stars is low at −2.3 < [Fe/H] < −1.7, which means that the percentage of their mass that consists of "heavy metals"^{[upper-alpha 1]} is no more than 1/80 of the corresponding percentage in the Sun.^[1]

In 2016, follow-up work on Pegasus III highlighted that both it and Pisces II lie relatively close to each other (within approximately 43 kpc) and share similar radial velocities in the Galactic standard of rest frame (note: this is not the same as the LSR). This suggests that these two satellite galaxies may actually be associated with one another, although further spectroscopic measurements are required to confirm this.^[2]

Notes

1. In astronomy and physical cosmology, unlike other physical sciences, "heavy metals" refers to all elements except hydrogen and helium.

References

1. Belokurov, V.; Walker, M. G.; Evans, N. W.; Gilmore, G.; Irwin, M. J.; Just, D.; Koposov, S.; Mateo, M.; Olszewski, E.; Watkins, L.; Wyrzykowski, L. (2010). "Big Fish, Little Fish: Two New Ultra-Faint Satellites of the Milky Way". The Astrophysical Journal. 712: L103. arXiv:1002.0504. Bibcode:2010ApJ...712L.103B. doi:10.1088/2041-8205/712/1/L103.
2. Kim, Dongwon; Jerjen, Helmut; Geha, Marla; Chiti, Anirudh; Milone, Antonino P.; Mackey, Dougal; da Costa, Gary; Frebel, Anna; Conn, Blair. "PORTRAIT OF A DARK HORSE: PHOTOMETRIC PROPERTIES AND KINEMATICS OF THE ULTRA-FAINT MILKY WAY SATELLITE PEGASUS III". arXiv:1608.04934 [astro-ph.GA].