Segue 2
| Segue 2 Dwarf Galaxy[1] | |
|---|---|
| Observation data (J2000 epoch) | |
| Constellation | Aries |
| Right ascension | 02h 19m 16s[1] |
| Declination | 20° 10′ 31″[1] |
| Distance | 114 kly (35 kpc)[2] |
| Apparent magnitude (V) | 15.2 ± 0.2[2] |
| Characteristics | |
| Type | dSph[2] |
| Mass | 5.5×105[2] M☉ |
| Mass/Light ratio | 650[2] M☉/L☉ |
| Apparent size (V) | 6.8+0.4 −0.4′[2] |
| Other designations | |
| Segue 2[2] | |
Segue 2 is a dwarf spheroidal galaxy situated in the constellation Aries and discovered in 2007 in the data obtained by Sloan Digital Sky Survey.[2] The galaxy is located at the distance of about 35 kpc (35,000 parsecs (110,000 ly)) from the Sun and moves towards the Sun with the speed of 40 km/s.[2] It is classified as a dwarf spheroidal galaxy (dSph) meaning that it has an approximately round shape with the half-light radius of about 34 pc.[2]
Segue 2 is one of the smallest and faintest satellites[note 1] of the Milky Way—its integrated luminosity is about 800 times that of the Sun (absolute visible magnitude of about −2.5), which is much lower than the luminosity of the majority of globular clusters.[2] However, the mass of the galaxy—about 550,000 solar masses—is substantial, corresponding to the mass to light ratio of about 650.[2]
The stellar population of Segue 2 consists mainly of old stars formed more than 12 billion years ago.[2] The metallicity of these old stars is also very low at [Fe/H] < −2, which means that they contain at least 100 times less heavy elements than the Sun.[2] The stars of Segue 2 were probably among the first stars to form in the Universe. Currently, there is no star formation in Segue 2.[2]
Segue 2 is located near the edge of Sagittarius Stream and at the same distance. It may once have been a satellite of Sagittarius Dwarf Elliptical Galaxy or its star cluster.[2]
In June 2013 the The Astrophysical Journal reported that Segue 2 was bound together with dark matter.[4][5][6]
Notes
References
- ^ a b c "SIMBAD Astronomical Database". Results for Segue 2. Retrieved 2010-02-13.
- ^ a b c d e f g h i j k l m n o p Belokurov, V.; Walker, M.G.; Evans, N.W.; et al. (2009). "Segue 2: A Prototype of the Population of Satellites of Satellites". Mon. Not. R. Astron. Soc. 397 (4): 1748–1755. arXiv:0903.0818. Bibcode:2009MNRAS.397.1748B. doi:10.1111/j.1365-2966.2009.15106.x.
{{cite journal}}: Explicit use of et al. in:|author3=(help) - ^ Martin, Nicolas F.; de Jong, Jelte T. A.; Rix, Hans-Walter (2008). "A Comprehensive Maximum Likelihood Analysis of the Structural Properties of Faint Milky Way Satellites". The Astrophysical Journal. 684 (2): 1075–1092. arXiv:0805.2945. Bibcode:2008ApJ...684.1075M. doi:10.1086/590336.
- ^ Kirby, Evan; Michael Boylan-Kolchin; Judith G. Cohen; Marla Geha; James S. Bullock; Manoj Kaplinghat (June 10, 2013). "Segue 2: The Least Massive Galaxy" (PDF). The Astrophysical Journal. doi:10.1088/0004-637X/770/1/16.
{{cite news}}: Cite has empty unknown parameters:|deadurl=and|trans_title=(help) - ^
Megan Gannon (2013-06-10). "Dwarf Galaxy Segue 2 Called Smallest Ever Discovered". Huffingtaon Post. Retrieved 2013-06-23.
The dwarf galaxy known as Segue 2 is bound together by a tiny clump of dark matter. Scientists who measured it using Hawaii's Keck Observatory say the finding adds support to theories about the formation of the universe.
{{cite news}}: Unknown parameter|deadurl=ignored (|url-status=suggested) (help) - ^ UCI Scientists Size Up Universe’s Most Lightweight Dwarf Galaxy with Keck Observatory Steve Jefferson, W. M. Keck Observatory updated June 7, 2013
| Location | Milky Way → Milky Way subgroup → Local Group → Local Sheet → Virgo Supercluster → Laniakea Supercluster → Local Hole → Observable universe → Universe Each arrow (→) may be read as "within" or "part of". |  | |||||
|---|---|---|---|---|---|---|---|
| Structure |
| ||||||
| Satellite galaxies | |||||||
| Related | |||||||
