Leo IV (dwarf galaxy)
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| Leo IV Dwarf Galaxy[1] | |
|---|---|
| Observation data (J2000 epoch) | |
| Constellation | Leo |
| Right ascension | 11h 32m 57s[1] |
| Declination | −00° 32′ 00″[1] |
| Distance | 520+49−45 kly (160+15−14 kpc)[2] 154 ± 4 kpc[3] |
| Type | dSph[2] |
| Apparent dimensions (V) | 6.8′[2] |
| Apparent magnitude (V) | 15.9 ± 0.5[2] |
| Other designations | |
| Leo IV[1] | |
| See also: Galaxy, List of galaxies | |
Leo IV is a dwarf spheroidal galaxy situated in the Leo constellation and discovered in 2006 in the data obtained by Sloan Digital Sky Survey.[2] The galaxy is located at the distance of about 160 kpc from the Sun and moves away from the Sun with the velocity of about 130 km/s.[2][4] It is classified as a dwarf spheroidal galaxy (dSph) meaning that it has an approximately round shape with the half-light radius of about 160 pc.[2][note 1]
Leo IV is one of the smallest and faintest satellites of the Milky Way-its integrated luminosity is about 16,000 times that of the Sun (absolute visible magnitude of about −5.7), which is much lower than the luminosity of a typical globular cluster.[3] However, its mass is about 1.5 million solar masses, which means that Leo's mass to light ratio is around 150. A high mass to light ratio implies that Leo IV is dominated by the dark matter.[4]
The stellar population of Leo IV consists mainly of old stars formed more than 12 billion years ago.[3] The metallicity of these old stars is also very low at [Fe/H] ≈ −2.58 ± 0.75, which means that they contain 400 times less heavy elements than the Sun.[5] The observed stars were primarily red giants, although a number of Horizontal branch stars including three variable RR Lyrae stars were also discovered.[3][note 2] The stars of Leo IV were probably among the first stars to form in the Universe. Nevertheless, the detailed study of the stellar population revealed the presence of a small number of much younger stars with the age of about 2 billion years or less. This discovery points to a complicated star formation history of this galaxy.[3] Currently there is no star formation in Leo IV. The measurements have so far failed to detect any neutral hydrogen in it-the upper limit is just 600 solar masses.[6]
In 2008, another galaxy called Leo V was discovered in the vicinity of Leo IV. The former is located 20 kpc further from the Milky Way than the latter and 3 degrees (~ 10 kpc) away from it. These two galaxies may be physically associated with each other.[7]
Notes
References
- ^ a b c d "SIMBAD Astronomical Database". Results for Leo IV Dwarf Galaxy. http://simbad.u-strasbg.fr/Simbad. Retrieved 2010-01-31.
- ^ a b c d e f g Belokurov, V.; Zucker, D. B.; Evans, N. W. et al. (2007). "Cats and Dogs, Hair and a Hero: A Quintet of New Milky Way Companions". The Astrophysical Journal 654: 897-906. doi:10.1086/509718. arXiv:astro-ph/0608448. http://adsabs.harvard.edu/abs/2007ApJ...654..897B.
- ^ a b c d e f g Sand, David J.; Seth, Anil; Olszewski, Edward W. et al. (2010). "A Deeper Look at Leo IV: Star Formation History and Extended Structure". The Astrophysical Journal (submitted). arXiv:0911.5352. http://adsabs.harvard.edu/abs/2009arXiv0911.5352S.
- ^ a b Simon, Joshua D.; Geha, Marla (2007). "The Kinematics of the Ultra-faint Milky Way Satellites: Solving the Missing Satellite Problem". The Astrophysical Journal 670: 313-331. doi:10.1086/521816. arXiv:0706.0516. http://adsabs.harvard.edu/abs/2007ApJ...670..313S.
- ^ Kirby, Evan N.; Simon, Joshua D.; Geha, Marla et al. (2008). "Uncovering Extremely Metal-Poor Stars in the Milky Way's Ultrafaint Dwarf Spheroidal Satellite Galaxies". The Astrophysical Journal 685: L43-L46. doi:10.1086/592432. arXiv:0807.1925. http://adsabs.harvard.edu/abs/2008ApJ...685L..43K.
- ^ Grcevich, Jana; Putman, Mary E. (2009). "H I in Local Group Dwarf Galaxies and Stripping by the Galactic Halo". The Astrophysical Journal 696: 385-395. doi:10.1088/0004-637X/696/1/385. arXiv:0901.4975. http://adsabs.harvard.edu/abs/2009ApJ...696..385G.
- ^ Belokurov, V.; Walker, M. G.; Evans, N. W. et al. (2008). "Leo V: A companion of a companion of the Milky Way galaxy". The Astrophysical Journal 686: L83-L86. doi:10.1086/592962. arXiv:0807.2831. http://adsabs.harvard.edu/abs/2008ApJ...686L..83B.
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