| 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) | 5.7′[3] |
| 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 130 pc.[3][note 1]
Leo IV is one of the smallest and faintest satellites of the Milky Way—its integrated luminosity is about 15,000 times that of the Sun (absolute visible magnitude of −5.5 ± 0.3), 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]
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