Leo IV (dwarf galaxy)
The Leo IV dwarf galaxy Leo IV is a short spheroidal dwarf galaxy ( dSph ) in the constellation of the Lion, and was discovered in 2006 after analysis of the data of the survey of the Sloan Digital Sky Survey. The galaxy is located at a distance of about 160 kpc from the solar system and moves away from this with a speed of approximately 130 km / s
Properties
Leo IV is one of the smallest and faintest satellites of the Milky Way. The integral luminosity is about 15,000 L ☉ with an absolute magnitude of MV = (-5.5 ± 0.3 ) like what is less than that of a typical globular cluster.
Nevertheless, the mass of the galaxy with about 1.5 million M ☉ is so high that a mass-luminosity ratio of 150 results. This implies a not atypical dominance by dark matter even for this dwarf galaxy.
The stellar population of Leo IV consists mainly of older stars, which emerged more than 12 billion years ago. Thus, they are among the first stars ever to have formed in the universe. The metallicity of these old stars is correspondingly low with a value of [ Fe / H] ≈ -2.58 ± 0.75. This means that the frequency of heavy elements 400 fails times lower than in our Sun. It mainly red giant stars have been observed, although some horizontal branch stars more inclusive of three variable RR Lyrae stars have been discovered ( by determining the distance by the RR Lyrae stars amounts to (154 ± 4 ) kpc ). Detailed studies of the stellar population show for Leo IV but also with the age of 2 billion years, less a small number of much younger stars. This suggests a complex history of star formation of this galaxy. Currently, however, is no current star formation in Leo IV detectable. None of the results also indicates the presence of neutral hydrogen, the maximum upper limit of which is at most 600 M ☉.
2008, another galaxy named Leo V was discovered in the immediate vicinity of Leo IV. She is 20 kpc further away from the Milky Way as Leo IV and 3 degrees ( ~ 10 kpc ) from her. There are confirmed evidence that the two galaxies may be connected to each other physically.