Leo I (dwarf galaxy)

Leo I is a dwarf spheroidal galaxy in the constellation of Leo. At a distance of about 820,000 light years, it is a member of the Local Group and is among one of the most distant satellites of the Milky Way. The galaxy was discovered in 1950 by Albert George Wilson on photographic recordings in the screening of the Palomar Observatory Sky Survey with the 48-inch Schmidt telescope at Palomar Observatory.

Leo I is only 12 arc minutes of Regulus, the brightest star in the constellation Leo, removed. That is why the dwarf galaxy is sometimes referred to as Regulus dwarf. Due to the scattered light from the star to the study of the object is more difficult and it was possible to study only in the 1990s, it also visually.

Properties

Mass

The measurement of the radial velocities of some of the brightest red giant stars in the galaxy enabled the determination of the mass of Leo I It is at least (2.0 ± 1.0 ) × 107 M ⊙. However, the results are not necessarily final, also prove nor disprove the existence of dark matter halos around the galaxy. The fact that Leo I is not rotating, however, has been shown already beyond doubt.

Hypothetically, it could be in Leo I and a stream of tidal debris in the halo of our Milky Way.

Star formation

It is typical of a dwarf galaxy that their metallicity is very low. It amounts to only 1% that of the sun. Gallart et al. demonstrated in 1999 by analysis of Hubble Space Telescope images show that Leo I before 6 billion and 2 billion years experienced a massive increase in its rate of star formation. These two stages are responsible for 70 % to 80 % of the stellar population of the galaxy. For stars older than 10 billion years, no significant evidence was found. Ago about 1 billion years, the star formation appears to be rather abruptly dropped to a negligible rate. This low activity was not until some 200 million to 500 million years ago. It hereby is the youngest of the dwarf galaxies of the Milky Way subgroup. Leo I also seems embedded in a cloud of ionized gas that has a mass of the order of the galaxy.

Globular clusters

No globular clusters have been discovered in the dwarf galaxy Leo I.