| Leo A | |
| Type: | IBm[1] |
| Dist Ly: | 2.6 ± 0.1 Mly (790 ± 40 kpc)[2] [3] |
| Z: | 0.000067 |
| Appmag V: | 12.9 |
| Size V: | 5.1 × 3.1 |
| Constellation Name: | Leo |
| Names: | Leo III, UGC 5364, DDO 69, PGC 28868 |
Leo A (also known as Leo III) is an irregular galaxy that is part of the Local Group. It lies 2.6 million light-years from Earth, and was discovered by Fritz Zwicky in 1942.[4] The estimated mass of this galaxy is solar masses, with at least 80% consisting of dark matter.[5] It is one of the most isolated galaxies in the Local Group and shows no indications of an interaction or merger for several billion years. However, Leo A is nearly unique among irregular galaxies in that more than 90% of its stars formed more recently than 8 billion years ago, suggesting a rather unusual evolutionary history.[6] The presence of RR Lyrae variables shows that the galaxy has an old stellar population that is up to 10 billion years in age.[7]
The neutral hydrogen in this galaxy occupies in a volume similar to its optical extent, and is distributed in a squashed, uneven ring. The galaxy is not rotating and the hydrogen is moving about in random clumps. The proportion of elements with higher atomic numbers than helium is only about 1-2% of the ratio in the Sun. This indicates a much less complete conversion of gas into stars than in the Milky Way galaxy. The Leo A galaxy shows sign of increased star formation some time within the last 1-4 billion years, although the current level is low. There are four H II regions powered by short-lived, O-class stars.[8]