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  • 21 Aug, 2019

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Leo A
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. The estimated mass of this galaxy is (8.0 ± 2.7) × 10 solar masses, with at least 80% consisting of dark matter. 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. The presence of RR Lyrae variables shows that the galaxy has an old stellar population that is up to 10 billion years in age.

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.

References

  1. ^ "NASA/IPAC Extragalactic Database". Results for Leo A. Retrieved 2006-11-19.
  2. ^ I. D. Karachentsev; V. E. Karachentseva; W. K. Hutchmeier; D. I. Makarov (2004). "A Catalog of Neighboring Galaxies". Astronomical Journal. 12745345 (4): 2031–2068. Bibcode:2004AJ....127.2031K. doi:10.1086/382905.
  3. ^ Karachentsev, I. D.; Kashibadze, O. G. (2006). "Masses of the local group and of the M81 group estimated from distortions in the local velocity field". Astrophysics. 49 (1): 3–18. Bibcode:2006Ap.....49....3K. doi:10.1007/s10511-006-0002-6. S2CID 120973010.
  4. ^ Zwicky, F (April 1942). "On the Large Scale Distribution of Matter in the Universe" (PDF). Physical Review. 61 (7–8): 489–503. Bibcode:1942PhRv...61..489Z. doi:10.1103/PhysRev.61.489.
  5. ^ Brown, Warren R.; et al. (September 2007). "Stellar Velocity Dispersion of the Leo A Dwarf Galaxy". The Astrophysical Journal. 666 (1): 231–235. arXiv:0705.1093. Bibcode:2007ApJ...666..231B. doi:10.1086/519547. S2CID 16639879.
  6. ^ Cole, Andrew; et al. (March 2007). "Leo A: A Late-blooming Survivor of the Epoch of Reionization in the Local Group". The Astrophysical Journal Letters. 659 (1): L17-20. arXiv:astro-ph/0702646. Bibcode:2007ApJ...659L..17C. doi:10.1086/516711. S2CID 14268757.
  7. ^ Vansevičius, Vladas; et al. (August 2008). "The Full-fledged Dwarf Irregular Galaxy Leo A". The Astrophysical Journal. 611 (2): L93–L96. arXiv:astro-ph/0405313. Bibcode:2004ApJ...611L..93V. doi:10.1086/423802. S2CID 14883376.
  8. ^ Young, L. M.; Lo, K. Y. (1996). "The Neutral Interstellar Medium in Nearby Dwarf Galaxies. I. Leo A". Astrophysical Journal. 462: 203–214. Bibcode:1996ApJ...462..203Y. doi:10.1086/177141.
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