NGC 3109

spiral galaxy in the constellation Hydra

NGC 3109 is a small barred Magellanic type spiral galaxy or irregular galaxy around 4.34 million ly away in the direction of the constellation of Hydra. NGC 3109 is believed to be tidally interacting with the dwarf elliptical galaxy Antlia Dwarf.[1] It was discovered by John Herschel on March 24, 1835 while he was in what is now South Africa.[2]

The Purple light in the photo shown is the galaxy.

Size and morphology


NGC 3109 is classified as a Magellanic type irregular galaxy,[3] but it may in fact be a small spiral galaxy. If it is a spiral galaxy, it would be the smallest in the Local Group.[4] NGC 3109 has a mass of about 2.3×109 times the mass of the Sun, of which 20% of the mass is in the form of neutral hydrogen.[5] It is oriented edge-on from our point of view, and may contain a disk and a halo. The disk appears to be composed of stars of all ages, whereas the halo contains only very old and metal-poor stars.[6] NGC 3109 does not appear to possess a galactic nucleus.

From measurements of the neutral atomic hydrogen in the galaxy, it has been found that the disk of NGC 3109 is twisted. The distortion has the same radial velocity as gas in the Antlia Dwarf galaxy, showing that the two galaxies had a close meeting about 1 billion years ago.[7]


  1. Grebel, Gallagher, Harbeck, p.7
  2. "SEDS USA". SEDS USA. Retrieved 2022-11-11.
  3. Aparicio, A.; Herrero, A.; Sánchez, F. (1998-06-13). Stellar Astrophysics for the Local Group: VIII Canary Islands Winter School of Astrophysics. Cambridge University Press. ISBN 978-0-521-63255-3.
  4. Sauvage, Marc; Stasinska, Grazyna; Schaerer, D. (2002-07-31). The Evolution of Galaxies: II - Basic Building Blocks. Springer Science & Business Media. ISBN 978-1-4020-0622-7.
  5. Bergh, Sidney (2000-05-15). The Galaxies of the Local Group. Cambridge University Press. ISBN 978-1-139-42965-8.
  6. Hidalgo, Sebastian L.; Aparicio, Antonio; Gallart, Carme (2008-12-01). "The Disc-Halo Structure of NGC 3109". The Astronomical Journal. 136 (6): 2332–2342. doi:10.1088/0004-6256/136/6/2332. ISSN 0004-6256. S2CID 121654769.
  7. Barnes, D. G.; de Blok, W. J. G. (2001-06-25). "On the Neutral Gas Content and Environment of NGC 3109 and the Antlia Dwarf Galaxy". The Astronomical Journal. 122 (2): 825–829. arXiv:astro-ph/0107474. doi:10.1086/321170. S2CID 15734118.