NGC 3109

NGC 3109 is a small barred Magellanic type spiral or irregular galaxy around 4.35 Mly away in the direction of the constellation of Hydra. It was discovered by John Herschel on March 24, 1835 while he was in what is now South Africa. NGC 3109 is classified as a Magellanic type irregular galaxy, but it may in fact be a small spiral galaxy. Based on the D25.5 isophote at the B-band with an angular diameter of 1,980 arcseconds, it has an isophotal diameter approximately 12.80 kiloparsecs (41,700 light-years) across, slightly larger than the Large Magellanic Cloud but smaller than the Triangulum Galaxy. If it is a spiral galaxy, it would be the smallest in the Local Group. NGC 3109 has a mass of about 2.3×10 times the mass of the Sun (M☉), of which 20% is in the form of neutral hydrogen. 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. 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 warped.