This galaxy is similar in nature to the Milky Way'ssatellite galaxy, theLarge Magellanic Cloud (LMC),[6] though is not as bright nor as large. NGC 4449 has a general bar shape, also characteristic of the LMC, with scattered young bluestar clusters.
Photos of the galaxy show the pinkish glow of atomic hydrogen gas, the telltale tracer of massive star forming regions.
NGC 4449 is surrounded by a large envelope ofneutral hydrogen that extends over an area of 75arc minutes (14 times larger than the optical diameter of the galaxy). The envelope shows distortions and irregularities likely caused by interactions with nearby galaxies.[11]
Interactions with nearby galaxies are thought to have influenced star formation in NGC 4449 and, in fact, in 2012 two small galaxies have been discovered interacting with this galaxy: a very lowsurface brightness disrupteddwarf spheroidal with the same stellar mass as NGC 4449'shalo but with a ratio ofdark matter to stellar matter between 5 and 10 times that of NGC 4449[12] and a highly flattenedglobular cluster with twotails of young stars that may be the nucleus of a gas-rich galaxy.[13] Both satellites have apparently been disrupted by NGC 4449 and are now being absorbed by it.[12][13]
At least oneultraluminous X-ray source (ULX) is known in NGC 4449, called NGC 4449 X7. There are three candidates that have been identified as optical counterparts to NGC 4449 X7 (i.e. they may be associated with the ULX). They are all early (B-type toF-type)supergiants that are estimated to be about 40 to 50 million years old and about 8 times the mass of theSun.[14]
^R. W. Sinnott, ed. (1988).The Complete New General Catalogue and Index Catalogue of Nebulae and Star Clusters by J. L. E. Dreyer. Sky Publishing Corporation and Cambridge University Press.ISBN978-0-933346-51-2.
^Bajaja, E.; Huchtmeier, W. K.; Klein, U. (1994). "The extended HI halo in NGC 4449".Astronomy and Astrophysics.285:385–388.Bibcode:1994A&A...285..385B.
^abMartínez-Delgado, David; Romanowsky, Aaron J.; Gabany, R. Jay; Annibali, Francesca; et al. (2012). "Dwarfs Gobbling Dwarfs: A Stellar Tidal Stream around NGC 4449 and Hierarchical Galaxy Formation on Small Scales".The Astrophysical Journal Letters.748 (2): L24.arXiv:1112.2154.Bibcode:2012ApJ...748L..24M.doi:10.1088/2041-8205/748/2/L24.S2CID54890773.
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