Monday, 6 April 2015
Deep Sky column 3/2015: The three phases of galaxy mergers
Second phase in galactic collision - NGC 4676A & NGC 4676B (Mice Galaxies): Galaxies visible with 8 inch Orion DSE, both galaxies of same size and brightness. Failed to spy with 4.5" SkyQuest. "Tails" commonly described as being difficult to observe, NGC 4676A's tail has been seen with 12 inch telescope. Pair discovered by William Herschel in 1785. IC designations (819 & 820) from Rudolf Spitaler (1849 – 1946).
Third phase in galactic collision - NGC 4038 & NGC 4039 (Antennae Galaxies): Beaten up, tormented shape. 400 million years from now the two will merge as a giant elliptical galaxy. Southern "tail" is 10' long with the northern one being at least 7'. Brightening in southern tail is NGC 4038S - a presumed Tidal Dwarf Galaxy (TDG). Visually NGC 4039 is smaller and fainter. Both components have fairly faint surface brightness. Brightest H II regions are roughly magnitude 15 and within reach of medium to large apertures.