Considered the prototype of a megamaser with 98% of its emission in the infrared. In addition there is a large starburst of young stars.

Stephane Javelle found IC 4553 = J. 3-1368, along with IC 4554, on 25 Jul 1903. His position is at the south edge of Arp 220. Truman Safford made an earier discovery on 4 May 1866, but his RA for Sf. 7 = IC 1127 was 1 minute too large and Dreyer missed the equivalence IC 4553 = IC 1127. See Harold Corwin's and Malcolm Thomson's notes on this number.

400/500mm - 17.5" (4/7/89): fairly faint, almost round, even surface brightness. This is an interacting double system with an extremely faint "knot" or extension at the south end [elongated E-W on the POSS]. IC 4554 is a separate galaxy 2.2' SE of the double system observed.

600/800mm - 24" (6/16/12): fairly faint to moderately bright, fairly small, slightly elongated, uneven surface brightness and irregular appearance, though the core was not resolved into two components. Forms a pair with IC 4554 2.2' SE (not part of Arp 220 as generally assumed).

900/1200mm - 48" (5/1/19): at 375x; bright, large, contains a large uneven bright core. The halo is irregular with a hint of structure and extends mostly north of the core.

Notes by Steve Gottlieb