Harold Corwin

IC 4553 = IC 1127, and IC 4554. In the recent astronomical literature, the two numbers IC 4553 and IC 4554 are usually applied to the single peculiar galaxy Arp 220 = IRAS 15327+2340. The object has two optically bright "nuclei" or knots, so it has been assumed that one IC number applies to each (the real nucleus, a strong infrared source, is actually hidden optically behind the dust lane that splits the optical image of the galaxy; it does however show through in the near-infrared. See the Pan-STARRS image for a vivid show!).

However, the IC positions are from careful micrometric measurements by Javelle. That for IC 4553 is close the the GSC position for Arp 220, so that identification is secure. But Javelle's position for IC 4554 is 2.2 arcmin southeast of IC 4553, much too far from his position for IC 4553 to be the other of the optical knots. Exactly at the position given by Javelle, however, is a somewhat fainter galaxy. It matches Javelle's description, and there is no doubt that it is the real IC 4554.

One other curiosity about this field: Javelle was not the discoverer of IC 4553. It was actually found in 1866 by Safford, and is IC 1127 (which see).

― IC Notes by Harold Corwin

Harold Corwin

IC 1127 = IC 4553. Just one minute of time east of IC 4553 (which see), and an arcmin south, lies the IC position for I1127. There is nothing at all in this position, though there are 2 or 3 very faint stars just to the north. I1127 was found in 1866 by Safford at Dearborn Observatory, and was first listed in an appendix to the NGC as Safford 7. Dreyer later included these appended objects in the first IC, where this one received the number 1127.

Safford's positions are only approximate, having been determined simply by centering the object in the field, then reading the setting circles. Thus, they are often merely indicative and also seem to suffer from digit errors now and then (IC 200 is another example, with its RA being 2 minutes of time off). Since Safford's description (pF) is correct, IC 4553 is almost certainly the object which he saw.

― IC Notes by Harold Corwin

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