Object name: ARP042
Designation(s): ARP042, HCG73,
Arp 42/NGC 5829 and IC 4526 falls under Arp's category of spiral galaxies with a low surface brightness companion on an arm. Though in this case, I can't see that the companion is on a spiral arm nor that it is of low surface brightness. It seems rather bright in my image. The wrap around arm is very faint, however. The pair is located in the constellation of Bootes about... Houston we've had a problem. Seems the red shift distance to NGC 5829, the nice spiral is 265 million light-years but the "companion" has a redshift distance of 620 million light-years according to NED. If correct, it isn't a companion at all but a distant background galaxy. Adding to the confusion is that both are members of the Hickson 73 galaxy group. This is described in a note at NED as: "Hickson 73 - Group is actually formed by a bright low redshift galaxy - detected also at radio wavelengths - plus an accordant triplet at much higher redshift. Galaxy e is a background object." These 5 galaxies are noted on the annotated image with the prefix 73 and the Hickson letter followed by its redshift distance. Why the 6th blue galaxy at the distance as NGC 5829 isn't included in the group I don't know. It would seem worthy of inclusion. The galaxy was discovered by Édouard Stephan on May 11, 1882.