Arp 171 is a pair of galaxies that appear to anchor a large cluster of galaxies located in northeastern Virgo about 375 million light years distant. Arp puts the pair in his class of galaxies with diffuse counter tails. Though I don't think he was aware of the huge plumes coming from this galaxies. In fact, I found no mention of them at all. Only the short "bright" plumes seen in his image. I think if he were aware of the huge plumes seen in my image he'd have included the entire field as it would fit within the usable field of the 200" scope. Not realizing they were there I gave this object my normal 40 minutes of luminance data. I needed several hours worth to really bring out the plumes. Still, they faintly show in my image with the larger convoluted one to the southeast and a shorter one to the northwest. The latter seems to just fade away into the background but the southeastern one ends abruptly in that direction turning back to the north-northeast.

The southeastern galaxy is NGC 5718 and is considered the cD galaxy anchoring the cluster. It is classed as S0 at NED and E-S0 at the NGC Project. It was discovered by William Herschel on April 30, 1786. It isn't in either of the Herschel 400 observing programs. The other galaxy is IC 1042 also an S0 galaxy. It was discovered by Stephane Javelle on May 28, 1891. Their S0 status probably explains why they show up as more white than the redder color of most elliptical galaxies. The only other IC galaxies in the image are IC 1041 and IC 1043 also discovered by Stephane Javelle on May 28, 1891.

In the annotated image cluster members are shown by their most common catalog number with no distance given. Non-members are shown only by distance with "G" denoting a galaxy an "Q" a quasar to the right of the object. A line to the object is used when the label had to be offset or identification would be ambiguous without the line. For purposes of determining which were cluster members I'm going with a paper that put the redshift limit for the cluster at 6824 to 8785 kps at the outside though they ended up using 8494 as the upper limit, I went with their more generous range. If a galaxy was near the limit and had a more known catalog name such as CGCG I did include both the name and distance. Just realize when this happens it may not be a cluster member.

It is likely many galaxies in the image without known redshift data are also members of the group there's no way to tell members from non-members. Some small ones are far behind the group and one is only one-fourth as far away. You need a score sheet to know who the players are it seems.

Arp's image
http://ned.ipac.caltech.edu/level5/Arp/Figures/big_arp171.jpeg

14" LX200R @ f/10, L=4x10' RGB=2x10'x3, STL-11000XM, Paramount ME