NGC 4656 The Hockey Stick

[RickJ]

NGC 4656, the Hockey Stick Galaxy, is a highly disturbed galaxy or galaxies depending on who you read, located in Canes Venatici. It carries two NGC numbers, NGC 4656 which refers to the main core region and NGC 4657 which refers to the bright northeast end. While many papers through the 1980's and even a few into the 90's call this system an interacting pair most today feel it is just one highly distorted galaxy that came too close to nearby NGC 4631 and its distorted satellite NGC 4627. Its redshift puts it a bit over 40 million light-years away but most sources put it and NGC 4631 about 25 million light-years away.

This is a retake for me. I took it back when I was first getting into color CCD work. The results were very poor to put it in a good light. In this much better image it appears the northeastern end is full of massive star clusters likely triggered by the interaction with NGC 4631. Two of the massive clusters at the northeastern end and to the southwest carry separate designations as galaxies in some catalogs. Though LEDA 4546890 is designated a star cluster by NED. SDSS J124348.72+320813.8 toward the southwest end clearly resolves into a cluster of stars even in my image NED carries it as a galaxy.

Several true galaxies can be seen through NGC 4656. I was surprised the nearly detached plume far to the northeast didn't seem to carry any separate designation that I found.

While there are a lot of faint background galaxies few had redshift distances noted at NED. Those few that did are shown in the annotated image. One I happened across that seemed to be in a small group of galaxies wasn't even in NED which earned it a question mark label. In processing the image I noted a really red star below a white star north of the core of NGC 4656. It turned out to be a super red galaxy 3.8 billion light years distant. I can't recall any galaxy this red before. Other galaxies in the image even further away aren't dust reddened as much as this one. It is an IR rich galaxy, 2MASX J12440504+3217580, though such galaxies often aren't very red in the visual spectrum.

To fit the cropped image into my normal 800 pixel square many ask for I had to reduce it to 1.3" per pixel. The annotated image is an earlier process of the image and a bit darker but shows everything so I didn't redo it.

Since most post this one in a wider field with NGC 4631 I've included my latest reprocess of it as well. I'm still not happy with it but until I reshoot it this will have to suffice.

14" LX200R @ f/10, L=4x10' RGB=2x10', STL-11000XM, Paramount ME 4656
14" LX200R @ f/10, L=4x10' RGB=2x10'x3, STL-11000XM, Paramount ME 4631

Rick

[Vonstadt]

Wonderful shots, I did not know there was a 'Hockey Stick' formation like this.

I am an avid hockey player and long time fan, this was a real treat and has me looking up more info on it.

Learn something new every day, thank you for the great images.

[nubeoort]

Curious thing and form. I didn't know this, I found some info in wikipedia, and is probably a pair of galaxies, there are so beautiful, like your shots.

[RickJ]

There's a strong difference of opinion here. What is in Wikipedia is the old school view. Somewhat biased by its northeast end carrying a separate NGC designation. Today most feel this is one galaxy severely altered by interaction with NGC 4631 that I also included for this reason. It too is distorted. The object designated NGC 4657 at the northeast end is now thought to be a region of intense star formation caused by this interaction which also pulled off the north east plume. I favor this latter view though this is still open for debate most now favor the single galaxy interpretation. I can't find a paper since the mid 1980's siding with the two galaxy view. All since analyze it using the single galaxy approach that I was able to find. Why Wikipedia goes with the old interpretation without even mentioning the newer interpretation I don't understand. It usually does science better than this.

Rick