I've not been able to find a great deal of research on this galaxy and most that I have found deals with the Seyfert aspect, not the jet. My own (probably completely wrong) theory is that a highly energetic event in some earlier era ejected a generally spherical gas shell. The jet has now caught up with the shell and is exciting a circular region where the impact is occurring. We are seeing the circular region from the side, making it appear to be an arc.
For a very deep image of this galaxy, see the Malin site at the end of the Links page. Locate the image using the NGC 4651 designation.
