THE OPTICAL MORPHOLOGY OF THE KINEMATICALLY PECULIAR GALAXY NGC-4826

We present CCD BVI photometry of the galaxy NGC 4826, the Evil- or Bla ck-Eye galaxy, which was recently found to have two counter-rotating g as disks. We study the extinction in the inner gas disk, which gives N GC 4826 its nickname, and find that this disk can be coplanar or close to coplanar with the stellar disk and still cause the strong absorpti on that is seen on one side of the galaxy. We try to constrain the ori entation of the outer gas disk by looking for a small overall asymmetr y in the light distribution which would be present if there is dust in this disk, and if it is significantly tilted with respect to the main body of the galaxy. The test shows that the light distribution does n ot preclude the outer gas disk from being coplanar with the stellar di sk as well. NGC 4826 has a small bulge, with a bulge to total light ra tio of 0.17 in B. We confirm that this galaxy is indeed a spiral, with a perfect exponential disk down to 27 mag arcsec-2 in B. The close to coplanar orientation of the gas disks is one aspect which is in good agreement with what is expected on the basis of a merger model for the counter-rotating gas. The rotation direction of the inner gas disk wi th respect to the stars, however, is not. In addition, the existence o f a well defined exponential disk probably implies that if a merger di d occur it must have been between a gas-rich dwarf and a spiral, not b etween two equal mass spirals. The stellar spiral arms of NGC 4826 are trailing over par-t of the disk and leading in the outer disk. Recent numerical calculations by Byrd et al. for NGC 4622 suggest that long lasting leading arms could be formed by a close retrograde passage of a small companion. In this scenario, the outer counter-rotating gas di sk in NGC 4826 might be the tidally stripped gas from the dwarf. Howev er, in NGC 4826 the outer arms are leading, while it appears that in N GC 4622 the inner arms are leading. A realistic N-body/hydro simulatio n of a dwarf-spiral encounter is clearly needed. It may also be possib le that the counter-rotating outer gas disk is due to gradual infall o f gas from the halo, rather than from a discrete merger event.