Arp 120 is better known as The Eyes or NGC 4438 with NGC 4435 bottom to top. They are part of the Virgo Galaxy Cluster located some 60 million light-years away. Arp's classification of this one is under Elliptical and elliptical-like galaxies: Close to and perturbing spirals. The only problem is NGC 4435 is not perturbing NGC 4438 as Arp thought. It does have a large halo about it, the full extent not seen in my shot but it is very symmetrical and shows no hint of distortion. They have two very different redshift values. So different that if they did interact it was over almost before it started. So if NGC 4435 isn't the culprit who is? One possible answer I've seen is that NGC 4438 could be the result of a merger that's already happened and the debris hasn't as yet returned to the galaxy. The multiple planes of dust lanes near the core would argue for this, the fact only one core can be seen at all wavelengths would argue strongly against it, however. There things stood until last year. I missed it in fact. Glen Youman pointed out the correct solution to me. Seems the culprit is the big gorilla in the cluster -- M86! That's its glow coming in at the lower right. I cleaned up the image too much. I thought it had a gradient that was really hints of the connection to M86. I tried reprocessing but without H alpha data it just didn't work. For more information on this see: http://www.noao.edu/outreach/press/pr08/pr0807.html#images

The tidal cloud about NGC 4438 must be very thin however and contain little dust. Notice the reddish object in the darker triangular area north of the bright part of the galaxy. This isn't a foreground star but the distant galaxy SDSS J122746.38+130229.4 which is about 1.6 billion light-years distant. To be seen through the tidal plume at that great distance the plume must be very sparse and consist mostly of widely spaced stars with little dust and gas. Another galaxy is seen in the galaxy but may be in front of NGC 4438. It is the obvious elliptical just below the brightest part of the galaxy at the edge of the main halo and east of the tidal plume. It is VCC 1040 and has a blue shift so is moving toward us. It is classed as a dwarf elliptical and shows the wide variation of redshift to be found in this galaxy cluster.

Most class NGC 4435 as SB0 and NGC 4438 a mess. No two seem to agree. The NGC Project just says S... while NED says SA(s)0/a pec. NED says both are LINER galaxies. The two were discovered on April 8, 1784 by William Herschel. Both are in the original Herschel 400 program. My notes from April 20, 1985 taken on a fair-humid night at 50x read: NGC 4435 "Small, galaxy with a bright center. Somewhat elliptical. Forms a tight double with NGC 4438, 6 other galaxies seen in the same one degree field of view." NGC 4438 "Large, highly elongated galaxy with very large irregular halo that stretches nearly to NGC 4435. M 84, M 86 NGC 4402, NGC 4413, NGC 4425 and NGC 4435 are all in the same one degree field of view."

Then there's the rather peculiar galaxy to the northwest of Arp 120, the very blue IC 3355. SDSS gives it three separate numbers. A note at NED says;"Faint not disrupted progenitor. In its tail 3 diffuse companions in a blue haze." I can't find the third one, however. IC catalog considers it just one irregular Magellanic galaxy. It has a redshift similar to that of NGC 4435.

In the annotated image galaxies that are members of the cluster are identified by name but no distance is given as they are all about 60 billion light-years give or take 10 million or so. Exact distances are hard to determine since the velocities of member galaxies can vary greatly making red shift a poor distance indicator. Those with redshifts that put them far beyond the cluster are noted by their distance in billions of light-years. Several quasars out to past 11 billion light-years are noted. Some galaxies I can't determine any distance for but may or may not be cluster members are identified by name with a "?" to indicate this uncertainty. In all cases no redshift data was available. You will note that sometimes a cluster galaxy is right beside a distant galaxy but telling which is which without the labels could be difficult.

I took this data several years ago. Due to clouds I never did redo it as intended. Seeing was very poor and I was using a focuser that wasn't up to the job. The result is limiting magnitude is about 21.2 instead of my normal 22.5 and detail is a bit lacking due to 4" seeing. Maybe this spring I can redo it with a lot more data to get far more of the halos around both galaxies. Also, I pushed the color more than normal to bring out the subtle color differences in the plume. This caused IC 3355 to turn super blue. Indicating it has really massive star formation going on and may be more interesting than Arp 120.

Arp's image:
http://ned.ipac.caltech.edu/level5/Arp/Figures/big_arp120.jpeg

14" LX200R @ f/10, L=8x10' RGB=2x10', STL-11000XM, Paramount ME