For my return to Arp galaxies here's another twofer deal.

Arp 51 and Arp 144 are only a few minutes of arc apart in the sky though they are likely very far apart in light years, it is likely just our view angle that makes them appear close. Arp 51 is the spiral galaxy while Arp 144 is the weird pair of galaxies in the center. But since I can find no red shift data for Arp 51 this is only a guess on my part. In fact I find very little on it at all. Arp classed it under Spiral galaxies with companions on arms: Small, high surface brightness companions. Apparently he was referring to the blob that seems to "straighten" the spiral arm that goes nearly straight east at the top of the core. It then turns south at the object. It likely is a different galaxy but could just be a knot in a kinked arm. Without red shift data it is hard to say. The only paper I found on it calls it an "object" and never does try to determine what it is.
Arp's photo is at: http://nedwww.ipac.caltech.edu/level...ures/arp51.gif

The other Arp object is Arp 144 in the center, comprised of two galaxies, NGC 7828 and NGC 7829. The former is the very weird blue object while the latter is the galaxy to the south east (lower left). The pair is about 246-249 million light-years away. Arp classed it under Elliptical and elliptical like galaxies: Material emanating from elliptical galaxies. Today both are considered to be Ring galaxies with NGC 7828 Ring B and 7829 being A. The modern classification of NGC 7828 (the one on the right) is an Irregular galaxy of the Magellan class that's peculiar (Im pec) to use the nomenclature. The other is classed as S0 pec. It is peculiar probably because of all the tidal spray from the interaction. NGC 7828 pretty much defies all rules about galaxies. It looks more like a Star Trek type space ship than a galaxy. Obviously the interaction has changed it. I could make the argument it looks like two galaxies itself. I'd like to see spectroscopic data on its rotation curve(s). But there is virtually nothing on this pair in the literature. One paper does say: "The spiral or a pair of galaxies are perturbed by a compact elliptical galaxy." So they too are considering the double galaxy idea for NGC 7828 but never decide which it is.

My photo is rather blurry as this pair is located at -13 degrees declination, too far south for good seeing at my location. In Arp's photo http://nedwww.ipac.caltech.edu/level...ig_arp144.jpeg the blue arcs in my shot are seen to be massive star clusters I was unable to resolve that low in the sky. In fact the whole object looks rather different in his blue light photo than mine that includes all of the visual spectrum. Not all this difference is due to seeing. I find only a couple other photos of this object on the internet but they do show it looking more like my shot than Arp's.

The asteroid in the image is (16506) 1990 UH1 at magnitude 17.1. This area of the sky is rather poorly surveyed so I was unable to find much on other galaxies in the image, most of which are anonymous due to lack of survey data being taken on this part of the sky. There is an interesting trio of galaxies directly west of Arp 144. Left to right they are LEDA 938317, 2MASX J00055623-1324178 and APMUKS(BJ) B000321.75-134134.3. I have no distance data on any of them. In fact there's no distance data available on anything in the image except Arp 144. The reddish galaxy in the lower right corner is LEDA 9367795. Below it and a bit left near the bottom edge are two blue galaxies LEDA 397 and 398 right to left. Arp 144 is at the west end of the constellation of Cetus the whale.

Color data was limited as it was getting too low that night for more color data. After that clouds and moon conspired until it was too late in the season. I have only a small window of opportunity for objects this low unfortunately. It was binned 3x3 which helped some but color is weak and noisy.

14" LX200R @ f/10, L=4x10' RGB=1x10', STL-11000XM, Paramount ME

Attached image has been cropped. Displayed at the full 1" per pixel image scale.

Full image:
http://www.spacebanter.com/attachmen...tid=2449&stc=1

Rick

Attached Images

ARP144L4X10RGB1X10X3CROP.jpg (82.2 KB, 22 views)

Thanks again Rick for your detailed photos and analysis. At -13 degrees this is a long way South for you. Great capture.

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Kind regards
Matt
LXD75 SN 8" f/4, DSI II pro

The most exciting phrase to hear in science, the one that heralds new discoveries, is not Eureka! (I found it!) but rather, "hmm.... that's funny...."
Issac Asimov

Hello Rick:
Very well done.
They are objects very distant, and very difficult to photograph.
Many greetings
Cesar

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Another fine Arp image with great info and comparising. Thanks Rick and Clear Skies.