Arp’s Peculiar Galaxies
Page 12 of 18
Arp observations 111-120 of 171 total to date.
| Thumbnail | Title/link | Arp Category | Date Observed | Observer Description |
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Arp 220 / NGC 5421 | Galaxies with adjacent loops | 2025-07-23 14:23:54 | Arp 220 is the closest ultraluminous infrared galaxy (ULIRG) to Earth, and heavily distorted. Arp saw a bright nucleus, then wispy arms that seemed to form a loop surrounding empty space (as do the other 5 galaxies in this category of "Adjacent Loops"). However, shockingly, even my little 8" telescope could go "deeper" than Arp's image, and shows what is an extended, lower surface brightness body behind the bright nucleus. It's certainly not the 200" telescope which has several hundred times the light gathering power of my telescope. |
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Arp 224 / NGC 3921 | Galaxies with amorphous spiral arms | 2025-05-15 23:15:00 | An unexpecgted observation: forecast was mostly cloudy but it turned beautifully clear around 9 PM and stayed that way for a couple of hours. This is another William Herschel discovery from 1789. |
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Arp 225 / NGC 2655 | Galaxies with amorphous spiral arms | 2024-02-29 00:00:45 | Amorphous spiral arms indeed! They are shaped a bit like loose outer leaves of skunk cabbage, with the nucleus as flower. During capture the amorphous arms were just perceptible on my SharpCap live stack, which means that post-processing was required to make them visible in the final web images. The core and central disk are quite evident, but the arms are diaphanous. Arp's remarks also call out an absorption, the zit-like feature on the SSW (1 o'clock) edge of the nucleus: "Very faint diffuse outer arms, absorption one side of nucleus". Interesting that it's the diffuse arms he chooses to categorize. |
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Arp 227 / NGC 470 / NGC 474 | Galaxies with concentric rings | 2025-10-10 22:52:00 | This was a target for the October '25 CN EAA Challenge. NGC 474's faint but massive rings are quite a sight! Arp's recorded in his notes: " Pos. of spiral.SO is E and a little N.Very faint rings extend to diameter of 7'.4." |
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Arp 229 / NGC 507-508 | Galaxies with concentric rings | 2024-12-26 19:39:00 | NGC 507 is a large and relatively bright galaxy where the galactic disc forms discrete rings of diminishing brightness as you move away from the core. Arp remarks: "Circular or near circular rings of small density difference." This is categorized as a lenticular galaxy: more structure than a typical elliptical galaxy, but lacking the arm structure for a spiral. If you examine all of the galaxies so categorized in the Atlas (227-231), the first three (227-229) all depict a pair of galaxies, with a large, central lenticular galaxy. Confusingly, the other two (230-31) depict polar ring structures within a single, lenticular framework. |
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Arp 232 / NGC 2911 | Galaxies with concentric rings | 2025-01-26 22:18:00 | There's a conundrum here. Kanipe and Webb's book reports that Arp places this in the "appearance of fission" category. The database I created for my website which automatically looks up the Arp Category based on the Arp number (based on the AL's Arp excel list) puts this in the "concentric ring" category. The Cal Tech website providing an online version of the Atlas of Peculiar Galaxies omits Arp 232 from Figure 2 (see gallery) which is the only place where you can look up Arp's categories. For no apparent reason it skips from Arp 231 to 233. To my eye, concentric rings seems more descriptive of what I see, and is similar to Arp 229's appearance. Moreover, most of the "with fission" galaxies, starting with Arp 233, show a very distorted galactic center, usually more heavily pinched if not fully broken apart. 232's center shows a slight pinch from the SE (lower left) not nearly as dramatic as other "with fission" galaxies. Arp does call out an "Absorption lane reaching away from galaxy" which is responsible for that pinched look, and may account for Kanipe and Webb's decision. However, Arp put other galaxies with absorption lanes into "Galaxies with irregularities" so I don't think Kanipe and Webb's decision to place it into "with fission" is correct. |
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Arp 233 | Galaxies with the appearance of fission | 2024-02-21 00:00:35 | This is a tiny object which stresses the limits of my 8" SCT with 294 sensor. Frankly, the 18m of integration was totally inadequate. I was new to this and clearly didn't know what I was doing. That said, the "appearance of fission" is tough to see, even in Arp's imagery, and I'm not sure even a few hours with my equipment would suffice. I've taken my best shot at identifying the fission in image #2 using Arp's plate. As well, Arp remarks, "Narrow faint absorption lane in SE direction". This makes another subtle appearance on Arp's plate which I illustrate in image 3. |
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Arp 234 / NGC 3738 | Galaxies with the appearance of fission | 2025-01-03 22:37:00 | Because of its irregularity, this is a very challenging object to interpret. "The appearance of fission" presumably suggests the galaxy is breaking apart. Yet Arp's remarks suggest, "Considerable resolution into stars and absorption tubes", Absorption tubes I can somewhat understand. There do seem to be dark veins running along the surface. They're more clear in Arp's (Oh, what I would give for a 200" telescope and clear mountain air"), but you can see corresponding veins in my capture. But fission? I don't see anything here that suggests fission. Indeed, current consensus is that this is an area of active star-birthing. See: https://esahubble.org/images/potw1243a/ |
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Arp 235 / NGC 14 | Galaxies with the appearance of fission | 2024-10-26 22:22:00 | This is a puzzling galaxy with what looks like at least 2, and possibly 3, elliptical galactic nuclei at slightly different orientations. The result is a galaxy with a much larger and more elongated, irregular center than normal. Arp categorizes this as having "the appearance of fission", and I suppose that's possible if you thought that there exists a mechanism for fission. Arp believed in galactic fission... but it runs totally against mainstream cosmology. Mergers seem like such a simpler explanation, and Occam's Razor applies in my mind. I certainly think that incomplete fusion is the simpler explanation of the appearance here. I did give Arp the benefit of the dark here. To my mind the plate is overexposed, so I worked on it and "developed" a positive image to see if there was something I was missing. Arp does call out the "faint outer oval" in his notes, and I tried to enhance the positive view of the plate to provide a balanced appearance. I did notice two, low surface brightness companions, close by, SW of the disk. Does that change the argument? Not in my mind. |
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Arp 238 / UGC 8335 | Galaxies with the appearance of fission | 2025-07-30 22:30:00 | Welcome to the "Way Back Machine" where Arp suggests this target provides "the appearance of fission," i.e. looking like a single galaxy pulling itself into two. This is another example of the reluctance to suggest a merger. In part through the examples provided by Arp, the astronomy-world began to understand that mergers were common events in the evolution of most major galaxies. |