Arp’s Peculiar Galaxies
Page 13 of 18
Arp observations 121-130 of 171 total to date.
| Thumbnail | Title/link | Arp Category | Date Observed | Observer Description |
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Arp 239 / NGC 5278-5279 | Galaxies with the appearance of fission | 2025-08-27 22:54:00 | Two, reasonbly bright NGC galaxies pretending they're M-51. There's an obvious connection from 5278, the larger galaxy, to 79 via a heavy arm. Less obvious connection between the two nucleii. |
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Arp 240 / NGC 5257 and 5258 | Galaxies with the appearance of fission | 2025-07-21 22:16:00 | Arp categorizes this pair of interacting galaxies as providing "the appearance of fission". You can see why... two elongated galaxies roughly the same size, roughly mirroring each other. The best telescope in the world renders them with little internal structure visible. Could they have been, originally, one galaxy, somehow split apart? Continuing to share stars and other matter as they continued to separate? Possibly. At the time, galaxy mergers were thought nearly impossible due to the immense distances involved. So "fission" -- even absent any theoretical framework -- seemed a valid possibility. And welcome to the mid-1960s when some of the best observers in the world -- using the best telescopes in the world -- were seeing these phenomena for the first time and struggling to figure them out. |
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Arp 242 / NGC 4676 / Mice Galaxies | Galaxies with the appearance of fission | 2025-03-26 01:00:00 | We're seeing two small spiral galaxies approaching a merger. The "tails" are tidal tails... the closer ends of the galaxies experience much greater gravitational attraction than the far ends. As the galaxies move towards each other, the far ends leave behind some stars. Arp didn't believe in galaxy mergers which seems strange today. He notes "Very thin, bright tail from north nucleus which has strong absorption," but categorized the peculiarity as the "appearance of fission". How two perfectly formed spiral galaxies could be established from a "fission" seems so much more complicated than the modern consensus that galaxy mergers are commonplace. Arp was observing phenomena which few other astronomers were paying attention to -- indeed he was paddling upstream against the orthodoxy that was trying to identify regularities, not peculiarity. Bottom line, in this case, I think his "fission" idea is dead wrong. But given the state of knowledge at the time, the phenomena were worth pointing out even if the implied explanation was incorrect. A fun capture on a clear night with crummy seeing as evidenced by every visible object twinkling noticeably. |
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Arp 244 / Antennae Galaxies / C60 | Galaxies with the appearance of fission | 2024-05-02 22:17:00 | Discovered by William Herschel in 1785, and included in Halton Arp's "Atlas of Peculiar Galaxies". This is an entertaining target showing two bright galaxies in an intimate embrace, with a long narrow filament extending behind, and appearing to terminate at a tiny dwarf galaxy. The filaments are quite evident in the color image; if you can't see them, please boost the brightness on your monitor and zoom into the image. Fission or merger I suppose are symmetrical notions, so one can draw either conclusion from the heavily distorted structures; somewhat evident in NGC 4038 (right), and largely destroyed in 4039. While the notion of a merger is well accepted now, Arp usually interpreted galaxies as breaking apart or ejecting matter. Hence his categorization of these "with the appearance of fission". I remain skeptical though admire his contrarian spirit. |
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Arp 244 / Antennae Galaxies / C61 | Galaxies with the appearance of fission | 2024-05-02 22:17:00 | See C60 for writeup. |
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Arp 245 / NGC 2992 / NGC 2993 | Galaxies with the appearance of fission | 2026-03-08 21:00:00 | Another case where my monochrome CMOS camera is capable of capturing a deeper image than Arp's 200" using Emulsion D (the "standard" emulsion). "Very faint diffuse connection from both ends of N spiral to S spiral" aren't so faint in my capture, likely the result of longer wavelength emissions through near-IR. Appearance of fission? Arp abhorred what he called "merger mania" and rarely interpreted interacting galaxies as merging. Still, it appears more likely a merger in process than "fission". |
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Arp 262 / UGC 12856 | Galaxies with irregular clumps | 2024-10-28 22:53:00 | Arp classified this object into "Galaxies with Irregular Clumps". His remarks add, "Some resolution into knots." Both statements are true enough: on the N (top) end it does resolve into knots. It's all a bit surrealistic, like Salvador Dali's clock in The Persistence of Time. While I don't understand the details, Arp was personally invested in the idea that galaxies didn't merge in order to explain interactions he perceived between galaxies of different red shifts. From the little I've read, the argument swung on the "probabilities" of distant galaxies aligning visually by chance. This strikes me as deeply flawed, since there's a selection bias working in the other direction: it's particularly odd in cases like this observation where the visual evidence of merger seems so compelling. In the middle, there's a nearly intact spiral. At the S end, a high-brightness spiral dwarf appears to be in the process of merging, moving in at a more extreme NE to SE tilt. The bend in the middle is a reaction to the relative motion. |
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Arp 263 / NGC 3239 | Galaxies with irregular clumps | 2025-04-18 00:12:00 | Arp categorizes this as a galaxy with irregular clumps, and notes, "Diffuse outer filaments, bright knots inside." It certainly has all of that. The modern consensus seems to be that this is a post-merger galaxy that hasn't yet fully assimilated its quarry. Started observing this after transit. As it descended, the lowering angle made it more susceptible to cloud cover. I eventually had to give us with less than 30m. |
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Arp 264 / NGC 3104 | Galaxies with irregular clumps | 2026-03-09 21:21:00 | This is an irregular galaxy, listed as apparent visual magnitude of 13.2. This is another instance where the sensitivity of my CMOS camera trumps the 200" telescope imaging on spectrographic film in terms of sensitivity. The 200" gathers 625x as much light as my 8", but the film was so insensitive!. I had to give my image more space in the side by side comparison with Arp's. The stars align perfectly, but my sensor rendered the shadowy exterior so much more fully that the N and S ends of the galaxy would have been truncated if I'd followed Arp's cropping. |
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Arp 266 / NGC 4861 | Galaxies with irregular clumps | 2026-03-01 23:37:00 | Even though this galaxy resembles a inchworm, it is profoudly unusual. Note the galactic center is at the bottom of the frame; the bright spot at the other end is a superimposed star. What created such a bizarre shape? I certainly can't say. Even the Hubble image doesn't tell you very much. |