Arp’s Peculiar Galaxies
Page 8 of 11
Arp observations 71-80 of 110 total to date.
| Thumbnail | Title/link | Arp Category | Date Observed | Observer Description |
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Arp 205 / NGC 3448 | Galaxies with material ejected from nuclei | 2024-04-22 23:10:00 | I struggled with Arp 205, because it's hard to know why this target is categorized as containing "material ejected from nuclei". What does that look like? Arp left no comments that might offer insight. Technically, it's doubly tough because you have a mix of high and low surface brightness objects: I tried my usual grayscale and inversion tricks here. Despite the normal infirmities of OSC imaging, color helps more than you'd expect, and I couldn't improve on my original color captures. Describing the bright object from the bottom left to upper right (NW to SE) NGC 3448 (discovered by William Herschel in 1789.) looks more like two galaxies, not one. There are clearly two galactic nuclei here associated with spiral disks. The first disc is foreshortened, at a different plane from the second, enlongated., Then there's a 3rd spiral disk, tucked in where the brightness ends, at yet another angle, a tiny nucleus, and despite low brightness, showing up as a gray disk against the green/black background. Finally there's the smudge towards the SW corner, disconnected from the other three. I can't see much of it, but what I can see has the distinctive shape of a S barred spiral center. From a modern perspective you know that it's UGC 6016, and a cataloged 17th magnitude galaxy. Arp, of course, didn't have that advantage, but his plate shows the galaxy pretty clearly, even if it's surrounded by other junk, That leaves only the tail NE of NGC 3448 (lower left), which is shown very clearly in Arp's plate, and which my image only hints at. Could that be ."ejected material"? But how is that different from a narrow filament? And why does that trump 4 galaxies interacting together as a reason for peculiarity? |
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Arp 206 / NGC 3432 | Galaxies with material ejected from nuclei | 2024-04-21 23:15:00 | Arp 206 consists of an edge-on spiral galaxy (NGC 3432) of magnitude 11.3 interacting with a magnitude 16.3 galaxy, UGC 5983 (the little smudge slightly higher than the lower edge of 3432's disk, i.e. SW from the center or NW from the edge). A more likely candidate for "material ejected from nuclei" is the material to the NE (upper left}. At least it's ub the same plane. And the NE end of the central disk looks disrupted. But what suggests it's an ejection and not a merger? |
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Arp 210 / NGC 1569 | Galaxies with irregularities | 2024-02-29 00:00:37 | The long axis of this galaxy is oriented from SE (upper left) to NW (lower right). I suppose you could describe it as a barred spiral, but in a "normal" barred galaxy you'd expect a single, central bright nucleus, whereas Arp 210 exhibits 5 bright spots within the "bar". Three are in a line close to the SE end. The fourth is rotated SSE from the third spot. The fifty, final bright spot is close to the NW end, continuing the line of the first three after a long gap. The central bulge appears slightly bent on the z axis, with a slight kink -- down and up -- at the second bright spot, and a distinct bend between the third and the final spot. The NW (lower right) hemisphere disk appears thick and intact. The SE hemisphere appears to have been disrupted. Irregular indeed! It certainly gives the impression of a spiral galaxy that has incompletely absorbed a number of smaller galaxies. |
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Arp 212 / NGC 7625 | Galaxies with irregularities | 2024-10-26 20:03:00 | Arp remarks: "Narrow chaotic absorption tubes across one end". I had to look up "absorption tube" and I'm not sure I found the correct answer. The term can describe the phenomenon where light from a distant galaxy passes through a cooler gas cloud, causing specific wavelengths of light to be absorbed, creating "absorption lines" on the galaxy's spectrum. Presumably this refers to the white tubes in the inverted images which are mostly on the S end of NGC 7625. These are consistent with a cooler feature (will be darker in reality). It was easier for me to sharpen the image in inverted space, and the reason why the featured image is inverted. Anyway, even though it's quite small, this target was engaging and beautiful. This was my third outing with my new, Player-one Apollo-Mini monochrome camera and I started feeling comfortable with it. While occasionally color helps interpret an image, much more often the greater sensitivity of the mono camera makes for a more detailed image, as in this case. |
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Arp 213 / IC 356 | Galaxies with irregularities | 2024-02-29 00:00:41 | This is a beautiful, bright spiral galaxy, slightly elongated. Normal to the casual astronomer. Unless you read Arp's remarks: "Faint straight absorption lanes lead toward nucleus, become triple". What is an absorption lane? I believe it's a cool (darker) dust lane that obscures some of the light emanating from the galaxy, absorbing specific wavelengths and creating "absorption lines" on the galaxy's spectrum. Can I see it on the image? Yup. If you look for it, it shows up clearly in Arp's capture as a light feature. In my color image it shows up as a slightly darker-brown feature from the edge of the disk in the NW (upper left) towards the center.As it approaches the nucleus, it forks into at least two prongs (and 3 in Arp's higher resolution image). If the galaxy were an eyeball, this dust lane would make it appear slightly "bloodshot". The second image in the gallery shows two color views of the galaxy, where the color balance is shifted slightly to improve the absorption lane's visibility, and where a second image shows arrows to locate the feature explicitly. I did not take notice of this until I went looking for it, triggered by Arp's remarks. Who knew it made the galaxy peculiar? |
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Arp 214 / NGC 3718 | Galaxies with irregularities | 2024-04-16 21:30:00 | Arp's remarks speak volumes: "Barred spiral, sharp nucleus, narrow absorption lanes through center." When I originally captured this, I was unaware of Arp's remarks, and completely missed the key feature: the absorption lanes. I thought it was the arms. This is a striking target worth revisiting. Was enjoying watching the image build until a wall of clouds stopped the observation, hence the short capture time. That said, despite the short integration time, the lanes are strikingly evident. |
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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 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. |