Arp’s Peculiar Galaxies
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Arp observations 11-20 of 88 total to date.
| Thumbnail | Title/link | Arp Category | Date Observed | Observer Description |
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Arp 28 / NGC 7678 | Spiral galaxies with one heavy arm | 2024-10-26 19:44:00 | This looks like a lovely, face-on spiral galaxy that is clipped a bit flat along the full length of the right side, and oddly expanded on the left. One can imagine another galaxy making a close approach to Arp 28 from the upper right, stripping off stars (though you can still see something close to Arp 28's original spiral shape in the faint dust cloud that remains). This hypothetical galaxy, as it continues past, then seems to have swung to the lower left (from our perspective) pulling open the main spiral arm of Arp 28, and drawing off more stars from the periphery. Arp categorizes this as having a single, heavy arm, though one could easily argue it has two, both on the lower left of this image. Either way, it's a lovely, intriguing target. |
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Arp 29 / Fireworks Galaxy / C12 | Spiral galaxies with one heavy arm | 2022-11-26 09:38:00 | This was literally the first, successful capture of a faint Galaxy in my EAA career. There had been a painful learning curve leading to this point: enabled by learning to capture both darks and flat frames. It was also my second attempt; two days earlier I had captured the galaxy but the focus was horribly off. This capture was my personal, "I love this!" moment. I had no notion of Arp at the time. I loved the name and wanted to be challenged. I've added to the gallery a "bonus" image of Arp 29 and the open cluster NGC 6939, imaged with my 600mm refractor in August 2023. |
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Arp 37 / M77 | Spiral galaxies with low surface brightness companion on arms | 2023-01-01 22:36:25 | This object was low in the SE skies, so i waited until the last target of the night. This is a small galaxy, and Arp's "companion on the arm" is too small, and insufficiently bright for my telescope to resolve. |
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Arp 38 / NGC 6412 | Spiral galaxies with low surface brightness companion on arms | 2024-06-12 22:59:00 | This was captured almost due north early in what is nearly the shortest evening of the year, with a 35% crescent moon due west. This is a lovely, seemingly "normal" spiral galaxy. Arp categorized it as having a "low surface brightness companion on arms" which, frankly, I would not have noticed without this prompt. On close examination, there are a couple of hints, and I infer that the glowing, slightly nebulous spot at the top (N) end of the image is a dwarf "companion" galaxy. This is consistent with the emerging bar in the center of the main galaxy, which points more or less directly at this spot. Like many "nebulae" in this part of the sky, this was discovered by William Herschel in 1797. I find the Herschel family's story inspiring and like to comment in these notes when I discover it's the case. What an amazing brother/sister/son combo they were! |
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Arp 46 / UGC 12265 | Spiral galaxies with low surface brightness companion on arms | 2024-10-26 21:33:00 | This is a truly obscure galaxy. Other than Arp, as far as I can tell, it's listed only as UGC 12265, which is the Upsala Catalog published in 1973. These are all northern hemisphere galaxies, mostly discovered at the Palomar observatory, which was Arp's home base. Arp 46 is actually the smaller (and lower) of the two galaxies you see in the image, the other being UBC 12267. I assume the "low surface brightness companion on arms" is the small bright spot (with galaxy-like halo) to the upper right (next to another bright circle, which appears to be a star within the milky way). |
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Arp 49 / NGC 5665 | Spiral galaxies with small high surface brightness companions on arms | 2024-06-07 22:22:00 | The first observation during a brief, clear window on a mostly cloudy evening during a new moon. Significantly, I was able to complete this observation at 10:22 PM on an evening when Astronomical Dusk didn't hit until 10:43. Fortunately its location in Bootes to the SSW was sufficiently far from the residual sky-glow in the NW. This is an enigmatic capture. Arp classifies it as having "small high surface brightness companions on arms", though it's far from clear to me what the companion is... in my capture (as well as Arp's), North is right. I presume the galactic center is the bright dot slightly south of center. I suppose the "companion" could be the bumps on the extreme south, though it's not clear to me that it's a separate "companion" or simply a distortion in the structure of the main galaxy. As quoted in Kanipe and Webb, Arp's notes say "appearance of wake from stellar object in E arm." Frankly I'm not sure this helps... I'm inclined to thing the "stellar object" is indeed a Milky Way star and the appearance of a wake is coincidence.... |
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Arp 71 / NGC 6045 | Spiral galaxies with small high surface brightness companions on arms | 2024-11-03 18:45:00 | On the first night of Standard Time observing, I was anxious to capture a few Arp Galaxies in Hercules, which are setting early. Arp 71 has been on my list for a while, so it was first up as soon as I achieved PA. Elevation was below 20° from the start, which makes the target vulnerable to satellite trails. If you look at the comparison shot from the Arp Atlas, developed into a positive (left hand image, believe it or not), the 200" Palomar telescope struggled with this object, so it's no wonder that my 8" Celestron did as well. NGC 6045 might be edge on, but it appears more likely to be an extreme barred spiral (SBc) where the surrounding envelope is simply too dim to show up in this image, and all we can see is the galactic center. Also suprisingly, the "high surface brightness companion" is more obvious in my image than Arp's... a dwarf galaxy hanging off the top of the bar. |
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Arp 72 / NGC 5996-5994 | Spiral galaxies with small high surface brightness companions on arms | 2024-06-13 00:49:00 | This observation principally shows two galaxies exchanging mass via a long tidal tail: the larger, NGC 5996 connecting to NGC 5994. 5996 is a barred spiral galaxy, with its bar pointing to 5994. Presumably the two galaxies passed by each other too quickly for 5996 to fully capture 5994. Instead, the interaction peeled off and elongated the eastern arm of 5996 and created the tidal exchange with 5994. While the two NGC galaxies are most noticeable, there are several additional, much smaller galaxies in the image. If you view the second image in the gallery (after the comparison to the Arp image), I overstretched it and successfully brought out an additional dust lane connecting 5996 to two additional stellar-like objects, presumably galaxies, along the western edge of the image. The original Arp image resolves a minimum of 2 additional objects, potentially several more, as the "specs" are suspiciously galaxy shaped. |
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Arp 73 / IC 1222 | Spiral galaxies with small high surface brightness companions on arms | 2024-10-28 21:40:00 | This is an attractive barred spiral galaxy, probably SBb following the Hubble classification scheme. But there's more going on here. Categorized by Arp as a galaxy with high surface brightness companions, it shows several close to the edge of the main spiral envelope: presumably the two bright objects in the upper left, the one in the lower right, and then lower left. All distort the star envelope of the main galaxy which makes it definitive that these are companion galaxies. A fifth companion may be the bright spot on the upper right edge, though it may be a star. as the impact on the envelope is unclear. The companions certainly appear to be dwarf galaxies in the middle-stages of being absorbed.... similar to M32's relationship to M31. |
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Arp 76 / M90 | Spiral galaxies with small high surface brightness companions on arms | 2024-03-13 13:32:42 | Final observation of a very successful evening, completed around 1 AM. As expected for a Messier object, it is very bright. SharpCap had difficulty plate-solving, giving a "too few stars error"... so I upped the gain to 375. Given the surface brightness, and dithering every two 30-second frames, noise stayed reasonbly under control, and I was pleased to see the structure become evident after only half an hour. |