Arp’s Peculiar Galaxies
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Arp observations 21-30 of 70 total to date.
| Thumbnail | Title/link | Arp Category | Date Observed | Observer Description |
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Arp 86 / NGC 7752 and 7753 | Spiral galaxies with large high surface brightness companions on arms | 2024-09-02 20:28:00 | NGC 7753 is a barred spiral galaxy connected via a large arm/dust lane to a much smaller spiral galaxy classified jointly as Arp 86 in Halton Arp's Atlas of Peculiar Galaxies. M51, which is a famous and much larger/brighter pair of galaxies, is classified as Arp 85 in the same category. It appears that 7753's arm was distended by the gravitational pull of 7752 as it passed by from the upper left to lower right. |
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Arp 91 / NGC 5953/5954 | Spiral galaxies with large high surface brightness companions on arms | 2024-05-23 22:27:00 | Fun to be back observing Arps. These two galaxies are pretty small, but bright enough to capture even during a nearly full moon (luckily pointing to a very different part of the sky). It appears to be two galaxies merging (or at least strongly interacting during a "fly by"). NGC 5954 (left) is an elongated spiral, though it's unclear to me whether it was caused by this interaction or an earlier one. I suspect the latter since the distortion isn't obviously in the direction of its partner. On the other hand, you would need to model it: it's possible it approached from below and is in the process of avoiding merger by passing to the right. NGC 5953 (right) is a nearly featureless elliptical galaxy. It's unclear whether the third, bright object (lower right) is a star or a bright, dwarf galaxy. There's a hint of luminosity that suggests dwarf, but we're at the limits of my telescope and the night's seeing, so I'm not sure. |
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Arp 94 / NGC 3227 | Spiral galaxies with elliptical companions on arms | 2024-03-26 18:15:36 | Last observation on a full moon night before high clouds and reflected moonlight killed observing. Arp 94 appears to show two galaxies in close proximity. NGC 3227 is the much larger partner but has been greatly elongated by the encounter. Obviously, we can't tell why it's so elongated, but I presume 3226 may have nearly escaped, and shed many of its stars while passing, creating the elongated appearance. |
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Arp 101 / UGC 10164-10169 | Spiral galaxies with elliptical companions on arms | 2024-06-13 23:07:00 | The Uppsala General Catalogue of Galaxies (UGC) lists 12,921 galaxies visible from the northern hemisphere, first published in 1973. The fact that the two key galaxies in Arp 101 are listed in UGC (and not NGC or IC) underlines how obscure they are. Neither is in Astrometry.net's annotation system. We flipped our image 90° clockwise to match the orientation in Arp's catalog, which means south is up. The more southerly galaxy UGC 10164 (upper) is the "eliptical" galaxy referred to in Arp's categorization at magnitude 14.7; its spiral companion UGC 10169 is 14.9 (the spiral structure is barely evident in my capture and only slightly more clear in Arps'. The critical features are the bridge between the two galaxies and the extended tail on the spiral 10169, which are substantially fainter yet. Suggesting that the bridge between the two galaxies represents a companion "on the arm" of 10169 seems a bit of a stretch (pun intendend). During the capture in SharpCap my emphasis was on showing these connections and not worrying about the background noise or darkness. I wasn't sure if I'd be successful in capturing them, especially given there was a 50% illuminated moon during the capture. I was pleased with the result. I had to cut this observation short due to high clouds starting to trigger the brightness and FWHM filters in SharpCap. |
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Arp 104 / Keenans System | Elliptical galaxies connected to spiral galaxies | 2024-02-21 01:00:44 | This was the last observation of a very clear night, marred only by a 94% moon. I chose Arp 104 in part because I could point in the opposite direction. The key feature here is the dust lane connecting the two galaxies. Luckily it became evident after about half an hour and I was able to continue observing for a total of 60m. The featured image here was enhanced in Affinity Photo to accentuate the dust. A "natural" colored image is in the gallery. |
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Arp 114 / NGC 2300 | Elliptical galaxies close to and perturbing spiral galaxies | 2024-04-15 21:30:00 | Arp 25 (upper left) was visible from the first light frame. Arp 114's center looked like a bright star at first and capturing the rest of its disc required most of the integration time of 40m. I presume Arp concluded the two galaxies were perturbing each other because "the one heavy arm" in Arp 25 stretches outward towards Arp 114. |
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Arp 116 / M60 / NGC 4649-4647 | Elliptical galaxies close to and perturbing spiral galaxies | 2024-04-16 00:15:00 | NGC 4647 makes a lovely contrast with M60... a spiral galaxy with lots of structure vs. eliptical with virtually none other than a bright center. Certainly does appear that M60 is perturbing NGC 4647. Assuming NGC 4647 was close to circular when formed, the attraction has elongated its current shape and given the center of mass a slight kink to the south (towards M60). |
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Arp 117 / IC 982-983 | Elliptical galaxies close to and perturbing spiral galaxies | 2024-06-01 00:12:00 | Another reasonably bright Arp Peculiar Galaxy (or galaxy pair), with a large spiral galaxy (IC 983) interacting with (absorbing?) a dwarf. Essentially the spiral arms of 983 are directly connected to 982. Also, note the large, right-hand circle is a Milky Way star, not another galaxy. Surprising a galaxy as large as 983 didn't get discovered in time to be published in the NGC catalog. But this is likely because the surface brightness is a bit low, and it wasn't until photographic plates came into use that it was discovered. All NGC objects were discovered visually. The IC catalog, which was an extension of NGC was published in 1888 and 1905. IC objects were discovered both visually and with photo-plates. Anything discovered later was almost certainly discovered using photography. |
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Arp 120 / Eyes Galaxies | Elliptical galaxies close to and perturbing spiral galaxies | 2024-03-13 12:11:14 | What a fun target! The two galaxy centers are bright and were evident from the first 30 second frame. So the two galaxies "close to each other" is obvious, but it takes a while for the "perterbation" to become obvious. The extensive dust clouds connecting these galaxies are much lower brightness and took a while to become evident. Luckily it was a clear, dark night and I was able to continue integration until I judged minimal additional detail was forthcoming, after about half an hour. Very peculiar! |
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Arp 124 / NGC 6361 | Elliptical galaxies close to and perturbing spiral galaxies | 2024-06-13 23:45:00 | NGC 6361 is a straightforward target, but the tiny galaxy on its tail, MCG +10-25-3 is magnitude 15.8 and another story altogether. And, of course, the connecting dust lanes are even more obscure. BTW, the MCG catalog was based on the Palomar Sky Survey, and contains only a few galaxies above magnitude 15. Presumably this galaxy is cataloged in MCG because of its importance to Arp. Unfortunately, the evening's transparency, never very good, took a big hit after 20 minutes of integration, with a now thickened layer of high clouds shutting me down. It was tough to distinguish any connecting lane from general noise in the SharpCap capture... I processed it heavily in Affinity Photo and just managed to bring it out (note it's not terribly evident in the Palomar capture either). |