Arp’s Peculiar Galaxies
Page 4 of 11
Arp observations 31-40 of 110 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 connecting SW (rotate clockwise from N to W) via a large arm/dust lane to a much smaller spiral galaxy NGC 7752. This certainly qualifies as a "high surface brightness" companion. It is, however, the only, obvious bright companion and begs the question why there appear to be two other extended filaments emanating from NGC 7753 (see inverted image in the gallery). Are these filaments explained by low brightness companions? Possibly. One extended filament curves NE (upwards and right) on from the top of 7753's disk towards two bright circles. Those are almost certainly Milky Way field stars, and not involved gravitationally at all. It's possible the upper arm is simply maintaining rotational symmetry with the lower arm ( I don't understand the physics well enough to know if that's possible). Alternatively, there are hints of low surface brightness companions: one located between the two field stars just described, and the other just W (below). In addition, an extremely faint filament continues to the WNW (down and slightly right). This connects to a tiny smudge of a possible galaxy roughly level with the bottom the compact spiral disk of NGC 7753. Visually, the curve is continued by the line of field stars paralleling SW back towards 7752, but I DO NOT believe any continuous filament connects them there. |
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Arp 89 / NGC 2648 and PGC 24469 | Spiral galaxies with large high surface brightness companions on arms | 2025-01-26 23:35:00 | There's no doubt that NGC 2648 enjoys a "high surface brightness companion" in PGC 24469. Not so bright, however, that William Herschel saw it when he discovered NGC 2648 in 1784. It's not listed in the IC catalog, so presumably wasn't observed until some time during the 20th century. The inverted image clearly shows a direct connection, implied as well by the slight "integral sign" shape of NGC 2648 from what presumably started as a classic spiral galaxy. |
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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 | NGC 5954 and 5953 are pretty small, but bright enough to capture even during a nearly full moon (luckily pointing to a very different part of the sky). They appear to be merging (or at least strongly interacting during a "fly by"). NGC 5954 (left) is an elongated spiral, though it's unclear to me whether the elongation was caused by this interaction or an earlier one. I suspect the latter since the distortion isn't obviously in the direction of its current partner. NGC 5953 (right) is a nearly featureless elliptical galaxy. Arp's remarks, "Broad pec. arm to comp., then absorption: faint extension from comp," accurately describes the connection and suggests they saw one companion. I debated whether there might be two, dwarf galaxies interacting with the primary pair. Both bright objects (SW, lower right, NW, upper right), I continue to interpret as field stars distorted by poor seeing rather than galaxies. |
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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, spiral partner that has been greatly elongated by the encounter. Obviously, we can't tell why it's so elongated, but I presume the ellliptical galaxy, NGC 3226 may have nearly escaped, and shed many of its stars while passing, creating the elongated appearance. The exchange of stars is evident in the extensive dust cloud connecting the two galaxies, best viewed in the inverted image. |
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Arp 99 / NGC 7547, 7549, 7550 | Spiral galaxies with elliptical companions on arms | 2024-10-27 20:50:00 | This is a fascinating cluster which appears to capture 3 galaxies in a dance of attraction. The elliptical galaxy NGC 7550 on the top, center (south) appears to be dominating. It seems to have unwound the spiral galaxy NGC 7549 (bottom center) into an extended S curve, and to be attracting and stretching the more intact spiral galaxy NGC 7547 (probably a circular spiral at first). That said, I inverted the image to see if I could see any dust lanes indicating exchange of mass. Pushing on stretching the inverted image as hard as I dared (see gallery), I believe there's a hint of a connection between 7547 and 7550, and likely none with 7549.. I also wonder whether NGC 7553 participates in this dance as well (and possibly 7558). They're not included in the Atlas, but I wondered if they might have been outside the FOV of the Hale Telescope, and therefore not considered. So I investigated. According to the CalTech website, image scale at 1x (lowest) magnification on the Hale Telescope was 11.1" per mm. Plates were usually 5 inches x 7 inches, converting to 178 mm, or 0.55°/33". Turns out that the angular distance from NGC 7547 (western most) to NGC 7558 (easternmost) is under 10", so the FOV was not a limiting factor. |
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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 color capture and more in my grayscale, inverted image as well as 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 intended). 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 105 / NGC 3561 / Ambartsumians Knot | Elliptical galaxies connected to spiral galaxies | 2025-03-18 22:20:00 | This is a fabulous pair of interacting galaxies. Ambartsumian's Knot is the little dot right at the top ot the comparison images that is though to be the remnant of the extensive tidal tail pulled out of one of the galaxies. First observation of the night using the new 2500mc in Bin2. |
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Arp 112 / NGC 7805, 7806 and KUG 2359+311 | Elliptical galaxies repelling spiral arms | 2024-10-28 23:19:00 | A compact cluster of 3 galaxies, clearly interacting. The elliptical galaxy is NGC 7805, the largest spiral, is NGC 7806, and the small spiral in profile is KUG 2359+311. The two NGC galaxies are reasonably bright... the KUG has very low surface brightness which I can see nearly complete if I overstretch it and blow out the rest of the image. It is apparently a very strong UV emitter as it shows up on the KUG catalog, which is reserved for strong UV sources. It's unclear to me why the lower arm of NGC 7806 is so elongated. Arp categorizes it as "elliptical galaxies repelling spiral arms". Really? Seems to me that gravity attracts not repels. Remarks are blank for Arp 112, so no clues there. An alternative explanation might be that one of the other galaxies passed below from right to left before being captured and pulled back into the current orientation. The extended arm, therefore, might be a legacy of the "fly by". In any event, the two larger galaxies are close to each other and clearly exchanging matter. The KUG may be interacting with the spiral, judging from my inverted capture. |
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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. Indeed, after I concluded the last sentence, I checked Arp's remarks for 114: "Spiral somewhat pec., may be perturbed. See No. 25. " Peculiar indeed. |