Arp’s Peculiar Galaxies
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Arp observations 151-155 of 155 total to date.
| Thumbnail | Title/link | Arp Category | Date Observed | Observer Description |
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Arp 327 / NGC 1875 / Hickson 34 | Chains of galaxies | 2025-01-02 20:41:00 | This is a tiny, dim group consisting of four galaxies: the brightest is an elliptical galaxy, NGC1875 (13.7m, 0.8'x0.7'). Then, moving up the chain (and the image): PGC1716 (18.3m, 0.2'x0.2'), PGC17175 (17.1m, 0.4'x0.2'), and PGC17173 (17.4m, 0.4x0.2m). The smaller, dimmer galaxies appear to be younger and spiral. Consistent with the close proximity of the four, filaments connecting them are evident. Arp's comment: "Three distorted galaxies in general line toward east." I agree. One imagines that the ultimate outcome will be that all 3 end up absorbed into NGC1875. Imaged on a windy night that required careful use of SharpCap's brightness and FWHM filtering. I was hoping to capture up to an hour of integration, but clouds closed out observing prematurely. |
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Arp 331 / NGC 383 | Chains of galaxies | 2023-12-06 22:00:06 | This is a very rich galaxy-field. Why Arp included it is a little unclear; his remarks are typically cryptic: "Position of NGC 383. Symmetry around large central galaxy. Velocities known." Besides the galaxy cluster that Arp labels, I counted 12 additional galaxies by eye. The Astrometry.net annotation is so cluttered that it's very challenging to read. Included as part of Arp 331 are NGC 383 (central galaxy), 379, 380, 382, 384, 385, 386, and 388. Additional galaxies within the field of view include: NGC 370, 373, 374, 375, 392, 397, 398, 399, 400, 402, 403 plus IC 1614, 1618, 1619. This means the annotation found at least 2 galaxies I didn't count by eye, presumably the IC galaxies (IC 1614 is 17th magnitude). This observation was part of the December 2023 Cloudy Nights EAA Challenge, which is why I observed it when I did. |
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Arp 333 / NGC 1024 | Miscellaneous galaxies | 2024-12-25 23:23:00 | This is an enigmatic cluster of 3 galaxies, showcased by NGC 1024, although Arp included only NGC 1024 in his Atlas. It's classified as miscellaneous/unique for unknown reasons. His remarks state: "Thin circular arms, star in SE superposed on wisp." I wasn't sure that those objects might not be dwarf galaxies, especially because of the superposition, but it turns out that all of the bright shapes with the comparison image are blown-out field stars. NGC 1029 is likely gravitationally bound to 1024, but 1028 is substantially further away as suggested by its smaller size, and confirmed by a much higher red-shift. But, strictly speaking neither is part of Arp 333. |
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Arp 336 / Helix Galaxy | Miscellaneous galaxies | 2025-03-21 21:49:00 | Arp 336, also know as NGC 2685 and as the Helix Galaxy, is a lenticular polar ring Seyfert Type 2 galaxy in the constellation Ursa Major. Polar-ring galaxies are very rare: it refers to a ring surrounding the galaxy orthogonal to the disc.. They are thought to form when two galaxies gravitationally interact with each other. "The bizarre configuration could be caused by the chance capture of material from one galaxy by a second disk galaxy, with the captured debris strung out in a rotating ring. A Seyfert galaxy is a type of active galaxy characterized by a bright, compact nucleus exhibiting a very hot, energetic region at the center, thought to be powered by a supermassive black hole. <--> There are two observations here: one early in my EAA career (Dec 2022) and the second in March of 2025 (featured). I was about 110 Arp observations into my experience curve in March of '25, and it shows. You see both in the gallery.. March of '25 I was using my 8" EdgeHD with a monochrome camera...this is a rig I'd adopted specifically to capture dim galaxies. December of '22, I'd had less than 30 days of successful captures. Arp was not even a twinkle in my eye. This is a relatively small target which tested the limit of my reduced C9.25 SCT, particularly because I had no idea what I was doing at the time. |
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Arp 337 / Cigar Galaxy / M82 | Miscellaneous galaxies | 2024-02-19 20:23:00 | Recorded February 9, 1781: "Nebula without star, near the preceding [M81]; both are appearing in the same field of the telescope, this one is less distinct than the preceding; its light faint & [it is] elongated: at its extremity is a telescopic star. Seen at Berlin, by M. Bode, on December 31, 1774, & by M. Méchain in the month August 1779." Halton Arp included M82 as one of 11 Messier "Peculiar Galaxies" in the "Miscellaneous" category, and commented "Internal explosion" <--> The broad outlines of this disrupted spiral galaxy are immediately obvious, but the details of the galactic center -- Arp's 'internal explosion' -- emerge much more slowly. Our view is nearly edge-on, and the spiral disk bends slightly near the the center towards the left. The base of the disrupted/exploded core is readily visible. Its furthest boundary is less clear. At star parties, when I explain my personal fascination with "Peculiar Galaxies", I usually offer this as the live EAA example. As with all of my Arp observations, the first image in the gallery is a comparison of my capture to the image Arp provided in his Atlas. Most were imaged using the 200" Hale Telescope on Mt. Palomar, on 5"x7" photographic plates. I created an inverted monochrome version of my capture that follows the comparison shot which shows the disruption a little more clearly, though less than Arp's does. |