Arp’s Peculiar Galaxies
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Arp observations 1-10 of 89 total to date.
| Thumbnail | Title/link | Arp Category | Date Observed | Observer Description |
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Arp 1 / NGC 2857 | Spiral galaxies of low surface brightness | 2024-03-01 18:20:45 | Captured in an observation with Arp 285 in the same frame. Arp 285 was substantially brighter, but Arp 1 emerged eventually. No moon. A faint spiral galaxy with extended arms. Lovely once you could see it clearly! Significantly, the slightly extended upper arm of Arp 1 points at the two Arp 285 galaxies (see full image in the gallery), suggesting it may have been caused by a gravitational interaction with them. |
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Arp 6 | Bear Paw Galaxy | Spiral galaxies of low surface brightness | 2024-03-12 11:35:58 | What a "peculiar" target: tiny, moderate brightness! It appears to be 3 tiny dwarf galaxies merging, or else one or two tightly folded on themselves. I don't quite understand why Arp considered the peculiar aspect here to be the low surface brightness. For example, I've observed Coddington's Nebula, IC 2574, in the M81 Group, and it has much lower surface brightness besides being much larger and presumably much closer. Arp 6 seems much brighter. It seems to me that the three segments represent the more peculiar aspect.... |
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Arp 9 / NGC 2523 | Spiral galaxies with split arms | 2024-02-02 19:30:00 | This was a difficult night because of clouds. I set the brightness filters on SharpCap, but I was only able to capture 24 minutes in an over an hour, after which observing became impossible. While I would have preferred to spend more time on this target, the bar through the galactic center was very obvious, and the elongated, split arms on both ends were faintly visible. These were somewhat enhanced in Affinity Photo. |
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Arp 12 / NGC 2608 | Spiral galaxies with split arms | 2024-04-22 23:32:00 | This is a barred spiral galaxy with arms split up towards the east. Magnitude 13 capture was challenging on a full moon night. No obvious object that might have split the arms via gravitational attraction. A local star and the galaxy center appear as an "optical double"... I believe the galaxy center is the above (east) of the star. |
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Arp 13 / NGC 7448 | Spiral galaxies with detached segments | 2024-10-24 20:57:00 | Arp categorized this as "Spiral Galaxies with detached segments". Presumably this refers to the small, light ellipsoids in what you'd normally expect would be the darker envelope of the galactic disk. |
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Arp 16 / M66 / NGC 3627 | Spiral galaxies with detached segments | 2024-03-25 23:03:40 | This was a lovely, challenging object on a Full Moon evening. Obviously, the broad outline of the target was instantly visible in SharpCap, but the surface brightness was lower than expected. I presume Arp's category refers to the fact that the upper arm of the galaxy is pulled away from the disk of the galaxy (compared to a more symmetrical spiral). You could image that the arm was pulled away by an encounter with another galaxy at some point. Also indicating some sort of disturbance, the plane of the galactic center and nearby core is angled-in slightly towards the back of the disk compared to the plane of the outer arms. |
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Arp 18 / NGC 4088 | Spiral galaxies with detached segments | 2024-04-16 22:33:00 | Arp categorizes this as a Spiral Galaxy with detached segments, which is apt if not particularly evocative. Clearly the center of the galaxy exhibits a distinct spiral structure. I appreciate that Arp himself rejected the idea that peculiar galaxies were the result of mergers, but this certainly looks like a candidate for one. The segments above the spiral could be a second galaxy, partially merged, which we are viewing edge-on. It's gull wing shape could be the the center of the original, separate, galaxtic plane being attracted more quickly than the periphery. If the merger approached from the lower right and then swung around counter clockwise to its current position, it could help explain the lower detached arm. |
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Arp 25 / NGC 2276 | Spiral galaxies with one heavy arm | 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 of the "one heavy arm" in Arp 25 that is stretched in the direction of Arp 114. |
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Arp 26 / M101 / Pinwheel Galaxy | Spiral galaxies with one heavy arm | 2023-09-05 09:32:00 | This was one of the early observations after I took delivery of my EdgeHD 8", anxious to capture a closeup of M101 before the supernova faded. I started as early as possible on September 5, approximately 9 PM and captured 36 minutes, which is about the most I could as elevation was about to fall below my horizon. The big arm is evident although this pre-dated my interest in the Arp Peculiar Galaxies and was not a particular priority. |
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Arp 27 / NGC 3631 | Spiral galaxies with one heavy arm | 2024-04-22 00:57:00 | This was a very challenging observation due to a 93% moon and high clouds; it took over an hour to capture 26m of data due to SharpCap's brightness filtering. In the event, I was very pleased with the quality of the capture. This is a charming spiral galaxy, largely symmetrical, with the one lower arm extended. With its compact diameter and apparently dense disc, it resembles a miniature Fireworks Galaxy. |