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ARP GALAXIES


Mike JW
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Here's one I ended last night's Coma session with and it turned out to be quite a surprise. This is Arp 189, aka NGC 4651, a type SA(rs)bc ie a late-ish non-barred spiral with an inner ring. The details revealed are pretty interesting in themselves, with a kind of bright heart-shaped split ring on its side and much fainter outer arms.

1778285972_Arp18915Apr21_16_32_52.jpg.5bcd023689e53d32fe1ce771e51fe9d2.jpg

I was observing this for a few minutes before wondering what the peculiarity was. It took quite a while longer for me to notice an exceedingly faint and perfectly linear structure heading off to the East (left in this image). I continued observing for quite a while, hence the 10m length of the total exposure, to see if this was real or an artefact. Eventually it became 'clear' (to some extent!) that this was a real feature. Sure enough, reading about it now it comes under the class 'narrow filaments'. 

Forgive the overexposed core but this was the only way I could produce a visible image of the filament, which is most unusual, having as it appears to a near-90 degree left turn at the end of it. I have no idea how this came about (more reading later). 

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This is perhaps the most challenging Arp I've encountered to date.

cheers

Martin

 

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This article is worth reading for more on Arp 189/NGC 4651, apparently known as the Umbrella Galaxy (due to the extended halo around the galaxy and the 'bent stick' of the tidal stream -- remind me to reorient my image next time...). 

https://arxiv.org/pdf/1406.5511.pdf

Fig 1 provides a wonderful view of the tidal stream whle Fig 2 gives plenty of material for anyone interested in seeking out globular clusters and planetary nebulae in this galaxy. These relatively bright objects are being used as stream tracers.

Martin

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Martin's Arp 189 shot intrigued me at two levels; 1. actually getting hints of the extensive nature of this peculiar galaxy with just an 8" scope, 2. how does such a galaxy come about? This for me is the fun and pleasure of EEVA encompassed in  the 'observation'  of just one DSO.

When I first viewed Arp 189, I did not even think to try for the filament - before the days of Jocular. 

First up is my C11 and an ASI 174MM camera - too much noise and amp glow and just a hint of something but not really!

1525752910_Arp18917Apr21_06_36_13.png.4e6c12ac8302584f86c2fb9197d0bb1e.png

 

Next I swopped cameras and tried the Ultrastar with the C11 - whoops I forgot to orientate it the same. - better view, but nothing to write home about despite increasing the time. (annoying dust bunny as well)

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The following night under similar conditions I wheeled out the 15 and slotted in the ultrastar. Hey presto I have the filament going off to the left, the extensive diffuse faint star halo going off to the right and detail of this rather attractive spiral. Also there is a mag 20 quasar and various other faint DSOs.

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Thanks Martin for the challenge and inspiration for this fascinating galaxy.

Mike

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Its great that in the 15" + Ultrastar you can preserve detail in galaxy as well as seeing the tidal stream.

I was hoping to look at this again last night by combining L and OIII but the clouds rolled in shortly after setting up the scope (grrrrr).

I note from that article that the PNs and GCs that are being used as tracers for the stream are incredibly faint and probably beyond EEVA techniques short of investing in a very large aperture scope...

Martin

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Here are a couple of Arps from Leo.

Arp 5 a pair of galaxies that lie about 80 million lyrs away, Arp classified this as a low surface brightness spiral. It is also VV 251, designation PKdf = pair in contact with disrupted facade (messed up).  NED = SB(s)m pec, it is a small galaxy and severely disrupted by the merger process.

1450851091_Arp515Apr21_18_20_26.png.c5ce836fb47abe0b763358330e4ce470.png

 

Arp 87. This pair are 349 million lyrs away. Classified as SAB(rs)c; pec and is actually in the process of forming a polar ring. Arp classified this pair as spiral with large high surface brightness companion on arm. Also known as VV 300 and given the PD designation (distant pair).

926531658_Arp8715Apr21_18_21_43.png.dc69e8f1c7dfb7ef73f3d32ea931be29.png

Mike

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Arp 5 is 'well weird'. I looked at both of these last year but my images don't add anything new to yours -- my Arp 87 has less definition.

Here's one of my own from the other night that has something of a family resemblance to Arp 87. This is Arp 240 which consists of NGC 5257 (SABb) & 5258 (SBb) involved in a graceful exchange of gases. I've stretched this quite a bit to bring out the linking structures that are really quite faint for my setup.

328881739_Arp24020Apr21_21_43_45.jpg.e0cd450bae4fcd53aa005703e78079a6.jpg

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  • 1 month later...
Posted (edited)

Arp 72 in Serpens - NGC 5996/5994. Also known as VV016. I visited this Arp twice in 24 hours, trying to see just how much of the extensive faint arms I could pick up. As is often the case I get side tracked. Arp classified this pair as spiral galaxy with small high surface brightness companion on an arm. The two galaxies are separated by about 1 million lyrs and lie 157/156 million lyrs away. 5996 is classified SBc pec or SBc,WR,H11,Sbrst . The interaction between the two galaxies has certainly disrupted 5996, leading to much star formation (H11 regions) and intense star formation (Starburst). Spectral analysis shows the presence of Wolf Rayet stars (WR).

My upper shot is a longer exposure to get hints of the extensive/faint material on the NGC 5994 side (the small companion) and also hints of the sweeping arm to the north (up) which then curls left and down. The lower shot has two distant galaxies marked - both a mere 3.8 Gyr away!!!! I have not checked out the various fuzz spots for the presence of galaxies.

1985085078_Arp7202Jun21_17_00_44.png.23bc545dd5ef6f6da21c2b27a92a243f.png

 

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Mike

 

Edited by Mike JW
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Nice shot and write-up. I'm quite taken by the little cluster of stars to the SSW. Looks like a couple of optical doubles at least.

It is interesting to visit the same things on successive night just to see how much seeing affects the view.

Martin

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I'd forgotten that M82 is also Arp 337

It is categorised as 'unique' within the Arp catalogue and it is easy to see why.

I've also marked three quasars. These are known (from top to bottom) as Hoag 1-3 and have the distinction of having almost identical redshifts (as marked), leading to the controversy over whether such similar redshifts could have occurred within such a small grouping by chance. (Nowadays there are more than 2 million quasars catalogued so it isn't such a big deal, I guess).

Anyway, back to the observation. I think I've only managed to pick up Hoag 1 and possibly not even that, but I would hope others will have a go at detecting these three.

406261681_Messier8207Jun21_17_17_26.jpg.b5d62eaa9aecfc875ca57ebf1bbbb3ac.jpg

 

 

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I have checked my M82 shots from the past - no sign of Hoag 1-3. However I notice below the number 9 of 20.9 the faint fuzz you have picked up is probably a galaxy at 2.6 Gyr distance.

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