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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). 

2074016303_Arp18915Apr21_16_30_58.jpg.0e494e42b3b524bd1a492a80dc3b9157.jpg

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)

761005093_Arp18916Apr21_09_02_26.png.a5c5d4c34352a4cfcf3ef861e9429ee1.png

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.

107516_Arp18917Apr21_06_31_34.png.d6e3b9bd0b17730eeacf486785a05233.png

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...

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

 

71127926_Arp7201Jun21_12_15_32.png.2d5b86c1a16890232aca578ad45c7488.png

Mike

 

Edited by Mike JW
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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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  • 1 month later...

Arp 99 in Pegasus is always a favourite to view for a few minutes. Arp classed it as a spiral with an eliptical on its arm NGC  7549, at the top with its arm extending to the elliptical NGC 7550 but he also included the NGC 7547 (spiral), on the right. The group are about 200 million lyrs away. This group are also Hickson 93 (component E is just out of shot to the left) and WBL 700.

NGC 7549 with the extended arms is classed as SBcd, NGC 7547 (Hick 93C) is also a ring galaxy (R)SAB, pec which is hinted at in  my slightly zoomed in shot.

Mike

 

1315872323_Arp9905Aug21_06_47_51.png.5210c45724885a6ce083c687c0c1e207.png1997540757_Arp9905Aug21_10_24_15.png.2552388f966d0c1543c723b02ba52132.png

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Glad you reminded us of the Hickson 93 designation as I couldn't find it under my Arp collection... What I find fascinating about NGC 7549 is the appearance of a sudden drop in intensity along the upper arm as if there's a discontinuity of some kind. I also recall thinking when I looked that the lower arm looked somewhat 'frayed' but I suspect these are artefacts. Here's a close-up from last year (which doesn't add much if anything to your shot, where your better resolution shows up in the various 'knots' along the bright arm)

 

1753058006_Screenshot2021-08-09at10_54_00.png.75a939e55fd25c1d25ec7838749ca3dc.png

Martin

 

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Hi Martin,

Really interesting to read your observations/thoughts. Here is a close up from my shot. It confirms the sudden drop off in luminosity of the northern arm. The lower arm is somewhat wider, fainter and appears not to extend as far as the upper arm.

Mike

1829287576_Arp9909Aug21_18_10_09.png.cbf07dca548becf86d9dbc8f5806cc10.png

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  • 1 month later...

Arp 150 also known as Hickson 95 lies in Pegasus.  The brightest galaxy is NGC 7609 (an elliptical). Arp put the galaxy in the "with jets" classification. The jet(s) would appear to come from the  companion. This is not the first time I have visited this group but it certainly my best shot as it clearly shows the straight tidal stream between the two galaxies and a separate curving stream (or is it - could simply be  curving spiral arm). Below the companion is yet more tidal stream - quite wide rather than narrow. I read one article suggesting there are 4 tidal streams which are shown in quality images. The companion is the galaxy that is being the most disrupted suggesting it has much less mass than NGC 7609.  Also in high resolution images the companion clearly has two bright nuclei. As always the question to ask, is are the four galaxies a true group? - only the right hand three are near to each other and may well in time merge. They lie somewhere between 539 and 564 million lyrs away. The galaxy to the left is 376 million lyrs away and intrigues me - does it have two nuclei (implies a merger) or is that a star superimposed to the right of the nucleus. Decent images would suggest it is a star.

 

2057839822_Arp15009Sep21_07_50_07.png.119ca271f664c524c34bb3d786440a78.png

 

Mike

Edited by Mike JW
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  • 3 weeks later...

I don't think we've had Arp 15 yet. This emission-line galaxy (NGC 7393) lies in Aquarius and is also known as VV 68. It has an unusual appearance rather like the head of an owl seen at an angle. Arp classifies it as a "spiral with detached segments".

The type is Scp D, something I've not come across before. Schroder & Kepler (1991) describe it as SB(rs) cP. I guess the p is 'peculiar'. More alphabetic soup to figure out!

362454630_Arp1506Oct21_14_26_16.jpg.47fbaee48a94df515b8e75af010302cf.jpg

Edited by Martin Meredith
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Hi Martin,

I am glad you are visiting these lower DEC objects as they tend to be in the murk for me. Re the classification, also given SB(rs)c pec H11 = barred spiral with arms that are not tight, no ring (rs) but possible transition to a ring structure, peculiar (as your shot shows - big tidal patch off to the right, and the owl eyes are they dust or patches of few stars), H11 plenty of action on the star formation. Your shot is very close to the standard images. I will try and visit this one if I can.

Mike

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Last night I gave Arp 15 a go and delighted with the result.  Arp classified this as galaxy with detached segments. I am not sure what he means by detached segments but in the ring you can see four 'lumpy' bits (massive star forming regions) which could be what he was referring to. The ring (almost a ring) and the large, wide tidal tail suggests an interaction with another galaxy but where is it?

 

846344254_Arp1507Oct21_14_42_38.png.5822de32a80d8880ebfef1b10719215c.png

Mike

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That is an excellent image, showing much better detail than mine. I wonder how much of that is down to resolution, seeing or tracking differences.

The closest galaxy I can see if NGC 4716, about a degree away but at 134 MLys compared to 178 MLys for Arp 15. 

This paper lists NGC 7393 as not having a companion: http://articles.adsabs.harvard.edu/pdf/1985ApJS...57..643D

Martin

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and here are some more Arps from Aquarius.

Arp 3 is a low surface brightness galaxy (which is how Arp classified it), about 60 million lyrs away.

483285267_Arp307Oct21_08_05_28.png.1433bfe47cdf73f5e820a8bf80349f36.png

Arp 314 was classed in groups of galaxies by Dr Arp and lies about 150 million lyrs away. It would appear that Arp included all four galaxies. All four appear to be interacting with a long tail going off to the SE to the dwarf galaxy (no redshift available) - just got a hint of this tidal stream as well a tidal stream between the two bright galaxies

1956878572_Arp31408Oct21_13_42_19.png.37db833f68c61fc767aa0624d8fc57fe.png

Mike

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I don't think I've observed Arp 314 but it looks really interesting, especially with that strange detached arm (?) to the S. The Arp Atlas notes how extremely faint some of the structures are. You did well to pick up a hint of the SE tail.  I'll see if I can make it out tonight, assuming transparency is better than last night...

Meanwhile, here's Arp 3 from this time last year. Like all low SB galaxies it is somewhat frustrating with its amorphous and ill-defined shape, but there are some interesting features. The photo in the Arp catalogue has much more structure.

1346672990_Arp308Oct21_15_00_37.png.a4a41f26d1edfee7983109f9aee3ec61.png

Martin

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