ACO 1185/Arp 105/Ambartsumian's Knot

[Martin Meredith]

A briefish unexpected session last night before clouds rolled in had me with a list of targets based partly on others' Arp observations in this forum (thanks!). I didn't get round to them all or even that many, and the one I'm posting here wasn't on the list, but I couldn't resist a look at what must rate as one of the most fascinating areas of the spring sky for lovers of peculiar galaxies and galaxies in general. This is Abell 1185 in Ursa Major, almost on the border with Leo and Leo Minor. The region contains countless galaxies including 5 NGCs. Most of the things in the capture below are galaxies. Here's a chart containing this cluster: LEO4928.pdf

I've marked VV 1419  (NGC 3550), a lenticular galaxy, presumably a member of the Vorontsov-Velyaminov catalogue of interacting galaxies due to what looks like a double core (or even triple, though there may be some foreground stars involved). I need to delve into the literature to find out more about this.

The other marked galaxy (group) is Arp 105. It isn't very obvious on this image, but there is a long plume rising vertically (N is up) from UGC 6224, the upper of the two galaxies making up Arp 105. This plume ends in a wider but more concentrated cloud.

LEO4928.pdf

 

 

The plume and other elements are better seen in the inverted image, zoomed in to show the structure more clearly. This structure is sometimes called the Guitar.

The thing I wanted to observe was Ambartsumian's Knot, which according to wikipedia is a dwarf galaxy resulting from the tidal tail of stars pulled out from one of these galaxies. https://en.wikipedia.org/wiki/NGC_3561 

There is also a mag 20.2 quasar just about detectable (I'd describe it as highly marginal though).

Incidentally, although this looks like terrible tracking errors/field rotation (and there is plenty of that), it is in part an illusion as many of the smaller galaxies around the periphery of the shot happen to have that kind of orientation! 

 

 

 

Thanks for looking

Martin 

[elpajare]

A great job, interesting and instructive.
In addition to a good technique to be able to photograph it

[London_David]

Thanks for pointing that one out - interesting forces and structure there.

I have been looking forward to going through the Arp catalog, there’s some really fascinating objects. I just got a book with the original plates and I’m really interested to see what I can get from my back garden with modern equipment versus what Arp could see from Mount Wilson.

Alas it’s been very cloudy over the past week and haven’t had a chance to do anything. Perhaps tomorrow...

[Martin Meredith]

Thanks elpajare and David. Is that the Arp book from Kanipe and Webb? If so, one of my favourite observing books. I wish there were more like this.

Martin

[Mike JW]

Hi Martin,

Cracking observation. Needless to say my shot from earlier this year lacks your detail but I did pick the three cores of W1419. I think I should probably re visit all my Arps and start again - fun stuff and fascinating. Thanks for the inspiration.

Mike

[Martin Meredith]

Thanks Mike. I managed to find an article on this cluster that mentions NGC 3550, describing it as a 'complex system of 3 smaller galaxies within a common envelope ... a merging system... a brightest cluster galaxy caught in the act of formation' so in reality there are 3 galaxies here merging. 

This is the article https://www.aanda.org/articles/aa/pdf/2011/04/aa15939-10.pdf which is actually about finding intergalactic globular clusters floating around in this galaxy cluster. Fascinating! I would love to be able to catch one of these but it looks to be some way beyond my current kit!

Here's a couple more from last night (neither of them Arps, but I do tend to latch on to something that looks interesting:

 

[London_David]

On 09/04/2019 at 10:47, Martin Meredith said:

Thanks elpajare and David. Is that the Arp book from Kanipe and Webb? If so, one of my favourite observing books. I wish there were more like this.

Yes -- it is. It is really good. If you like that the Annals of the Deep Sky books are really good too. Not just galaxies but a range of objects. The Cambridge Photographic Atlas of Galaxies is also a favourite - more pictures but plenty on the astrophysics too. 

I'll post images later -- but I tried Arp 105 last night and completely failed to even find the thing... I plate solved to get there so it should be in the image, but there's nothing there. I even got the maps out and struggled to place it manually. 

[Mike JW]

Hi, I was out there last night and determined to give Arp 105 another look and use more appropriate settings.

Pleased with result.  Not as clean or smooth but then I am not using darks etc.

The knot is there, the bright end to the tail has a name (see below) as does various other bits. Did not pick up the Quasar, although in the noise there is a bit of grey that might qualify?

I quite fancy another crack at this object.

Cheers

Mike

PS I also looked at 3993 and 3501 - may post them later.

[Martin Meredith]

Great work Mike. It is really hard in short exposures to get something even visible without inverting for that plume, and yours looks clearer with a more continuous plume than mine. And also in in the correct orientation for a right-hand guitar ?

Martin