Shakhbazian 10: a very rich compact galaxy group in Bootes

[Martin Meredith]

SHK 10 is the second most galaxy-rich of the 377 Shakhbazian compact groups (*), packing an astonishing 32 galaxies into a space of little over 6 minutes of declination. On the other hand it is rather faint: its brightest member shines at mag 17.7 from a distance of around 1.7 billion light years. SHK 10 can be found centred at [14 10' 56.1"  +46 15' 54.7"] a degree or so from mag 4.2 lambda Bootis heading towards the border with Canes Venatici (chart BOO/5769 in the Pretty Deep Maps collection). Here's a screenshot showing the locations of the galaxies, numbered using Shakhbazian's scheme.

For me, the challenge of the Shakhbazian groups is seeing how many members can be pulled out using near live viewing techniques -- literally seeing more and more of them appear on the screen as live stacking does its magic. To give a flavour of the live experience, I've prepared a cropped animated gif showing the progress as more subs come in: 1, 2, 4, 8, 16, 32 and 64 in total. This was also a test of fast stacking so the subs themselves are short, at 10s. Note that this is all live stacked in LodestarLive v0.12 and not post-processed in any way apart from rotation to match the chart. I retained the same brightness and contrast settings throughout, and used the ^0.25 compression mode. The group is in the central third of the shot.

[Edit: animation appears not to work yet … here's a temporary dropbox link (0.5M)]

Noise is greatly reduced by stacking, revealing the galaxies.

Here's the last frame (64x10s stack) in full. Note the super-thin galaxy at top-right. This is mag 16.3 UGC 9066 at a distance of nearly 400 million LYs. 

Here I've blown up the central portion and labelled the constituents. 

There are a few obvious stars amongst this group and also some interlopers -- things that look like galaxies but are not listed by Shakhbazian. Checking the SDSS image using Aladin these are definitely galaxies. Whether all belong to the same physical cluster is another question. As recently as 2012 there were only 13 spectroscopically-confirmed members.

The ones I've failed to split are 19/20 and 8/24, though the latter actually appears to be a single edge-on galaxy in the SDSS image.

Details: SQM 20.2, windless, no moon, around 50 degrees up. Skywatcher Quattro 8" f/4, Lodestar mono X2, LodestarLive v0.12, no filters, AZ-EQ6 mount in alt-az mode. 

Cheers

Martin

(*) The title goes to SHK 40 in Pisces, a relatively-bright 60-member group also known as Abell 193. 

[Martin Meredith]

OK, this seems to work...

[stevewanstall]

Thank you for the really interesting pictures.  Mind boggling to think of the time. distance, number of stars...

[JamesF]

Fascinating.  And a particularly good illustration of the effects of stacking.  Love that edge-on galaxy you pointed out, too.

James

[Paul81]

Great capture Martin, and as always a great education as well as most of these groups I never knew existed.

The animated GIF is brilliant and really sums up the beauty of EAA.

I'm still amazed how well the live stacking has worked out... when I originally designed and wrote the algorithm and released it I was expecting a bow wave of issues   Normally complexity and trouble free operation don't go hand in hand! Maybe I got lucky?! Lol!

[Martin Meredith]

Thanks everyone.

Steve, its the mind boggling aspect that draws me in every time. These little specks are not much to look at individually but grouped and put into some kind of context and the mind does the rest...

Cheers James. I've loved thin galaxies ever since M82 swung into view with a big dob. 

Paul, the live stacking is a game-changer, as they say, and opens up EAA in many ways -- not just improving image quality but increasing the live feel and perhaps permitting EAA with low-budget mounts. As a fellow software person I appreciate how difficult it is to get complex algorithms working robustly and still maintain a simple user interface.

Martin

[Paul81]

Oh yes! I always keep occam's razor as my number 1 rule of engineering and has always paid off. Even complex things can be broken down into more simplistic forms, and so on and so until you arrive at lego bricks... Doesn't always work out, but more often that not pays dividends!