Shakhbazian galaxy groups

[Martin Meredith]

Pre-dating and less well-known than the Hickson compact groups of galaxies is the catalogue of 377 potential groupings compiled by R.K. Shakhbazian in the 1970s. Like the Hicksons they were chosen amongst other things for their compactness, but are generally more challenging for visual/CCD observation, with a magnitude range of 14-19. Yet some (and perhaps many) are accessible to relatively small scopes with sensitive cameras in the short exposures that characterise this forum. 

Over the weekend I took advantage of the lack of moon and clear skies (SQM 20.2 = NELM 5.9) and relatively dry atmosphere (68% humidity, low for here) to try to track down some of the Shakhbazian groups with the 8" F4 Quattro and Lodestar-C.

On Friday I managed to catch two in the Northern skies. Both take the form of a long chain of galaxies, so while faint, are to my eyes beautiful gravitationally-bound galactic asterisms.

First, SHK 166 in UMi, found by star-hopping from the nearest object in the Skywatcher AZ-EQ6 GOTO database (SAO 2793). This was around 44 deg above the horizon. The wavy line contains 11 galaxies ranging in magnitude from around 14.9 to 17.8. A single 30s sub is shown below, together with an inverted, rotated and zoomed version (left) and the equivalent region from the DSS (right), the latter taken from http://www.andreas-domenico.de/astro/shkh_3.html (which reports visual observations with an 18" scope for some of the groups). This group seems to be about 0.5 billion LY distant.

Second, SHK 16 in Draco, star-hopped from SAO30112 at 33 deg, in a summed stack of 4 x 30s. This has 15 members listed in the catalogue but I could find magnitudes only for the first 7 (15.3-17.0). Together with the bright star these to me form a question mark. This group is a little closer, at 400 M LY.

On Saturday between the clouds and gusts of wind I went in search of further Shakhbazians in Pisces (which is home to 20 such groups). Here's SHK 40 near the border with Andromeda. No fewer than 60 members are listed; quite a few are visible in the centre of this single 30s shot (inverted). I have as yet been unable to find any information on magnitudes, but as mentioned in Domenico's document this cluster is the central part of Abell 193 whose tenth brightest galaxy is mag 16. This is estimated to be at two-thirds of a billion LYs.

Next, I attempted (and failed) to locate SHK 338 based on data in an article by Stoll and colleagues which suggests that this is a compact group of 7 galaxies in the mag. range 14.4 to 17.7, not far from PGC 216. I'm sure it is in the shot I took but my pattern-matching skills have not yet managed to find it.

Finally, I did manage to track down SHK 340 as a result of a long starhop from NGC 251. This is a 4x30s sum stack with SHK 340 just to the right of centre. The labelled inset is from Stoll et al (1997). Five components (1-5) are quite bright (15.4-16.2) and easily visible making up a horseshoe. Components 11 (17.7) and 13 (17.8) are just detectable, while 12, listed at mag 16.7, is not. (The missing numbered components have since been classified as stars).

Just above SHK 340 is SHK 340A (originally classified by Shakhbazian as part of the 340 group but now considered separate). Components 1,2,3 and 5 are clear (mags 16.9-17.8) and component 8 at mag 18.1 is just detected. (4 and 6 are considered to be stars).

These couple of nights were the closest I've got to visual-style observing with the CCD: extended star-hops to locate the field, lots of time spent poring over maps and documents, straining to make out every last identification -- and all for the sake of some faint fuzzies .  In other words, a huge amount of fun! 

Thanks for reading

Martin

[HiloDon]

Hi Martin,

Really great presentation and captures! You were the one who got me interested in the Hicksons and now I'll have to take a look at some Shakhbazians. You're getting some great results with that new 8". Amazing what the Lodestar can do.

Don

[arkosg]

Martin,

Nicely done!  I find it so impressive what short exposures with these cameras are able to capture - 

and the chains of galaxies are both graceful and aesthetic, to boot!  

Cheers,

Greg A

[Martin Meredith]

Thanks Don and Greg.

Don: I'm willing to bet you can see most of the Shakhbazians with your M-2 Lodestar and skies! The real difficulty at present is getting reliable positional information for some of the groups, but Aladin helps. I just checked there for the Shk338 field and it is just outside my capture region, so it turns out I spent a good 30 mins searching in vain (again, a bit like visual   ). Good for the brain though.

Greg, I know, I'm very happy to (just about) get down to mag 18 in 4x30s. Wait until I flock the scope and particularly the light shield. I'm temporarily using a green camping mat and I discovered that it is a great reflector of light pollution...

Martin

[nytecam]

Fantastic work Martin - you're really digging deep - way to go and really explore the universe

[Martin Meredith]

Fantastic work Martin - you're really digging deep - way to go and really explore the universe

Thanks Nytecam! And the deeper you dig the more there is to explore.