Compact groups in the Updated Zwicky Catalogue

[Martin Meredith]

I came across a group of 4 rather bright UGC galaxies in Delphinus the other night (more on this in the next post) and wondered if they had a group designation. They are rather typical of many WBL galaxy groups but after some checking I found that this particular group is not a member of the WBL catalogue. Typing the UGC id of one of the galaxies into Simbad suggested that it was indeed a 'galaxy in group of galaxies', so the hunt was on for the relevant group catalogue.

Some further searching turned up an article from 2002 entitled Compact groups in the UZC galaxy sample by Focardi and Kelm [1], the UZC being the Updated Zwicky Catalogue of galaxies [2], and the group I'd seen is the 269th member of that catalogue. I'm not aware of an official name so I'll refer to it as the Focardi-Kelm catalogue, or UZC-FK for short.

The UZC-FK was prepared using an automatic neighbour search algorithm operating in 3D i.e. incorporating both apparent position and distance data, since the UZC contains redshifts for nearly 20k northern galaxies. The main criterion was proximity in 3D. More details can be found in [1].

The Focardi-Kelm catalogue contains 291 compact groups, of which 30 are Hicksons. Group sizes range from triplets to 9-strong groupings; in fact, the majority are triplets. The lowest declination is a mere -3 degrees, so the entire catalogue is visible for northern observers apart from anyone observing at or near the North Pole. I imagine there is some overlap between this catalogue and WBL. The galaxies are quite bright, ranging from 11.3 to 15.5. I'm quite excited to come across a new (to me, at least) catalogue and the range of magnitudes suggests that this will be ideal for EEVA since the galaxies are bright enough for a fair amount of structure to be visible (unlike the Shakhbazian or Palomar compact group lists).

I've prepared a data file of the entire UZC-FK compact group catalogue below so if anyone fancies adding observations to this thread, please do so. I have absolutely no idea what most of the groupings look like but am keen to find out!

uzc_fk_compact.csv

Martin

[1] http://simbad.u-strasbg.fr/simbad/sim-ref?bibcode=2002A%26A...391...35F

[2] http://simbad.u-strasbg.fr/simbad/sim-ref?bibcode=1999PASP..111..438F

Edited October 11, 2021 by Martin Meredith

[Martin Meredith]

This is the 269th member of the catalogue I'm calling UZC-FK and immediately we have a bit of an issue. The catalogue identifies the 3 uppermost UGCs as part of the same group.  

 

The galaxies have redshifts corresponding to distances of 198-232 MLyrs. The leftmost, UGC 11572, is a mag 14.9 elliptical. To the south of that is mag 15.3 UGC 11571, type Sc(bar). Across on the right is mag 14.9 UGC 11568, also type Sc. The beauty of this field for me comes from the density of stars in which these galaxies seem to float.

What about the 'obvious' 4th member, UGC 11569, a mag 16.0 Sc that forms a nice triple with the galaxies to its NE? This seems to me to be a clear member of the group, since its stated distance of 220 MLyrs is bang in the middle of the group estimate. The reason it isn't part of the group in the catalogue is presumably because of a strict mag 15.5 cutoff that was applied (due to the Updated Zwicky Catalogue having this limit).

With this catalogue, one has to bear in mind that the groups were chosen using an automated approach based on clearly stated criteria. This has the advantage of eliminating human bias, but the disadvantage of producing groupings that may not be complete. 

For me as an EEVA observer, the main benefit such a catalogue is to point me in the direction of objects that I might otherwise not look at!

Martin
  

[Martin Meredith]

During Monday night I had the opportunity to observe a reasonable sample of UZC-FK groups in DEL, AQR, PEG, PSC and AND (16 in all). Here's a selection of the more interesting groups. My impression is that the word 'compact' is used quite loosely since many of the groups are quite widely spaced (although all the ones I looked at fit into a 0.44 x 0.34 degree FOV). Most of the HIcksons are more compact, and certainly the Palomar and Shakhbazian compact groups are much more compact, at least based on the UZC sample I made.

I'm still not 100% sure of the actual members that the algorithm associated with each group, so what I've labelled are my best guesses.

UZC-FK 281 is one of the more numerous groupings, containing 6 NGC galaxies. NGC 7389 is an interesting case, type SBa(bar). Zoomed in (not shown) it looks like a miniature Saturn (the bar + inner ing?) embedded a large diffuse elliptical halo at a right angle to the 'Saturn' rings. Just to its left is a mag 19.3 z=3.3 quasar.

 

USC-FK 287, also in Pegasus, is a more typical 'triplet' group consisting of somewhat fainter galaxies. As you can see, this is far from compact. What I like about this field is the way two of the galaxies appear to be hiding in the lee of stars. The upper UGC galaxy has a type I don't see very much: IB(bar, diffuse) i.e. irregular but with a bar.

 

UZC-FK 271 is another triplet, this time in Delphinus. The star here is NGC 6956, type Sb(bar, ring) with its asymmetric profusion of arms, star-forming regions and background halo.  UGC 11623 is type Sa(bar, ring) with a classic 'steering wheel' shape. The eagle-eyed will spot that this is dated 8th Oct. In fact, I observed this field on the 8th before I'd heard of the UZC-FK catalogue, so I've renamed the shot (I re-observed it on Monday without realising).

 

Perhaps the highlight for me is UZC-FK 280 in Pegasus. I haven't added labels here to avoid detracting from the lower group. Actually, it is hard to decide which are the 6 galaxies in the group as there are more than 6 with a distance spread of 360-450 MLyrs and magnitudes under 15.5. The perfect (90 deg) edge on  at the top left is NGC 7345. The group of 4 bright and 3 fainter galaxies at the base of the image deserves to be better known. It is the equal of many Hickson groupings. This group can be found not far north of Stephan's Quintet on a line that also include the marvelloous NGC 7331, so it might be that casual viewing are taken up with those delights.

 

Finally (from this selection), here is UZC-FK 272 in Aquarius. This is another group of 6 NGCs. I reoriented the field a little to improve automatic label placement, so N is no longer up. I have a strong feeling that I've seen this field before. NGC 6962 calls out for all the attention, with its exotic SABa(bar,ring,mult) classification. Along with its elliptical neighbour NGC 6964 it is also a member of the overlapping galaxy catalogue. NGC 6959 at the top is another Saturn lookalike, actually a S0(bar, ring). There are plenty of foreground stars that might have been supernovae -- I check on Aladin during the observation. It struck me that observing a bunch of galaxy groups of an evening is a good way of maximising chances of finding a supernova!

 

 

Of course, these are some of the highlights of the session. There are also as many cases of relatively faint triplets. The fun is typing in the coordinates and wondering what will turn up.

Thanks for looking

Martin

 

 

[Mike JW]

Hi Martin, Plenty to view and enjoy in your posts. The UZC catalogue looks very promising.

Delphinus  - UZC-FK 269. My shot adds little to yours except for UGC 11568 which intrigued me. Close up is shown below. Obvious asymmetrical dust lane, hints of lumpiness. The galaxy extends quite some length to the north (just picking it up) and the opposite side it starts to curve. Classification seems uncertain Scd?

Delphinus UZC-FK 271 - plenty going on with this one. UGC  11623 so clearly a ring galaxy as you indicate. NGC  6956 - what a beauty. Two obvious arms off the bar but is there a third arm coming off to the right and tight to the nucleus. Also the main arm going off to the right does it split? or just an illusion.

For the sake of completeness here is the third UZC in Delphinus , UZC-FK 273. not much to say about it!!

 

[Martin Meredith]

Thanks for including your captures Mike. I also looked at 273 and my notes say "this one not so impressive and not so compact!", so it looks like we're in agreement.

Others I observed:

2, in Pisces. Triple, but 4 galaxies in field, one of which is more distant. 2 NGCs (7825, 7827) and 2 UGCs (33, 37). 

5, in Andromeda. This is a 7-strong group that includes NGCs 79, 80, 85, 85b, 86, 90, 93, the latter 2 forming Arp 65. Very impressive group but I haven't included it as we've seen this before in the Arps section

7, in Pisces. This involves NGC 125, NGC 126 and IC 17 but claims to have 5 members, so they must be outside my FOV

270, in Aquarius. Triple of 3 similarly-oriented edge-on spirals in a moderately-dense star field

274, in Aquarius. Triple, including IC 5090, quite an impressive Sa spiral, all at around 450 MLyrs

282, in Pegasus. Quadruple. Seen this before! VV 84. Impressive. Actually compact!

283, in Pegasus. Triple, though 4 in field. Three < mag < 15.5; 4th at a similar distance.

285, in Pisces. Triple. Equilateral triangle of edge-on galaxies in field but one is much closer (though same apparent size), so identity of 3rd is a mystery.

286, in Peg. Triple. Compelling grouping of 3 rather similar UGCs at around 290 MLys. So compelling I'm compelled to add a picture! Top to bottom: types Sc, Sbc, SBc(bar). Presumably interacting. This is RSCG 85 (see below).

289, in Pisces. Quintuple although I only found 4 galaxies meeting the magntiude criterion in the field, including NGC 7704, 7705 and 7706. 

 

 

As well as being cross-referenced to the Hicksons, the groups are also cross-referenced to the Redshift Survey Compact Groups (1996, 1998). I think these might need their own thread!

Martin

 

 

[Mike JW]

A very good haul of the UZCs.

I too took a look at the 280 group - beautiful group. The edge on galaxy at the top caught my eye. - NGC 7345. Below is the close up and using a log stretch. It appears to have a double nucleus ? NED data does not show an object for this second nucleus - interesting.

UZC-FK 281 - NGC 7389  - Martin you mention a close up - see mine below. I agree with you that the Saturn effect is likely to be a ring galaxy seen from an angle.

You mentioned Stephan's Quintet in the thread = UZC-FK 279 - so here it is from the other night - probably my best attempt ever.

Mike

 

 

 

[Martin Meredith]

Fascinating to see the double structure of NGC 7345 in group 280. I missed this first time round. If you choose the SDSS9 layer in Aladin the second region is visible as a very blue source. What's also evident from that image is that this may be a box-galaxy with the characteristic X-shaped structure crossing the core.

I checked online and there is a recent paper on ultraluminous x-ray sources [1] whose Fig. 14 shows this galaxy, and suggests that just to the side of the lower structure there might be an intermediate mass black hole candidate...

Re Stephan's Quintet, you can see from my avatar that I recently looked at this again too!

Martin

[1] https://arxiv.org/pdf/1812.04684.pdf

 

 

[Mike JW]

Hi Martin, I took a look at the SDSS9 and the blue dot is clearly a star in our galaxy. The article is technical but I get the gist of it and the images showing the likely places for IMBH candidates is good.

Mike