Palomar Compact Galaxy Groups

[Mike JW]

Palomar Compact Galaxy Groups are distant, faint and compact groups of galaxies and present a difficult observational challenge but using the EEVA technique makes it somewhat easier to view.

Resources:

Alvin Huey - http://www.faintfuzzies.com/Files/Palomar Compact Galaxy v1.pdf, is a useful resource.

Here is my list from VizieR Palomar Distant Compact Galaxies BIG LIST.xlsx

My list contains the hyperlinks to take you to relevant data pages.

Last night I attempted my first two Palomar Groups. It was a nightmare trying to be certain I was in the right area. One success and one failure.

Palomar 2259+1329. This turned out to be reasonably easy to find. I went to UGC 12281 first (what a beauty it is) - bottom left and from there I edged the scope toward where the target should be. This galaxy points to the 'suspects' - not highlighted in the shot - take a guess as to what bits of fuzz they might be.

 Below is a close up of the group and to the right is the image from the Alvin Huey publication.

See labelled image below for mag details

Here is some data from NED. A=about 586 million lyrs away. B = about 400 million lyrs away. Assuming I have understood the data correctly (I had to convert redshift values) then this group is not a true group? No data for C and D.  Galaxy -16.1 is about 400 million lyrs away. The area of extended fuzz has 5 data points in Aladin - galaxies, some with no data.

Finally just below the label '19' there is a triangle of noise? coincides with three galaxies one of which is mag 19.8!!!

Mike

Edited August 23, 2020 by Mike JW
more info.

[Martin Meredith]

Very interesting post, Mike. There is a whole world of compact groups out there that I imagine are barely observed yet fascinating to look at. There is something in particular that is appealing about chains of galaxies too.

You're right about that super-thin galaxy -- a wonderful object!

Part of the enjoyment with EEA with these faint objects for me at least is the process of star-hopping (and occasionally galaxy-hopping too), which is just as much fun as visually. That's partly why I'm resisting the (academic) temptation to incorporate some kind of plate solving in the tool. Where would be the fun in having the object of interest appear bang in the middle of the sensor every time! There's also the serendipity of coming across other interesting things en route.

Martin

[Mike JW]

Hi Martin, I agree re the challenge of finding a small target. It took me two sessions to find this one.

Mike

[Mike JW]

19/09/20.

Palomar PCG J1525+2956.  Found in CRB.

Poor conditions and low down so not easy to get a clean image.

Four members, about 1.5 billion lyrs away, mag 16-17. Other galaxies picked up as well

 

[Mike JW]

Nov 12, 2020. I managed to use the brief window and track down some more Palomar Galaxy groups.

First up, I revisited Palomar 2259+1329 (see start of this thread) and I was able to better separate out the mag 19.2 galaxy. I have also found out that it is about 1.9 billion lyrs away so not part of the actual group.

 

Next up is Palomar 010402+201746. A group of 4 members. This one mystified me because I could see a faint fuzz near a line of 3 stars, near the centre of the fov. This morning revealed that the stars are indeed galaxies (mag 16) and the fuzz is the fourth member (mag 17.7). So why do the galaxies look star like? - may be they are tight elliptical? - no information on the group re distance.

Palomar 233230 + 114431. No trouble spotting this group of four. The star like one is the brightest at mag 16.4, the other 3 are mag 17, with the fainter one of the three being 17.9. I find it tricky doing the ID for the individual members but then that makes it all worthwhile as a look through the data - so absorbing. ( No wonder the chores get left.........)

 

 

Palomar 232847 + 104119. Another group of 4, lurking just above the obvious triangle of stars and the faintest is mag 18.7 (at the bottom of the group)

What is interesting is the 18.7 galaxy appears to be connected by an arc of stars to its neighbour (needs a careful look) - this could be a distant VV (or an Arp) type classification?

 

Palomar 224346 +120335. Made up of 3 mag 17 and one mag 16 galaxy. Red shift for the mag 16  gave a distance of 1.165 billion lyrs away - hard to take that in.

 

Finally the show stopper 'sight of the night'

Palomar 003943 + 211056 with its 5 members, BUT which ones? The star is 54 Psc and the bigger galaxy group is Abell 75

 Here they are, close up. The group of three with the faint one on the right at mag 18.7, then just to the right (not the star) is a mag 16.8 and below it another mag 18.7.

Take a look to the left of the fov at the galaxy on the edge - it has a very interesting curving tail? - it shows up on high res images - another galaxy? a tidal star stream?

 

Tracking this lot down was quite demanding and well worth it. As a light relief I then did a couple of Hicksons and an Arp.

Mike

 

 

Edited November 13, 2020 by Mike JW

[Martin Meredith]

Sounds like a great night's work. I love tracking down these objects too, though I haven't done much of that recently. You never know what awaits, and the likelihood that only a handful of observers have bothered to check out any of these individual groups adds to the excitement.

Strangely, Abell 75 is one I visited last month, noting the ultra-compact PCG and the lovely chain of galaxies leading down from 55 Psc. Here it is in colour (doesn't add much!)

Martin

[Marvin Jenkins]

Wow. Such amazing work on objects so distant. I am full of admiration for your attention to detail and the information given. Such tiny blobs! But a whole galaxy! Blows my mind.

Marv

[Mike JW]

Thanks Marv - glad you enjoyed the PCG exploits. The universe is an amazing place, as is planet earth.

Martin - great to see your shot. When the view appeared on the screen I was awe struck - the bright stars and that gorgeous chain of galaxies. I just starred at the screen delighted and almost overwhelmed by the beauty of the view. I just let the subs keep coming in. (I dumped quite a few subs to keep the ones with the sharpest stars in unsteady skies) The PCG seemed somewhat irrelevant to the galaxy chain. At first they were a disappointment to the chain but then I zoomed in and found out the info. You too picked up the curving tail of the nearby galaxy.

Mike

[Mike JW]

PCG 114544+262426 in LEO. A group of 4 galaxies

What a lark PCG hunting is. It takes time to be sure I am at the correct spot - it is the tiny group to the right of the bright star

The zoomed in shot shows them better.

Now the interest really gets going. The four galaxies in the group are circled (mag 16/17). The bright one almost dead centre is about 1.39 billion lyrs away. No data on the other 3 members.

The left hand yellow line is Quasar - a mere 6.7 billion lyrs away (light travel time) and mag 20.3 - green filter.  The right hand yellow line is a quasar, a mere 7 billion lyrs away and mag 19.1

The three green lines point to mag 20 galaxies (measured through a green filter) - see NED data.

I find magnitude very confusing but get the point that it will be different depending on the filter used. Likewise distance does my head in when it comes to redshift data.

By the way, the bright star with the spikes is a red giant.

 

Mike

 

[Mike JW]

Here is PCG 115655+241600, also in LEO. This is a group of 5 galaxies and one of them has a redshift equal to about 1.7 billion lyrs away.

The image on the right is zoomed and some of the subs removed to help sharpen it up. The group are the obvious galaxies near the bright star . The various other fuzz spots are also galaxies.

 

 

 

 

 

 

 

 

 

 

 

 

 

Whilst looking at Aladin (with NED data overlay) I noticed various data points corresponding to non noise grey fuzz on my image. The shot below is even more zoomed in and further noise reduction and still fuzzy areas remain. They seem to coincide with data points on Aladin/NED. I have labelled with magnitude accordingly - I really do not believe I am picking up mag 21 or mag 22 ?????!!!!!!!

Even more unlikely is: the galaxy above the bright one if you look closely has two bright points - Aladin/NED show these two and one other as 3 galaxies - this must be some camera/optical aberration in my system? At this rate I shall be viewing beyond the universe!

[Martin Meredith]

Intriguing images. Looking at the Aladin SDSS9 layer I'd agree you've picked up these galaxies.

Theoretically, a 15" scope at F3.5 with a sensitive sensor ought to get below mag 20. I'm impressed that this is possible in so 'clean' a way in a mere 1m40s made up of 10s exposures. 

I can't see magnitudes for these galaxies on Aladin apart from GAIA estimates. What's notable about the GAIA data is that the G magnitude (corresponding not to green but to the broad spectral band: see https://www.cosmos.esa.int/web/gaia/edr3-passbands) are similar to the range you label, but red magnitudes that are somewhat brighter in general. The point labelled 20.2 has a G of 20.6 and a R of 18.5 (and a B band mag of 19.9), suggesting to me that it is a strong emitter in the red and quite possibly near-IR part of the spectrum, where our sensors tend still to be quite sensitive (eg Ultrastar is quoted at over 40% QE at 750nm). So it would be possible to pick up some galaxies at a given quoted magnitude and not others at the same magnitude, depending on where they are emitting most (and also on their redshift I suppose).

Looking at the GAIA passbands versus the Ultrastar, it seems the closest band is actually the GAIA B band (plus a little bit of the R).

Nice work! 

Martin

 

Edited January 24, 2021 by Martin Meredith

[Surreydocker]

Amazing ! >1 billion lyrs - that is mind-boggling ! 

I guess I'll need to move to the country if I want to see such things myself !!

Ian

[icpn]

Hi Martin

   there was this transform

V := G + 0.01760 + 0.006860 * (BPg−RPg) + 0.1732 * (BPg−RPg)^2

 to get from GAIA G to approx V for GAIA DR2. I don't know if it still applies to GAIA EDR3. However obvioulsy magnitude estimates that faint are going to have realtively large error bars and I spspect that ga;laxy magnitude estimates at that level should be treated as aprriximate only.

 

Owen

[Martin Meredith]

Thanks Owen. I was looking for such an equation a few years back and never found it...

Martin

[Mike JW]

10/03/21 - What to do on yet another rainy day - take a look at my recent PCG observations. As soon as I start calling up Aladin/NED and other data, time disappears so quickly. I become fascinated by what I can pick up in my set up - awed, yet again.

PCG 104737+423928 is found in UMa.  Four in the group (triangle tipped to the left), the bottom left is two galaxies. The four galaxies are not a true group. Top and bottom left are about 1.7Gyr away, the third (bottom right) is a mere 1Gyr away! (approx).

 

PCG 095352+571046 is found in UMa.  Four in this group but which ones? By checking the distances I concluded the ones with my lines are the group. The obvious galaxy at the top left is  further away. The other fuzz spots are galaxies as well.

PCG 104527+493118 is found in UMa. This is definitely a case of the more you look the more you see. I almost missed this group of four - they are near the top. I am glad I did not centre them because there is so much of interest in this shot.

Below is the close up of the group of four  I see five, well actually six and then of course there are those sneaky little intruders. The big six (wiggly line of 6) are all 2.2 billion lyrs away (very approx). The intruders (3 of them - 2 one side, 1 the other side of the bright galaxy - no data)

Now there is that big obvious galaxy to the left of centre - UGC 5972 - not exactly near to us at 460 million lyrs away, SBbc is its classification. See below and yes you have guessed the fuzz spots are yet more galaxies with no data.

There are yet more faint galaxies in the big view which I did also check out.

PCG 094316+392308 is found in LMi.  I soon got distracted when the wide fov appeared on screen ( the excessive noise is because there was high thin cloud lurking). The  large obvious galaxy caught my eye before I saw the PCG candidates. Here we go again, info says 5 members but I see 6 (maybe 7)

Close up below , clearly shows 6 members in a sort of Y-shape.  The obvious brightest galaxy lies around the 2 billion mark. No data on the others.

The large extended V- shape of fuzz spots appear also to be galaxies.

Then there is UGC 5193 - a large elliptical  and has it interacted with its neighbour to the right - something is on the go. The trouble is they are separated by about 23 million lyrs. So maybe there respective halos are a overlapping due to line of sight?

Finally the stretched S-shape - bottom right - yet more galaxies ( not all of them)

 

 

Much interest, pleasure from pursuing these galaxy groups.

Mike

 

 

 

[Martin Meredith]

Some great observations there Mike. Love the edge-on in the penultimate picture. Although your FOV is quite small, it gives the appearance of a much wider field, I think because of the different galactic sizes on view providing a sense of perspective.

Some of them may have been observed only once or twice before! (I was going to add 'or never', as they were discovered using an algorithm, but I'm pretty sure they would have been carefully checked!).

I remember reading some years ago that the criteria for choosing compact groups placed a limit on the magnitude difference between the bright and faintest members considered to be part of the group and there will have been other criteria (compactness too, of course), so the existence of other galaxies in the region may well indicate physical proximity yet escaping being considered members of the group for purely algorithmic reasons. Also, I think they excluded one of the two overlapping groups if they algorithm came up with such sets.

The PCGs were apparently collected to extend out to greater distances the kind of catalogue Hickson represents. 

Martin

[Mike JW]

I thought it was time I went chasing a few of these groups rather than the bright DSOs.  I was in Leo last night so here are three offerings.

PCG 114333+215356 - a tiny group of 5 galaxies easily lost amongst the field stars. A very lonely group but they form a 'smile'  pattern in the view.

PCG 115120+273803 is another group of five. The fov is delightful. The two obvious galaxies nearby are PGC 37109/10 and I decided to leave the bright satellite trail just to remind us all how us humans are now further wrecking the night sky.

 

PCG 115517+232335  resides in Abell Cluster 1413. In the wide fov, if it looks like it could be a galaxy, then it most likely is one - they are everywhere.

I think the group of five are the ones that form a V-shape in the centre of the close up. I am fairly certain that all the fuzz spots in the close up below, are galaxies.

Mike

 

[Mike JW]

I visited a few more PCGs a night or two later in Coma. PCG 123002+273422 - there they are lurking in the line of stars - lovely sight.

PCG 123439+234951 is a delightful group of galaxies in the centre of the fov.

[Martin Meredith]

Hi MIke

By a strange coincidence I was also observing one of these PCGs earlier in the week, except it was called SHK 204! It has 13 listed members of which what looks to me like the faintest (near the centre) is mag 20.4 (B filter). Most of the group is listed at just over 2 billion LYs away but that faint member is given at nearly 6 (I'm never sure how accurate the measures are but if so this is an interesting interloper).

 

I generally start off in monochrome but if there are several brightish stars my curiosity as to their spectral class gets the better of me and I add a few RGB subs at the end. From L to R we have G8V (mag 12.8)+G2 (mag 10.4) (this is double star COU 594 with a sep of 2.8"), F2 (mag 10), K01V (mag 8.6) and K4III (mag 9.7). This is a linear 'stretch' with saturation turned right up. SHK 204 is completely invisible with the linear stretch. Its like having 2 images in one, part of the fun of interactive observing! 

I did wonder whether these 4 stars which forms such a perfect curve are part of a grouping. They really are gorgeous and must be impressive visually. Now digging a bit deeper I see that (at least some of them) are part of the huge Melotte 111 grouping that dominates Coma (and which is large enough to contains several other SHK groups). The distance ratios in these fields always gets me.

 

Martin

 

[Mike JW]

Thanks Martin for adding in the extra info. Even better that I got a 'spot one, get one free' - I had not thought to check if it was also a SHK. If it wasn't such a faff, I could have taken the camera out and popped in an eyepiece to enjoy these stars visually (would have to wait a few minutes to dark adapt).

Below is the full fov - what an interesting area - all sorts of faint stuff lurking.

Mike

[Mike JW]

August 3rd.  PCG 232342+163117 lies in Pegasus, in a busy field of galaxies. The four components are mag 18/19 galaxies.

Mike

 

[Mike JW]

My first reaction to seeing PCG 232329+173715  in Pegasus appear on the screen was 'no way - you're having a laugh!' What do you see? - yep 1 galaxy and 3 stars. However go onto Aladin and sure enough the 3 stars are galaxies - no other info - tight galaxies. could they be ellipticals? In fact Aladin shows the main galaxy as having a companion but my diff spike has covered it up.

 

Mike

[Mike JW]

This time I visited a couple of targets in Aquarius.

PCG 221755-013227.  Yeah, I know its just a collection of little fuzz spots. The brightest is mag 18.6 in the centre and the other 3 are mag 19.. They are not a true group. The central gx is about 1.57 Gly and the topmost one is a mere 1.86 Gly.

PCG 222121+002743 - at first glance I thought they were stars. The two brighter gx are around the mag 17.6.  and are very distant from each other. Top one is 0.860 Gly and the lower one 2.7 Gly. To the left the mag 18.6 is way out there at 3.4 Gly. Look carefully to the right of the lower bright gx, close to and just inside the red line is the fourth group member at mag 18.7 and a mind blowing 7 Gly away.

Mike

[Mike JW]

Well, here I am again. It has been three months since I had some PCGs to post. The collection below are found in Cancer.

PCG 091133+291646 - a group of 4 galaxies near to a pair of stars? or are they. The brightest of the four has a red shift somewhere in the 1.3-1.4 Gyr and at mag 18. Its fainter companion is mag 19 and the other two are mag 18. No other info for these three galaxies. In colour images the two stars are very orange and NED gives the lower one as being a galaxy. The mag 19 quasar is at a similar distance. However the other labelled quasar lurks around the 10 Gyr - just blows me away!

PCG 091524+213038 is a group of five galaxies which might be a true group as they are all of similar redshift (approx 1.7Gyr). Some of the other fuzz spots in the region are also at a similar distance.

PCG 090155+323620 is a group of four, yet we have 5 objects making up a V shape. NED suggest all five are galaxies and in fact the middle fuzz spot on the right (slightly extended in this shot) is actually two galaxies and one other object. Only one of the group has a redshift value which equates to the 1.2/1.3 Gyr distance.

This group wins the award for the most interesting shape and we have the obvious additional galaxy above the V.

There is one other PCG in Cancer but conditions deteriorated so I shall have to visit at a later date.

Mike 

[Marvin Jenkins]

Completely ridiculous! Blows you away? My tiny mind fried. Amazing work. 
M