Martin Meredith

This thread is getting quite long now so I'm not sure if we've already seen this one... Here are two Arps in Cetus for the price of one. Arp 133 is the elliptical just left and up from the centre. This is NGC 541. Arp classified it as 'Elliptical with nearby fragments' and one can see why. The faint companion at 9 oclock is a mag 17.2 galaxy and this, together with the rest, look like a superimposed but more distant galaxy chain. However, the SDSS view on Aladin tells a different story. While the 9 oclock companion is clearly galactic (but no more distant than the elliptical), the largest of the others is distinctly blueish. They are classified as 'clumps' of molecular gas and each clump has its own identifier. Delving deeper, it turns out that the clump at 10 o'clock is Minkowski's Object, nicely described in [1]. The origins of this object are still under debate (see [2] for a recent study). One suggestion is that is is a dwarf galaxy that is interacting with a radio jet from NGC 541 (and possibly from NGC 547 which is also a radio galaxy). The other is that it formed in situ from a gas cloud between NGC 547 and 541. In either case, the argument goes that it is being pushed to star-formation by a jet (possibly coming from a black hole in one of the two radio galaxies), hence its blueness. NGC 457 is the lower of the two galaxies (the other is NGC 545) making up the obvious 'double galaxy', Arp 308 (aka VV 963). As if that were not enough, the field is replete with spiral galaxies, mainly S0 types. Is it a coincidence that 5 of them have exactly 90 degree inclination (ie seen edge-on), or an artefact of some algorithmic processing? The galaxy with most visible structure is NGC 538 at the base of the shot. This is of type SBab(bar). This extended group is part of Abell 194, a close galaxy family centred on UGC 996 but so close as to be too large to fit in my FOV 😞 Martin [1] https://sigmaorionis.wordpress.com/2011/07/19/minkowski’s-object-arp-133/ [2] https://arxiv.org/pdf/1703.03006.pdf

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

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

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

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

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

Its fascinating to revisit old captures to seek out new details. I definitely don't have the mag 20.9 quasar in my image although the other two are pretty bright. The last two nights I have been exploring distant quasars (z > 4) and managed to pick up a z = 4.26 at mag 20.1 and just possibly a 4.36 at mag 20.9 (right on the edge of detection). I'll post about those in a separate quasars thread! What your last post illustrates is one of the main differences between EEVA and AP: interactivity. There are some stretch settings that bring out certain details but leave the rest of the field looking ugly, and others that lose the details but produce a cleaner overall appearance. We need both! The rings look very clear in your log stretch case. That reminds me that I'd really like to implement a 'standard' stretch that can be applied to any image to enable comparisons. I'm thinking of something like the one used in the de Vaucouleurs Atlas of Galaxies which is essentially a log stretch from a photometrically-defined baseline (so the pixel values can be compared across images). Martin

Here's a packed galaxy field in Pisces displaying a great range of galaxy types as well as Arp 229 (to the lower right), all circling the mag 7.6 star HD 8347. Arp 229 belongs in the 'concentric rings' category, this designation applying to the brighter of the pair, E-S0 type NGC 507. The fainter member is the elliptical NGC 508. They're also members of the overlapping galaxies catalogue due to the proximity of their outer halos. The close-up of the lower part of the field also shows S0 type NGC 504 which is seen exactly edge-on (inclination 90 degrees) with a position angle of 45 degree, so somehow meets the Platonic ideal for galaxies... I'm trying and failing to visualise the cause of the curve in the rightmost spiral arms of this galaxy. Interaction? The distance estimate of 205 MLyrs is similar to NGC 494 but lower than most of the other galaxies in this field (~265-285 MLyrs). NGC 494 is a type Sab with an 83 degree inclination that is just right to see the spiral arms. The upper part contains 4 further NGC galaxies and a range of slightly fainter galaxies. NGC 501 is a compact elliptical while the bright NGC 499 is type E-S0. NGC 496 is Sbc although the structure is a bit fuzzy in this image. NGC 495 is the star here with the classic bar, type S0-a (bar). Again, the distance estimates cover a range from 210-260 MLyrs. Martin

Here's my Arp 314 which doesn't add much. I've been exploring the effect of different stretches on this one. Hyper definitely helps bring out the contrast between the core regions of the galaxies and the surrounding parts. The fact that my exposure duration almost matches yours is a complete coincidence. I left it running to see if I could bring out some of the faint arms and also to catch the fainter fragment to the lower left of the galaxy pair. This was one of 8 Arps I looked at last night out of a total of 33 objects over the course of a long 3h40m session, taking advantage of better-than-poor seeing, no moon, and a fortunately inaccurate cloud forecast! Martin

I don't think I've observed Arp 314 but it looks really interesting, especially with that strange detached arm (?) to the S. The Arp Atlas notes how extremely faint some of the structures are. You did well to pick up a hint of the SE tail. I'll see if I can make it out tonight, assuming transparency is better than last night... Meanwhile, here's Arp 3 from this time last year. Like all low SB galaxies it is somewhat frustrating with its amorphous and ill-defined shape, but there are some interesting features. The photo in the Arp catalogue has much more structure. Martin

According to Aladin, that is the Mira-type variable star V571 Vul. There's some info (in German) here: http://www.astro-photos.net/CCD/M27_cctv.html which Google translates to: In the northwestern part of M 27 there is a long-period variable Red Giant of the Mira type. It changes its brightness from 17.5 mag to 14 mag with a period length of 214 days. The official name is V571 Vul, the 571st variable star discovered in the constellation Foxes (Latin Vulpecula). The star discovered in 1990 by the Czech amateur astronomer Leos Ondra is known under the much prettier name Goldilocks Variabler. The history of discovery is also pretty. Two astronomy magazines published a picture of M 27 on their front pages, but they were taken at different times. Ondra noticed that a red star was shining in one shot, which was obviously missing in the other shot.

Great to see some comets. 67P has quite a tail. Is that also the stub of a tail in 29P or perhaps it is moving sufficiently quickly to produce a slight egg shape? For C/2019 L3 it is easy to see why Messier felt it necessary to produce his catalogue... Martin

That is an excellent image, showing much better detail than mine. I wonder how much of that is down to resolution, seeing or tracking differences. The closest galaxy I can see if NGC 4716, about a degree away but at 134 MLys compared to 178 MLys for Arp 15. This paper lists NGC 7393 as not having a companion: http://articles.adsabs.harvard.edu/pdf/1985ApJS...57..643D Martin

Maybe this part of the sky contains some kind of magnitude booster... Great to see some z > 3 quasars. Coincidentally I'd just added some z ~ 4.5 quasars in Pegasus to my target list for this evening. Martin

Thanks for checking on NED. The use of different filters for the reported magnitudes can often explain differences like these, but not in this case. Now, your behemoth might be able to pick up mag 21.... I'll repeat the exercise on another cluster (hoping for a couple of clear nights tomorrow and Friday). Martin

Here's Abell 2510 in Pisces. This is not one of those impactful galaxy clusters -- the galaxies are very faint and understated, and dotted around the field. This is a distance class 6 cluster and I'm often intrigued when there is nothing marked on the charts to see if I can pick up any galaxies. I've marked some of the galaxies for which I have data and which are just about visible in the image, but I find it difficult to believe the data. The galaxies are to the lower left of the label in each case. From top to bottom we have 5186886 4104 MLyrs, mag 20.3 5186892 2373 MLyrs, mag 19.5 5186887 4200 MLyrs, mag 20.8 3576831 1603 MLyrs, mag 19.4 5184351 5726 MLyrs, mag 21.8 3334273 2738 MLyrs, mag 18.7 These are all B filter magnitudes. I'm pretty sure there's no way I can detect a mag 21.8 (or even a mag 20.8) with my kit, even with 8m of exposure! The distances marked show an incredible spread too. It would be interesting to see more shots of this and to try to get alternative distance/mag estimates...

I don't think we've had Arp 15 yet. This emission-line galaxy (NGC 7393) lies in Aquarius and is also known as VV 68. It has an unusual appearance rather like the head of an owl seen at an angle. Arp classifies it as a "spiral with detached segments". The type is Scp D, something I've not come across before. Schroder & Kepler (1991) describe it as SB(rs) cP. I guess the p is 'peculiar'. More alphabetic soup to figure out!

Although it is more than 30 years old now, the 1990 paper New observations and a photographic atlas of polar-ring galaxies by Whitmore et al [1] makes for fascinating reading and inspection, containing as it does a catalogue and images of over 150 such polar ring galaxies (PRG), candidate PRGs, and other similar-looking and possibly related objects. The catalogue lists 6 confirmed PRGs (category A), 27 probable PRGs (cat. B), 73 possible PRGs (cat. C) and 51 objects that might be related to PRGs, or are unrelated but could be mistaken for PRGs (cat. D). This latter category includes 'box, peanut and X-galaxies' (the latter like NGC 128 above in this thread), smoke-ring galaxies, Hoag-type and Mayall-type galaxies, and superpositions that just happen to look like PRGs, amongst others. The paper is well worth a browse, though following objects up with more recent observations is necessary as I imagine some of the objects will have changed category by now. I observed 5 members of this catalogue last night, 3 from cat. C and 2 from cat. D. and include 4 of them below (one was lost in the murk). PRC C-71 in Pisces. This is labelled PRC 141 in my image (as I made a quick catalogue from the paper and haven't yet sorted out all the proper names). This is a possible PRG showing the x-structure, but could also be a chance superposition like D-49 below. It really is not clear either from the DSS image on Aladin which interpretation is correct. Contrast the above with PRC D-49 in Aquarius. This is regarded as a 'superposition that resembles a PRG'. The superposition of the two galaxies is really clear here. The galaxy 'pair' is listed at b mag 18.6 but looks much brighter to me. Some of the outer parts of the larger spiral can be made out. One wonders what the actual relative distances of these two members are and what the chances are of a near-perfect line of sight superposition with the galaxy centres lining up like this. D-49 is a member of Abell 2258. I found this chance alignment one of the more fascinating observations I've made using EEVA. PRC D-32 in Capricorn (not shown) at -23 degrees dec was too low for me to make out any details. I might revisit this on another day, although the DSS image is not much to write home about. PRC C-66, also in Capricorn at a healthier -16 degrees dec, was one of the surprises of the night. Individual subs showed no hint of anything exciting, but as the stack built up a clear long tail to the south appeared followed by hints of a multiplicity of short counter-tails to the NNW and a possible double-core in the galaxy itself. The SDSS image on Aladin also indicates 2 core-like nuclei and shows the upper tail to undergo a sharp 90 turn to the left (WSW) which then of course becomes obvious in my image... This is a member of Abell 2150. The most confusing field of the night is the one containing PRC C-58 (labelled PRC 90 here), also in Capricorn. This was captured through bushes at an altitude of under 20 degrees (decl. -25) so the shot is pretty grainy. The description in the catalogue is a little contradictory because PRC C-58 is identified with NGC 7016, but the text suggests the candidate is actually the double-core object near the centre of the shot (NGC 7017). There is an almost mirror-image double galaxy/galaxy pair to the north of the shot too (one member is NGC 7018). NGC 7017 + 7016 is classified as VV 1906, while NGC 7018 is VV 764. These are all members of Abell 3744. It turns out that NGC 7016 and 7018 are radio galaxies near the centre of the cluster. Article [2] describes them in great detail (= I've only skimmed it!). There are some fascinating structures visible at those wavelengths. In the visible wavelength image of this field in the 1990 article there is a hint of a jet to the lower right of NGC 7016 (terrestrial SE, astronomical SW) -- confirmed, I believe, in [2] -- that looks like it would be a challenging object to capture using EEVA techniques if anyone lives at a sufficiently southerly latitude! I'll certainly be revisiting this catalogue as the season progresses and will be happy to make the catalogue available when I've tidied up the names. Martin [1] http://simbad.u-strasbg.fr/simbad/sim-ref?bibcode=1990AJ....100.1489W [2] https://research-information.bris.ac.uk/ws/portalfiles/portal/39386034/1312.5311v1

Mike, I tried to improve upon your shot of NGC 7428 but didn't get anything better. Its pretty murky for me in that direction too and until I trim the summer growth I was also observing through gaps in a philadelphus (or similar).... remarkable that one can get anything at all that way. My NGC 125/128 is also no improvement, but was very enjoyable to observe. I also followed your lead and looked at IC 5285 with its remarkable ring. Here's a stretched shot to bring it out more clearly at the expense of background noise. Also in shot is NGC 7489 which is really ragged, with spiral arms splayed out all over the place to the N. This is type SABc or Sc and, like the ring galaxy, is at about 300 MLyrs distance. In the SDSS shot it looks quite blue, as does the ring in IC 5285. Here's my take on the wonderful NGC 7217 Martin

That's a great find. The middle galaxy looks like it has been through the wars. I was also looking at a few VVs last night in Pegasus. I spotted this one thinking that the surrounding galaxies would make a good setting, and indeed there is a lot going on here, apart form the relatively rich star field. Not an NGC or IC in sight, but a variety of UGCs and fainter on display. VV 1955 is the indicated pair (SW of the label) at around 323 MLyr. The other galaxies are at a similar distance, so this looks to be a genuine grouping. I imagine it has a WBL listing too but haven't yet tracked it down. There are a lot of close (optical?) doubles in the centre of the image making it look like a stacking error, but they are genuine.

IC 1525 is beautiful in this shot: bright core, moderate halo, faint spidery outer arms -- wonderful. For me this is what makes EEVA so interesting, visiting a target perhaps for the first time and seeing a galaxy such as this one appear. Martin

Thanks Mike. Here's another similarly-compact one acquired nearby: SHK 331. This one has 7 listed members but I can only see 6. Aladin shows an additional 2 tiny faint galaxies but I suspect these are not members of the group as originally listed by Shakhbazian. Mags range from 16.3 to 18.7.

Here's SHK 332 in Aquarius from last night, first as a 'wide' field (0.44 degrees across!) for the usual spot-the-Shakhbazian competition, and then zoomed in This is a line of 5 mag 18.5 to 19.1 galaxies within less than an arcminute, with a slightly brighter one (m 17.8) off to the side and a further member on the line. I've also marked a mag 20.0 (B filter) galaxy (PGC 96884) below the group. Not a lot more to say about this group apart from its aesthetic merits as a near-chain! Martin

Not cheap but the best book I've seen by far is Astronomical Image Processing by Berry & Burnell. It comes with software but even without the disc it is worth it. I have the first edition. It may not cover everything that you'll find in software, but it goes a long way and is the only source I've found that starts with the fundamentals. Martin

Well, you did say "SNR improvement is higher than most other down sampling methods" which is the claim I'm looking for hard evidence for. I must say I'm skeptical -- if binning is really so good one does wonder why most/all image processing software uses lowpass (spatial) filtering prior to downsizing. Or is aliasing not a problem for astronomical images? Anyway, further apologies to oymd for going off-topic and maybe this can be pursued elsewhere if it is felt to be worth pursuing at all -- I kind of doubt it as I've come across the "astronomical images are (magically) free of all Nyquist constraints" several times and the matter never seems to be resolved! cheers Martin