Galaxy of the Month Archive 2018

In this series of articles we draw your attention to galaxies particularly worthly of an observer's time.

• NGC 1024 in Aries

  December 2018 - Galaxy of the Month

  

  NGC 1024 is part of a group of three galaxies, including NGC 1028 and NGC 1029.

  First discovered by William Herschel in 1786, NGC 1024 was included by Arp in his catalogue of peculiar galaxies as number 333, under the classification of Miscellaneous galaxies. Arp classified it as such because it had very thin spiral arms coming from a pseudo ring. As such it does have the very complex morphological classification of (R')SA(r)ab. NGC 1028 and NGC 1029 are very much fainter and were first discovered by Albert Marth using William Lassell’s 48” reflector from Malta.

  There are some issues over whether the group is physically related and it is included in the WBL catalogue as number 82. The WBL group only consists of these three galaxies. Just to show how confusing cataloguing groups of galaxies is, the NGC 1024 group is also included in the LGG catalogue as number 69. The LGG group also makes the group count as three galaxies, but in this case NGC 1024 and NGC 1029 make the cut and NGC 1028 is dropped from the group to be replaced by the elliptical galaxy NGC 990, which is over a degree away on the sky.

  If you look at the redshifts of the galaxies then the redshift for NGC 1028 is more than twice that for NGC 1024 and NGC 1029, whilst that for NGC 990 is pretty much the same, as always showing that proximity on the sky is no substitute for proximity in space.

  At the very least NGC 1024 is thought to form a physical pair with NGC 1029. NGC 1029 is classified as a lenticular galaxy whilst NGC 1028 appears to be a Sa spiral.

  The NGC 1024 group is thought to be about 158 million light years away.

  Visually NGC 1024 will be challenging in 20-cm but should be visible relatively easily in 37cm. The companions are going to be a challenge I think for 37cm and may require 50cm to see easily. The three NGC galaxies are a tight group and you may need to use medium to high power to cleanly separate them.

  For masochists there is also a much fainter (16th magnitude) galaxy in the field known as LEDA 1385855. Steve Gottlieb suggests that even in his 17.5” both NGC 1028 and NGC 1029 are pretty faint.

  There is a 7th magnitude star close by the group which will need to be kept outside the field in order to pick up the fainter members I would think.

  Owen Brazell - Galaxy Section Director

• NGC 584 in Cetus

  November 2018 - Galaxy of the Month

  First discovered in 1785 by William Herschel, NGC 584 is an elliptical galaxy with a morphological classification of E4 in Cetus. It is accompanied by the spiral galaxy NGC 586, also discovered on the same night by William Herschel.

  NGC 584 is also noted as IC 1712 as Barnard found it whilst observing the comet C/1888 R1 – one of his discoveries. He sent a note to Dreyer about it but then realised that it was NGC 584, which he neglected to tell Dreyer so the observation was added in as IC 1712.

  Although NGC 584 is classified as an elliptical there is growing evidence that it may in fact be a lenticular, and in fact in the de Vaucouleurs Atlas of Galaxies (CUP) it is given as an example of an SA0-.

  NGC 584 is part of a small group of about 8 galaxies catalogued as LGG 27 which also includes the galaxies NGC 586, NGC 596, NGC 600, NGC 615 and NGC 636. Most of the galaxies in this group are ellipticals or lenticulars. It is worth noting that other resources put the number of galaxies in the group as high as 11. William Herschel has the honour of discovering all the NGC galaxies in the group.

  The group is only about 20 Mpc away from us and is spread quite widely across the sky with about 2 degrees separating NGC 584 and NGC 636. SIMBAD suggests NGC 584 is part of a pair of galaxies (one assumes with NGC 586). NED does not have this so I guess more work to be done, although NED does reference a paper which does suggest that NGC 586 is the companion. The pair are not obviously interacting. The NGC 584 group is also part of the Cetus II cloud.

  Observationally, given that William Herschel found all these galaxies, they should not be that much of a challenge to find. NGC 584 itself is part of the Herschel 400 listing and O’Meara also has it has it as number 6 in his book of Hidden Treasures.

  NGC 584, NGC 586, and NGC 596 should all fit in the same field of view of a modern hyperwide eyepiece at a medium power (say 160x). O’Meara suggests they are all visible in a 4” telescope, if you are at 7000’ up a mountain and in pristine skies. O’Meara also carries on the fashion of naming everything by calling NGC 584 the little spindle galaxy. Experienced galaxy observer Mark Stuart finds it only just visible with his 10” SkyWatcher from moderate skies in the UK.

  For those who do not feel that NGC 584 is enough of a challenge then there are a number of other fainter galaxies in the area that will be a challenge for larger telescopes, including IC 127 and LEDA 1028168.

  Owen Brazell - Galaxy Section Director

• NGC7385 in Pegasus

  October 2018 - Galaxy of the Month

  Staying in Pegasus for another month, we look at the small group of galaxies surrounding NGC 7385.

  The New General Catalogue of Nebulae and Clusters of Stars (NGC) lists eight galaxies in this area, with the group also known as WBL 688. The two brightest galaxies, NGC 7385 and NGC 7386, were discovered by William Herschel in 1784. The rest may have been discovered by the Rosse team in 1850. However in the accompanying chart some of the numbers are incorrectly attached to galaxies when it would seem that the Rosse team actually only saw stars. So the numbers for NGC 7384 and NGC 7388 appear to have been randomly assigned to galaxies that were not actually seen by the Birr observers, but by later researchers.

  Strangely, most modern references point out that these observations were just stars, so I am not sure who assigned the numbers to the galaxies. The compilers of the Revised New General Catalogue (RNGC) in this case do not seem to be guilty as they also refer to them as stellar. It seems that it was the compilers of the original Principal Galaxy Catalogue (PGC) in 1989 who were responsible for assigning these faint galaxies to the NGC numbers.

  The WBL 688 group only lists 6 galaxies as physically associated in this area: NGC 7385, NGC 7386, NGC 7383, NGC 7389, NGC 7387 and NGC 7390. The group would appear to be at a distance of about 100 Mpc and to consist primarily of elliptical and lenticular galaxies. I wonder if this is the core of a fossil cluster. NASA/IPAC Extragalactic Database (NED) also lists the brighter galaxies as part of ACO 2506, which I struggle to understand, in fact discussions with Harold Corwin indicate this is an error.

  When you look at deep images of NGC 7389 it does look just like a barred spiral galaxy, just without any obvious signs of new stars. This is in essence what lenticular galaxies are. They have the light distribution of spiral galaxies but no gas to make new stars. In this case NGC 7389 would be classified as an SB0 galaxy. NGC 7383 also looks very similar and is also classified SB0, although it does not show such a well developed bar. These shapes do not show up well on the DSS images but do on the SDSS and PanSTARRS images.

  NGC 7385 appears to have radio jets, and in one of those an HII region has been detected at radio wavelengths which may be caused by the interaction between the jet and the ISM: one would not expect to see HII regions in a normal elliptical galaxy. Strangely SIMBAD refers to NGC 7385 as a quasar and, although it is certainly some form of AGN, most references suggest it is a low power one. NGC 7385 was home to SN 2005er.

  The group is fairly tight and most of the galaxies will fit in the field of a modern high power hyperwide field (100 degree) eyepiece. It would appear that a 16” (40-cm) telescope will show five of these galaxies in this field, so I guess that the challenge for owners of larger telescopes to see more of the cluster.

  If you wish to know more about this group then Mark Bratton published an excellent article on observing it in DSO 168, and for further reading on the observations by the Birr team see Wolfgang’s excellent book on Observing and Cataloguing Nebulae and Star Clusters.

  Owen Brazell - Galaxy Section Director

• Hickson 93 in Pegasus

  September 2018 - Galaxy of the Month

  The discovery history of the objects in the quintet of galaxies catalogued as Hickson 93 is a run through of some of the great visual observers of the 19th Century.

  The brightest galaxy in the group, NGC 7550, was discovered by William Herschel in 1784. The next brightest galaxy in the group, NGC 7547, was discovered by his son John when revisiting his father’s observations.

  Bindon Stoney, one of Lord Rosse’s assistants, discovered NGC 7549 in 1850 using the 72” telescope at Birr. Lord Rosse and his team also glimpsed another galaxy in the area which was added to the NGC as number 7553. Its position was not well defined and this galaxy was later catalogued as CGCG 454-14 by Zwicky from the POSS plates. (CGCG stands for Catalogue of Galaxies and Clusters of Galaxies). This object is almost certainly the one seen by the Birr observers.

  The last of the group to be discovered visually was NGC 7558 by Albert Marth using Lassell’s 48” reflector in 1864, it may however have also been seen by the Rosse team 14 years earlier as they described a fifth nebula in this group.

  The discovery history gives an idea of the challenge required to see all the galaxies in this group.

  Halton Arp in his famous catalogue of peculiar galaxies added the pair NGC 7549 and NGC 7550 as Arp 99. Arp thought he could see indications of an interaction between the two due to the shape and length of the spiral arms on the opposing sides of NGC 7549. There has been some debate as to whether Arp meant NGC 7549 or NGC 7547 as the spiral component of Arp 99 however it seems fairly clear from his description that it is NGC 7549 that should be the other component of the pair. Deep images also show shells of material around NGC 7550 and NGC 7547. It is likely however that NGC 7547 is part of a physical triple system with the other two.

  The group is interesting as it seems to consist of three spirals, one lenticular and one elliptical and many of the galaxies are obviously interacting. It is not often you see lenticular galaxies outside large galaxy groups however Hickson groups are often thought to be conglomerations within large loosely bound galaxy groups. In this case the group has a listing as WBL 700, although only 4 out of the 5 galaxies in HCG 93 are listed in this group in NGC 7547, NGC 7549, NGC 7550 and NGC 7553 (CGCG 454-15 on the chart). NGC 7558 may just be a line of sight object and not a physical member of the group, although to be fair Hickson did recognise this.

  To see more than the two brightest members of the HCG 93 group is going to be a challenge, except from very dark skies, and even then, a telescope with an aperture of at least 40cm is likely to be needed. The galaxy group will benefit from using medium to high power when observing it, as well as keeping any extraneous light from reaching the eye, in order to find the fainter members.

  If Hickson 93 is not enough of a challenge then less than half a degree south east is the galaxy group Hickson 94. This will be much more challenging. The galaxy cluster Abell 2572 is also close by. Although ACO 2572 is not a particularly rich cluster it does contain four NGC galaxies. The whole area is worth spending some time in. There is a nice drawing of the group at SkyInspector.

  Owen Brazell - Galaxy Section Director

• NGC 6926 in Aquila

  August 2018 - Galaxy of the Month

  With August finally comes the return of astronomical darkness at northern latitudes. For galaxy hunters though this is still a tricky time of year as the Milky Way with its nebulae and star clusters is still the dominant feature of the night sky and we have to look for galaxies skulking around the edges.

  This month’s challenge is NGC 6926 in Aquila. Discovered by William Herschel in 1784, NGC 6926 is part of a pair of galaxies with NGC 6929, a much fainter galaxy found by John Herschel in 1827 whilst he was checking his father’s observations. In 1784 when William Herschel found NGC 6926 he was still using the large 20’ in Newtonian mode. I wonder if he would have seen NGC 6929 as well if he had been using it in front view mode which would have allowed him to see objects up to a half magnitude fainter.

  NGC 6926 is a very disturbed looking galaxy and made the VV list of peculiar galaxies as VV621. I wonder why it did not make the Arp list but I guess so many galaxies and so little time to classify them all. NED does list NGC 6926 as part of a pair and although it does not explicitly state it is paired with NGC 6929 this is the most likely option. It also has these two as part of a poor group of galaxies which also includes UGC 11585 about 18’ away, and possibly others. The group is at about 82 Mpc from us and at that distance NGC 6926 would be substantially larger than our Milky Way.

  NGC 6926 is an active galaxy of the Seyfert 2 type. It also hosts an H₂O Megamaser in its nucleus. Megamasers are a very rare phenomenon with only 150 or so known. They come from the disk surrounding the central Supermassive Black Hole (SMBH).

  Images show that NGC 6926 is very distorted, perhaps by a gravitational interaction. Interestingly GALEX images show that both NGC 6926 and UGC 11585 are undergoing a burst of star formation as they radiate very strongly in the UV, so perhaps NGC 6926 is interacting with that one, rather than NGC 6929. NGC 6929 is a lenticular galaxy so it has no gas for star formation to occur, but it does not appear distorted in anyway.

  

  NGC 6926 and NGC 6929 are quite close together so high power will work in bringing them out. You can get UGC 11585 in the same field by using a medium power. For those that like collecting lists then NGC 6926 is part of the Herschel 3 list.

  The northern arm of NGC 6926 appears to have several knots in it, although I expect that visually these will be beyond all but the largest telescopes in amateur hands. Perhaps not surprisingly it does not appear in any of the standard guides.

  There is a nice amateur image at Astro-Cooperation, but in general as you can imagine this is a very overlooked galaxy. NGC 6929 appears to have another galaxy involved in its halo, although I think this will be too faint for anybody.

  Owen Brazell - Galaxy Section Director

• NGC 7242 in Lacerta

  July 2018 - Galaxy of the Month

  In terms of deep sky observing the month of July in the UK is not dissimilar to June in terms of observing opportunities, really a time to wash the telescope mirrors and sort out any niggles before Astronomical dark returns in August.

  My target for this month is one therefore rather more of hope than expectation and is the elliptical galaxy NGC 7242 in Lacerta.

  First discovered, although not reported, by Augustine Voigt in 1862 using the Foucault 80-cm silver on glass reflector at Marseilles observatory it was actually first reported by Stephan in 1873 using the same telescope. Voigt’s observations were not actually published until 1987!

  NGC 7242 is a cD galaxy at the centre of a small group of galaxies catalogued as WBL 679, which seems to contain between 4 and 9 galaxies depending on the source used. The other galaxies in the group are NGC 7240 (discovered by Stephan in 1873), IC 1441 (discovered by Bigourdan in 1889) and UGC 11963 (Also known as IC 1591 discovered by Barnard in 1888.)

  Barnard actually found three new nebulae in this field that have been assigned the numbers IC 5191, IC 5192 and IC 5193. Unfortunately, he did not send positions to Dreyer just a drawing so it was unclear which was which and the designations were only tied down recently after historical work.

  There is another IC object here as well, IC 5195 found by Bigourdan which turns out to be a galaxy very close to NGC 7242. Barnard did not see this so it will be tough to find and require high power and steady seeing.

  For those of a historical bent the original logbooks from Lick Observatory have been digitised and are available at The Lick Observatory Historical Collections. If you are interested in Barnard’s original observation of this group it was made on the 5th Dec 1888 with the 12” refractor and the drawing is there.

  The group is going to be challenging because NGC 7242 itself is only about magnitude 13.9 and the rest are fainter, it does show however what a good observer Barnard was in that he saw six objects in this field with the 12” refractor, even though he was observing from Mt Hamilton at 4265'.

  There was a supernova in NGC 7242 in 2001 which was independently discovered by Mark Armstrong and Ron Arbour in the UK (SN 2001ib). As expected from a supernova occurring in an elliptical galaxy it was a type Ia.

  Most of the galaxies in the group are elliptical or lenticular with the exception of IC 1441 which is spiral. Even IC 5191 which looks like a spiral is actually a lenticular. The group would appear to be about 300 million light years from us.

  NGC 7240 is also catalogued as VV 1936, and IC 1952 as VV 1935, so they were thought to be disturbed systems. I suspect these may be bad classifications as I suspect that what they thought were other galaxies were actually stars near the galaxies. Even Barnard was not able to resolve the stars from the nebula when he observed IC 5192. Note that because of the vagaries of software authors some charting software may show the Barnard IC numbers and some may not.

  Luginbuhl and Skiff (L&S) suggest NGC 7242 and NGC 7240 can be seen with a 25cm telescope, but I suspect this is from altitude and at least 30-cm will be required from the UK. Probably 45-50-cm will be required to see any of the others.

  Owen Brazell - Galaxy Section Director

• M101 in Ursa Major

  June 2018 - Galaxy of the Month

  It always feels slightly pointless writing a GOM article for June as it never gets dark here in northern latitudes so rather than going for something faint we will go with the relatively easy challenge of M101.

  M101 was first discovered by Pierre Mechain in March 1781 and has been the subject of some controversy as it has also been suggested that it is the same as M102 as Mechain listed M102 as a duplicate observation of M101. There are suggestions however that M102 was in fact really a different object and modern Messier books seem to randomly choose what object to associate with M102.

  Lord Rosse observing with the 72” at Birr added M101 to his list of nebulae that showed spiral structure and made a drawing of it that compares favourably with modern images.

  When it is dark and at a high altitude M101 is easily visible in binoculars, even my 10x42 Canon IS binoculars will show it, to see detail requires a somewhat larger aperture.

  M101 is such a complex galaxy that it has been given an Arp designation (Arp 26) and two designations in the VV catalogue of interacting systems (394 and 456). It is complex enough that it contains 10 objects within it that have NGC designations (mostly HII regions). The included finder chart shows many of these.

  A recent study suggested that there are upwards of 1264 HII regions in M101. This may be due to gravitational perturbations raised by its companion galaxies (in particular NGC 5474, just over 45’ south of M101, and NGC 5477). In return the gravitational effects on these two caused by M101 is making them form stars at a fast rate.

  M101 is about 23 million light-years away and has a size of perhaps 170,000 light-years, so substantially larger than our own Milky Way, despite recent estimates suggesting our galaxy is much larger than previously thought.

  M101 is part of a small group of galaxies catalogued as LGG 371 which contains perhaps 8-9 other galaxies. The distance of the M101 group is similar to that of the M51 and NGC 5866 groups which suggests they maybe subgroups within a much larger loose group.

  I have found that when observing M101 with my larger telescopes I am caught between using the widefield view which sets the galaxy nicely off in its surroundings and using higher power to tease out the detail. As M101 is a face on spiral then under poor conditions you may only see a haze with a central core but under better conditions the spiral arms and HII regions will leap out at you.

  Note that on the SDSS image the bright blue object on the left at about 9 o’clock is not a plate defect but the giant HII region NGC 5471. Under very steady conditions with a large telescope and high power NGC 5471 may also show structure. It shows up very prominently on the UV images from GALEX. To see multiwavelength images of objects I recommend using the free viewer Aladin.

  

  If finding M101 is not enough of a challenge then perhaps a nice observing project will be to see how many of the M101 group galaxies you can find. These are NGC 5204, NGC 5474, NGC 5477, NGC 5585, UGC 8837 and UGC 9405. Most of them are relatively bright but UGC 9405 is at around 17th magnitude so it may be rather more difficult to see.

  M101 has had one supernova in recent times with sn2011fe which was observed in August 2011 and reached 10th magnitude at its peak. I do remember observing this one although M101 was relatively low at the time using my 15”. Given the amount of star forming activity it is probably a likely source for more supernovae.

  M101 made the OOTW on the DSF forum in 2015 and there are some interesting drawings there made with large telescopes.

  There is interesting web page showing Lord Rosse’s drawings of the spiral nebulae. It is in German but if using Chrome you can ask it to translate the page.

  Owen Brazell - Galaxy Section Director

  I've received an image of M101 captured by Paul Whitmarsh in March this year.

• ACO 2197 Group in Hercules

  May 2018 - Galaxy of the Month

  When we think of galaxy clusters in Hercules people tend to focus on ACO 2151, perhaps better known as the Hercules cluster, and ignore the other two bright(ish) galaxy clusters ACO 2199 and ACO 2197. I have covered ACO 2199 in a very early Galaxy of the Month (GOM) when focusing on its brightest member NGC 6166 so this time we will focus on ACO 2197.

  ACO 2197 is part of the great wall of galaxy clusters which includes the Coma Cluster (ACO 1656), the Leo Cluster (ACO 1367) and the Hercules Cluster (ACO 2151). It lies only a short distance on the sky, about 1.5 degrees, from ACO 2199 and there is evidence of a filament of galaxies linking these two clusters with ACO 2151. ACO 2197 and 2199 along with 2151, 2152, 2147 and 2162 comprise the Hercules Supercluster.

  Classified as a type III cluster on the Bautz-Morgan system ACO 2197 is a fairly irregular cluster containing 11 galaxies catalogued in the NGC so it should perhaps be better known.

  It is covered (as expected) in the Webb Deep-Sky Society Observer's Handbook (WSDSOH) Volume 5 and also on Albert Highe’s web page which includes a detailed list of galaxies in the cluster as well as a finder chart for the central region.

  The brightest three galaxies in the cluster, NGC 6160, NGC 6173 and NGC 6175 were all discovered by William Herschel in 1787. At the same time Herschel also found the fainter galaxies later catalogued as NGC 6146 and NGC 6150. John Herschel also discovered a number of nebulae in the cluster but as these are getting quite faint the other NGC objects were discovered by the Rosse team and Stephan. The Rosse team did discover two other galaxies in this field that did not make it into the NGC.

  ACO 2197 is quite a large cluster in spatial terms covering almost 1.5 degrees in length on the sky. A brief observation of this cluster with Andrew Robertson’s 610mm reflector on a very transparent night suggests that a lot of galaxies may be visible in the field (we had been following galaxies in the ACO 2199 cluster for such a distance I was checking we had not run into the ACO 2197 cluster by mistake).

  As with ACO 2199, ACO 2197 is dominated by a giant cD galaxy, in this case NGC 6173 along with two other giant ellipticals (NGC 6146 and NGC 6160). The cluster is thought to be at a distance of perhaps 126 Mpc. In terms of galaxy numbers ACO 2197 would appear to contain maybe 1500 galaxies or more, so it is quite a large cluster. It may also be interacting with ACO 2199 as the clusters may only be 9.2 Mpc apart in space.

  The cluster appears to form an E-W alignment based on the bright galaxies NGC 6146, NGC 6160 and NGC 6173, a line almost a degree long. As such even with modern wide field eyepieces this cluster is going to take quite a few fields to study. It may however be more tractable than the galaxy fields of Coma. It does seem that in general the galaxies congregate at either end of the cluster around NGC 6146 and NGC 6173.

  

  One of the more interesting galaxies in the group is the double galaxy NGC 6175, which appears to be a spiral and an elliptical almost on top of each other. The pair would appear to be included in the updated VV catalogue as VV 1816, although I am not sure of evidence of interaction. It would be an interesting challenge to see what aperture telescope is needed to split this pair. As always good seeing will be needed as well as good transparency I would think.

  Having said all this it is probably worth noting that the Night Sky Observer's Guide (NSOG) regards the brighter galaxies in this group as challenges for 16/18” telescopes.

  Owen Brazell - Galaxy Section Director

• NGC 4065 Group in Coma Berenices

  April 2018 - Galaxy of the Month

  This group of 9 NGC galaxies in Coma is an extremely confusing field as some of the galaxies seem to have been observed by William Herschel and then later by John Herschel but given the wrong positions. They were then added into the NGC as separate objects. This has led to a great deal of confusion and to various designation issues.

  The main issues seem to surround the galaxies numbered as NGC 4055, NGC 4057 and NGC 4059 discovered by John Herschel. These are probably the same galaxies discovered by his father and catalogued as NGC 4061, NGC 4065 and NGC 4070 respectively.

  The situation was then further complicated by Marth who, when observing with Lassell’s 48” in Malta, found two more galaxies in this group. Unfortunately the positions that Marth gave were very uncertain so it is difficult to ascertain which NGC number belongs to which galaxy of those he discovered.

  And then there is NGC 4069, another of the galaxies discovered by John Herschel but difficult to tie down to an actual galaxy with any certainty. The situation is further complicated by the fact that the designation NGC 4057 is sometimes given to a completely different galaxy.

  The confusion over these galaxy names is amply illustrated by the two finder charts attached, one from Sky Tools that adopts one of the numbering systems and one from Megastar which adopts the other. The mess around the numbering of these objects is discussed in Harold Corwin’s NGC notes.

  NED appears to adopt the primacy of the NGC 4065 system. If we adopt that numbering system then the NGC 4065/4061 pair is also an interacting pair numbered VV 179. Most of the galaxies in the group are ellipticals with the exception of NGC 4072 which is a spiral.

  The whole group is listed in the WBL catalogue of poor galaxy clusters as WBL 374 which is listed as containing 19 galaxies, including the NGC galaxies 4061, 4060, 4065, 4066, 4070, 4072, 4076, 4074, 4086, 4090, 4089, 4091, 4092, 4093, 4095 and 4098. If this is correct the group would contain two sub groups centred around the galaxies NGC 4057 and NGC 4095, separated by perhaps 30’. Unfortunately the designation issues in the second sub group around NGC 4095 are just as messy as in the first.

  NGC 4098 would also appear to be an interacting system and is catalogued as VV 61. It would be interesting to know what power and size of telescope is required to split this system as the SDSS image shows a second galaxy much closer in along with the disturbed spiral arms of the main galaxy. As the separation between the galaxies is only about 10” it is likely to require high power and good seeing.

  The distance to this group is probably of the order of 100 Mpc. The magnitudes of these galaxies suggest that to adequately explore the group, certainly from typical UK skies, will require a telescope of at least 40cm aperture and probably more.

  

  Andrew Robertson when using his 24” telescope drew not only the NGC galaxies in the 4057 subgroup but also managed to pick up one of the UGC ones as well. Unfortunately at the time he did not know about the rest of the group so was not able to get the others.

  Owen Brazell - Galaxy Section Director

• NGC 3090 in Sextants

  March 2018 - Galaxy of the Month

  There have been some comments that recent GOM’s have been too easy as some of the galaxies were bright enough to have been plotted on the Pocket Sky Atlas (PSA) 😊 This month then we go to Sextans and the small galaxy group around NGC 3090.

  The six NGC galaxies in this group were discovered on the 22nd Jan 1865 by Albert Marth using William Lassell’s 48” telescope in Malta. This was one of the last of the large speculum metal mirror telescopes. For further information on Marth’s work with this telescope and his catalogue of nebulae see Alan Dowdell’s article in the Webb QJ 100, or of course Wolfgang’s monumental work on Observing and Cataloguing Nebulae and Clusters.

  The group consists of NGC 3083, 3086, 3090, 3092, 3093 and 3101. It does appear to be a physical grouping and has the galaxy cluster catalogue number WBL 248. The galaxy CGCG 8-18 is also part of this group. As listed in the WBL the group contains 7 galaxies.

  These galaxies will be much more challenging to find as most of them are in the 13-15th magnitude range. As expected this is too faint to appear in most of the classic references such as the Night Sky Observer's Guide (NSOG).

  Most of the galaxies in the group are edge on (or close to it) spirals but NGC 3090 itself as an E4 galaxy, it is also classified as a cD (cluster dominant) galaxy. If the distances published are correct then the group is at a distance of about 108 Mpc, which would give NGC 3090 a diameter of maybe 200,000 lyrs, about twice the size of the Milky Way.

  Recent observations of the group taking into account dwarf galaxies suggest that the total cluster membership maybe nearer 20 galaxies. Many of these surveys however where based on algorithms to find cluster members and hence they are based on statistical surveys, the galaxy group in this case was MZ 03587 from a study done by the 2DFGRS galaxy survey. The group is also known as MKW 1 from a survey of cD galaxies done by Morgan, Keenan and White in 1975. If these studies are right then NGC 3090 is a true poor cluster and it may well be a fossil cluster, the end of the merging process of a group of galaxies.

  Observations of the group may well be hampered by the two 10th mag stars involved with it. It will be interesting to see what size aperture is required to pick up all the NGC galaxies in the group.

  Owen Brazell - Galaxy Section Director

• NGC 3245 in Leo Minor

  February 2018 - Galaxy of the Month

  NGC 3245 in Leo Minor is part of a small group of galaxies catalogued as LGG 197. The group also includes the galaxies NGC 3245A, NGC 3254, NGC 3277 and NGC 3265.

  NGC 3245 itself was first discovered by William Herschel in 1784 and is a mildly active galaxy of a type known as a LINER/HII transition object. NGC 3245 is classified as a lenticular galaxy and observations with the Hubble Space Telescope suggests that it contains a supermassive black hole at the centre. The mass of the black hole is probably going to be of the order of 2 x 10⁸ solar masses.

  NGC 3245 appears to form a physical pair with the superthin edge on galaxy NGC 3245A. It should be noted that the use of a letter on NGC designations normally comes from much later cataloguers, often from those using the POSS plates. In this case I believe the A designation comes from the RNGC catalogue of Sulentic and Tifft. The letter designations were also sometimes assigned in the RC2 catalogue which was published slightly later.

  NGC 3245 itself may not be much of a visual challenge as it is quite bright however its companion NGC3245A I think will be and is probably going to be one for observers with larger scopes of 40cm+ aperture in a good transparent sky. NGC 3245A is also classified as a low surface brightness galaxy. Steve Gottlieb in his NGC notes suggests that with his 17.5” telescope from altitude it was an averted vison object at best.

  It is not clear if the pair are tidally interacting, although GALEX images in the UV suggest there is a lot of star formation going on in NGC 3245A. NGC 3245A is also catalogued as RFGC 1796 in the revised flat galaxy catalogue. It is also listed in Alvin Huey’s Observing Flat Galaxies guide. The distance to the NGC 3245/3245A pair is of the order of 21 Mpc.

  Hubble observations, particularly with the NIC (Near Infrared Camera) seem to show dust features near the nucleus of NGC 3245, which is a little unusual for a S0 galaxy. Chandra also showed that there were X-Rays coming from a small jet from the nucleus.

  The other galaxies in the group are substantial distances away on the sky from NGC 3245, of the order of a degree or more so this is not a tight group of galaxies. The other galaxies in the group, with the exception of NGC 3245A, were also discovered by William Herschel, although not on the same sweeps. NGC 3254 was discovered almost a month earlier than the others.

  As such they should be relatively easy targets for medium aperture telescopes, say 30cm aperture. NGC 3265 may however be a bit more challenging as it is much fainter than the others. NGC 3254 is a nice edge on spiral the others are much less interesting.

  Owen Brazell - Galaxy Section Director

• NGC 3430 in Leo Minor

  January 2018 - Galaxy of the Month

  For the first time in the GOM column we head into the constellation of Leo Minor and the nice group of galaxies around NGC 3430. All of the NGC galaxies in the group (NGC 3430, NGC 3425, NGC 3413, NGC 3395 and NGC 3396) were discovered by William Herschel in 1785.

  The area is also littered with IC objects that were discovered by Bigourdan, although almost none of them are real, he was obviously having a bad night!

  The group is listed as LGG 218 which apparently contains 10 galaxies including the main core around NGC 3430. However, it appears from its radial velocity that NGC 3413 is not part of the physical group, just a line of sight addition.

  NGC 3395/6 are also known as Arp 270 and it maybe that Bigourdan saw a knot in the spiral arm of NGC 3395 part of this galaxy pair when he reported the object that became IC 2605. This pair were also noted in the VV catalogue of interacting systems that preceded Arp’s work. Arp 270 has also featured in the DSF OOTW column.

  NGC 3430 itself is classified as a Wolf-Rayet (WR) galaxy, a relatively rare type of galaxy undergoing a strong burst of star formation and showing emission lines in its spectra. The WR phenomena in galaxies are normally triggered by interactions between galaxies and it is thought that NGC 3430 is interacting with NGC 3424 and indeed deep images and radio observations suggest that both NGC 3430 and NGC 3424 do show signs of tidal interaction.

  NGC 3430 was also one of the galaxies that the Rosse team at Birr thought were spiral in nature, and it appears that they were correct in that call in this case. With the exception of NGC 3413 which is a lenticular galaxy all of the others in the field are spiral in nature.

  The group is probably of the order of 90 million light years away, although I have seen distances as close as 76 million light years quoted.

  Arp 270 is a merging galaxy system, probably in the early stages of the merger and there is a lot of star formation going on. There is a sixth NGC galaxy which is also part of the LGG 218 group in NGC 3442 but this is almost a degree north of the main core around NGC 3430.

  The main galaxies are bright enough to be seen in medium aperture telescopes, of the order of 30cm, and the group around NGC 3430 is a nice triple system when using high power. All five galaxies may appear on the same field when using a modern hyperwide eyepiece with a medium power of say 180x.

  Also in the same area is IC 2604, a 14th magnitude galaxy that was discovered by Javelle in 1896. It is also thought to be part of the group and will be a challenge for owners of larger telescopes. So overall an interesting group which appears to have two independent interaction events going on in it.

  Owen Brazell - Galaxy Section Director