Galaxy of the Month Archive 2021

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

• NGC 1723 in Eridanus

  December 2021 - Galaxy of the Month

  NGC 1723, along with NGC 1721, NGC 1725 and NGC 1728, forms a nice quartet of galaxies in Eridanus. Perhaps surprisingly they were not found by William Herschel. NGC 1723 was discovered by Tempel using a 11” refractor in 1882 and the other trio by Barnard in 1885 using the 6” refractor at Vanderbuilt university, and independently by Lewis Swift using a 16” refractor a month later.

  Although the group only just rises above one air mass from the southern UK (it is just below Rigel) it should not be that difficult to observe, although to be fair the discoverers all regarded the objects as quite faint.

  The NGC 1721, NGC 1725 and NGC 1728 trio are also classified as VV 699 in the Vorontsov-Velyaminov interacting galaxy catalogue. Interestingly though whilst NGC 1723, NGC 1724 and NGC 1728 have similar redshifts NGC 1721 seems to have a much higher redshift. The distances to the first 3 would be around 55Mpc whilst, if the redshift velocity is a true distance indicator, NGC 1721 is at around 66 Mpc. I wonder then if NGC 1721 is purely a line-of-sight galaxy and the others are an interacting triplet. However, given that NGC 1721, NGC 1725 and NGC 1728 seem to be interacting the redshift for NCG 1721 may just reflect peculiar motions within the group rather than a true distance. The discrepancy would not be out of the range for intra group movements. Unfortunately, there are no redshift independent distance measurements to the group.

  NGC 1723 is sometimes referred to as part of this group, although it may be unrelated to the other three galaxies it is an odd galaxy with its spiral arms coming off a ring and a prominent bar. The ends of the spiral arms show some signs of distortions, although it is not clear what galaxy NGC 1723 maybe interacting with. There are a number of other faint galaxies nearby. NGC 1721 is also a spiral galaxy and appears to have signs of an interaction given the way its outer spiral arms are behaving. Neither NGC 1725 or NGC 1728 show much signs of an interaction.

  All the galaxies in the group are spirals with the possible exception of NGC 1725 which is classified as an S0, a lenticular. The NGC 1721 trio has also had the designation KTS28 in the catalogue of isolated southern triplets by Karachentseva, although of course if NGC 1723 is part of the group then this designation would be somewhat misleading. Perhaps surprisingly there has not been that much research done on the group.

  

  The group is included in the Interstellarum Field guide where it suggests they are targets for 8” telescopes but as usual I suspect that this is optimistic unless you are observing from 2000m in the Alps. The Night Sky Observer's Guide (NSOG) Vol 1 suggests the group are more likely to be challenges for 40-45cm telescopes and I suspect from the UK that this maybe more likely. The group is sufficiently tight that all the main galaxies will appear in the field of a medium to high power modern hyperwide field eyepiece. Given their altitude I suspect that trying to observe them within an hour of meridian transit and a good southern horizon may be needed.

  Owen Brazell - Galaxy Section Director

• Abell 347 in Andromeda

  November 2021 - Galaxy of the Month

  Near to the well-known edge on galaxy NGC 891 lies the small group of galaxies known as Abell 347. The cluster is relatively poor in Abell terms but contains 7 galaxies: NGC 906, NGC 909, NGC 910, NGC 911, NGC 912, NGC 914 and NGC 923.

  The cluster is part of the Perseus-Pisces Supercluster, which also includes the clusters Abell 262 and Abell 426. The Perseus-Pisces super cluster is thought to be the most massive object within 300 million light-years. More information on the filament can be found at The Atlas of the Universe.

  NGC 898 and NGC 910 were discovered by William Herschel in 1786. NGC 906, NGC 909, NGC 911 and NGC 914 were found by Stephan in 1878, and Dreyer found NGC 923 in 1874. NGC 898 is sometimes included as part of the cluster but appears to lie outside the core region. There was some thought that the active galaxy 3C66A was part of the cluster but it is now thought to lie well behind in another cluster.

  Abell 347 probably lies at a distance of about 240 million light-years, and is classified as a richness class 0 and a distance class 1 in the Abell classification scheme. Here richness goes from 0 (least rich) to 5 (most rich) in terms of galaxy numbers. It has a putative Rood-Shastry class of I.

  The Brightest Cluster Galaxy (BCG) is probably the large elliptical NGC 910. It has also been classified as a cD galaxy. However most of the brighter galaxies in Abell 347 appear to be spirals which suggests that this is a young group and the expected mergers have not yet taken place. Perhaps surprisingly there does not seem to have been much research done on this cluster.

  Although some sources list over 57 galaxies in the cluster the Webb Deep-Sky Society Observer's Handbook (WSDSOH) Volume 5 lists 20 that may be visible in medium large instruments under good skies, There is a nice diagram as well as observing reports on the clusters in the Perseus-Pisces filament at Adventures in Deep Space.

  Observationally the group is fairly compact and most of the main galaxies, with the exception of NGC 898 and NGC 914, will fit in a single medium power (270x) field using a modern hyperwide eyepiece. My suggestion, given the faintness of these galaxies, is to use the highest power you can to get the contrast up. My observations under poor skies using a 55cm showed most of the main galaxies, but I did not pick up any of the MCG galaxies in the field.

  There is an article on the Skyhound website on observing this group. Unfortunately most images of the cluster are usually framed to fit in NGC 891 so the area of interest is rather small. I suspect this group has been overlooked because its proximity to NGC 891.

  My apologies for the brevity of the material in this piece but I have been suffering from Covid whilst writing it.

  Owen Brazell - Galaxy Section Director

• NGC 877 in Aries

  October 2021 - Galaxy of the Month

  NGC 877 is part of a small group of galaxies in Aries that includes NGC 870, NGC 871 and NGC 876. NGC 871 and NGC 877 were both discovered by William Herschel in October 1784 and R.J. Mitchell using Lord Rosse’s 72” found the other two in 1854.

  NGC 877 and NGC 876 lie at the same distance from us, approximately 160 million light-years. NGC 877 appears to be interacting, probably with NGC 876. NGC 877 is the brightest galaxy in the LGG 53 group, an 8 galaxy group, which appears to include NGC 871 as well, but not NGC 870, which is interesting as NASA/IPAC Extragalactic Database (NED) describes NGC 871 as in a non-interacting pair with the compact elliptical galaxy NGC 870. The redshift of NGC 870 however suggests that it is a long way behind NGC 871. The group is also sometimes known as the NGC 877 group.

  NGC 877 itself is classified as an intermediate spiral galaxy but also seems to be classified as a LIRG (Luminous Infrared galaxy) so one assumes there is quite a lot of star forming activity going on, indeed images in the UV from the GALEX satellite show numerous large areas of star formation going on in its spiral arms. Conversely NGC 876 shows very little activity in the UV. There appear to be some faint plumes coming off NGC 877. NGC 871 also appears very bright in the UV. It too is a spiral galaxy.

  A low surface brightness bridge appears to connect NGC 877 and 876 which would confirm the interaction theory. NGC 876 is an edge on spiral with a central bulge and a distinctive dust lane, not unlike the one in NGC 891. Hubble has imaged both NGC 877 and 876 with the WPC 3 but only in the near IR and I have seen no processed images from this.

  The group also has an extensive neutral hydrogen (HI) envelope, which suggests the group is gas rich. There is also an interesting gas cloud in the system which may be a tidally formed galaxy, although this appears to be a radio only object. NGC 870 maybe one of the most distant galaxies in the NGC.

  The Night Sky Observer's Guide (NSOG) Volume 1 suggests the two brighter galaxies NGC 877 and NGC 871 should be in range of a 25cm telescope but the other two are probably going to require 45cm, at least from UK skies. A UK observation of NGC 877 suggests however that it is tough even with 40cm. The group is quite tight so will fit in the field of a medium to high power eyepiece. Indeed it is probably going to require a high power eyepiece to darken the field enough to catch the fainter pair.

  It should be noted that Steve Gottlieb found both NGC 870 and NGC 876 very difficult even with a 18”. Owners of large telescopes may also be able to catch the galaxy UGC 1781 between the two pairs, however this is a face on spiral and at magnitude 14 is going to be a hard catch except among the best skies, at least for visual observers. I have seen no recorded observations of it.

  NGC 877 was one of the galaxies reported by the Rosse team as spiral in nature. It also makes the Herschel 3 list and is listed, although not described, in Burnham's Celestial Handbook (BCH) Vol 1. There is a nice image of the group by Adam Block at Caelum Observatory.

  Owen Brazell - Galaxy Section Director

• NGC 7463 in Pegasus

  September 2021 - Galaxy of the Month

  Our target this month is the tight triplet of galaxies around NGC 7463 in Pegasus. NGC 7643 itself was discovered by William Herschel in 1784 along with the other brightish galaxy in the group, NGC 7465. The other galaxy in the triplet, NGC 7464, was discovered by d’Arrest in 1864, although it was independently rediscovered by Marth and Vogel later that year.

  The WBL has it as part of a small galaxy group listed as WBL 695 which includes the 3 NGC galaxies and UGC 12321. The faint edge on spiral UGC 12313 nearby is not listed as part of the group, however HI observations suggest that it may be connected with the others.

  NGC 7463 itself appears to be a barred spiral galaxy with the outer spiral arms distorted by interactions, possibly with NGC 7464. NGC 7464 is itself an interesting system as it is classified as E1pec, although its colours are very blue and it shows emission lines. There are other morphological classifications which suggest it maybe an irregular galaxy however. The NGC 7463/7464 group is also known as Holmberg 802.

  The third galaxy in the trio, NGC 7465, is also classified as a distorted form of a barred spiral. The nucleus of NGC 7465 seems to be a LINER, a mild form of AGN and the galaxy contains a lot of dust. It has also been classified as a Seyfert 2 type system. It appears to have a ring of star formation, or a shell of material which may come from interactions within the system or from a merger in the past. It could perhaps also be a polar ring galaxy. The core of the NGC 7465 also appears to have some intense star forming going on.

  The main interactions in the group appear to be currently between NGC 7464 and NGC 7465. Interestingly the Lyons Groups of Galaxies (LGG) has NGC 7465 and 7464 as part of the NGC 7448 group as LGG 469. NGC 7463 is not part of that group.

  The group is fairly small and faint and thus it is of interest that the Night Sky Observer's Guide (NSOG) Vol 1 suggests it as a target for 12/14 inch telescopes. It does not appear in Luginbuhl and Skiff (L&S). Steve Gottlieb suggests that even in a 18” telescope NGC 7464 was faint. The group is very tight and as such is probably going to require high magnification in order to be able to split all the components, in the range I would think of 250-350x.

  Owners of large telescopes may also be able to pick up the two UGC galaxies associated with the core trio, although I expect finding these may require the most transparent nights, although Steve Gottlieb reports that they are faint even in Texas skies with a 48”.

  Owen Brazell - Galaxy Section Director

• NGC 6661 in Hercules

  August 2021 - Galaxy of the Month

  With the return of dark skies in August we can move to some more challenging targets for the GOM. This month I have chosen the faintish pair of galaxies in eastern Hercules, NGC 6661 and NGC 6658.

  Both these galaxies were initially discovered by Albert Marth in 1864 using William Lassell’s 48 speculum metal telescope in Malta. However confusion was added to the area when Lewis Swift using his 16” refractor reported another nebula in the area in 1885 which was recorded as NGC 6660. It was later shown that this object was identical with Marth’s object NGC 6661 so it can have both NGC numbers. Edouard Stephan also independently rediscovered it in 1871. The correction was noted in the notes accompanying the IC1 in 1895 so it is a long-known issue.

  Both of these galaxies are classified as S0-a, so they are lenticular galaxies. NGC 6658 appears to be more like an edge on spiral but shows no spiral arms or dust features. It does however appear to have quite a bright nucleus. NGC 6661 is in range of 25cm from the UK but shows only as a very faint object.

  NGC 6658 and NGC 6661 are suggested to be a non-interacting pair according to the Second Reference Catalogue of Bright Galaxies (RC2). The distance to NGC 6661 is suggested to be about 42Mpc. There is some doubt however about them being a physical pair as NGC 6658 is listed as being part of the galaxy group LGG 421 and NGC 6661 is not. The other NGC galaxies associated with LGG 421 are NGC 6641 and NGC 6669. This would fit with their redshifts being vastly different with NGC 6661 being the further away (or moving much faster) so the pair appear to be just a line-of-sight effect. Interestingly though, as lenticular galaxies you would expect to see them as part of a group, or at the very least a fossil group if the understanding of how lenticular galaxies form is correct. NGC 6658 appears to be the brightest galaxy in LGG 421 but interestingly shows very little radio emission.

  Perhaps not unsurprisingly the galaxy pair is not included in the Night Sky Observer's Guide (NSOG). As the pair is quite tight it should fit within a high-power eyepiece field of view, and indeed because of the faintness of the pair you are probably going to need to use medium to high power in order to boost the contrast enough to see the them. Although as noted a 25cm will just about pick up NGC 6661 I suspect that probably 40-50cm will be needed to see NGC 6658 given its discovery history, although again there are reports of it being seen on the edge with a 25cm telescope from UK skies.

  Owen Brazell - Galaxy Section Director

• NGC 6487 in Hercules

  July 2021 - Galaxy of the Month

  Following on from the June GOM, July is also a poor month for galaxy observing from the UK with summer twilight in full swing. My choice this month is the galaxy NGC 6487 in Hercules as it will hopefully be in the darker part of the sky.

  Both NGC 6487 and its fainter companion NGC 6486 were discovered by Edouard Stephan using the 31” (80cm) silver on glass reflector at Marseilles. NGC 6487 was discovered in 1871 and NGC 6486 6 years later in 1877.

  I find it interesting coming from the UK that the 31” was mounted outside without any form of cover, building wise anyway. Just shows the quality of the weather in Marseilles. This was one of the first large silver on glass reflectors made by Foucault.

  Both the galaxies are elliptical with the classifications just showing a generic E so they have not had more detailed classifications done on them. NGC 6487 would appear to be a head-tail radio source which suggests an AGN of some form, at least in the past. The two galaxies appear to be part of the poor galaxy group WBL 648. The group contains only three galaxies and includes the face on spiral UGC 11017 as part of the trio with NGC 6486 and 6487. NGC 6487 does show a bright core in the UV which suggests some form of activity. UGC 11017 does show a lot of activity in the UV suggesting lots of star formation going on. Otherwise, perhaps not unsurprisingly, there is not much research done on these galaxies. So many galaxies so little time 😊 The group is at a distance of about 120 Mpc so quite a distance out.

  All the galaxies in the group are very close together so using a high-power eyepiece, perhaps of the order of 340x if your telescope will take it, will help when trying to split it. I suspect that NGC 6487 may not be that hard to see but at 15th magnitude NGC 6486 is going to be much more difficult to see, especially in the summer twilight. The other galaxy in the trio, UGC 11017, is nearer to 16th magnitude and close to face on so it is going to be a challenge I think for all but the largest telescopes, and even then only the core will be seen. Perhaps not unsurprisingly the pair does not make the Night Sky Observer's Guide (NSOG) or other standard observing guides.

  Owen Brazell - Galaxy Section Director

• NGC 5899 in Boötes

  June 2021 - Galaxy of the Month

  It seems in some ways pointless to do a galaxy of the month for June and July from here in the UK as it never really gets dark enough to chase galaxies down, unless they are really bright. However, for the sake of completeness I have chosen the bright spiral galaxy NGC 5899 in Boötes for this month’s challenge.

  NGC 5899 appears to be in a non-interacting pair with the much fainter NGC 5900 according to the RC2, however recent deep images of the pair suggest there are tidal tails coming off NGC 5900 and the dust lane in NGC 5900 also appears warped which suggests that a gravitational interaction is taking place between the pair.

  Both of these galaxies were discovered by William Herschel in 1787, although not in the same sweep. Mitchell observing with Lord Rosse’s 72” at Birr believed he found another two nebulae near NGC 5900 although the one catalogued as NGC 5901 turned out to be just a star. The field also contains the much fainter and unrelated galaxies NGC 5893, NGC 5895 and NGC 5896.

  If the distance measurements are correct NGC 5899 is about 46Mpc away. NGC 5899 appears to be a spiral galaxy seen at a highly inclined angle and has been given the rather complex morphological classification of SAB(rs)c which suggests it has a ring from which the spiral arms start. NGC 5900 is also a spiral but in this case seen almost edge on with a strong dust lane. NGC 5899 has also been classified as a Type 2 Seyfert galaxy which suggests it has an AGN. The UV images from GALEX show bright star forming regions in its spiral arms. The tidal tail in NGC 5900 also seems to show some UV emission.

  Visually observing the field is complicated by the existence of the 6th magnitude star SAO 45445 close to the galaxies and a high-power eyepiece maybe needed to keep it out of the field when observing the galaxies. UK observations suggest that NGC 5899 can be seen faintly with a 25cm scope, although the same observer did not record an observation of NGC 5900 which suggests it is fainter. If you find NGC 5899 and NGC 5900 too easy then try for the fainter trio around NGC 5893 the other side of the star. Although NGC 5899 does not make the Herschel 400 list it does make the H400 II list. Steve Gottlieb’s observations of the field (along with all other NGC objects) can be found on his website.

  Owen Brazell - Galaxy Section Director

• NGC 5566 in Virgo

  May 2021 - Galaxy of the Month

  This month’s GOM is the triple system associated with NGC 5566, also known as Arp 286. The galaxies lie in the far east of Virgo. The system is composed of the galaxies NGC 5566, 5560 and 5569.

  NGC 5560 and NGC 5566 were discovered by William Herschel in 1786 but the much fainter galaxy NGC 5569 had to wait until 1849 when it was discovered by Johnstone Stoney using the 72” at Birr. Dreyer in 1878 also noted the faint galaxy now catalogued as CGCG 047-019 and sketched it while he was examining the NGC 5566 field but did not manage to get an accurate position for it so it never made it into the NGC.

  The three NGC galaxies appear to form a physical triplet. All three galaxies appear to be spirals. Arp classified NGC 5566 in his group of double galaxies, infall and attraction, connection not visible. The triplet is also included in the WBL catalogue as number 501 and in the LGG as number 379. The former only includes the triplet but the LGG catalogue has 6 galaxies in LGG 379 and includes the triplet composing of NGC 5574, NGC 5576 and NGC 5577 about 41’ south as part of the group.

  The NGC 5566 group appears to be interacting from the distortions in the spiral arms of NGC 5560 and also all three galaxies have strong UV emission as noted by the GALEX satellite, which suggests lots of star formation going on. NGC 5566 is particularly interesting as it appears to have a strong ring from which the spiral arms appear to radiate rather than the normal bar or core, giving rise to its morphological classification of SAB(r)ab. Deep images also suggest that NGC 5566 has tidal plumes pulled out as part of the interaction. The spiral arms of NGC 5560 are also strongly distorted. NGC 5566 appears to be a LINER type AGN, perhaps not surprising as the interactions are likely to be feeding the black hole at its centre.

  The group is about 85 million years or so away. The suggestion is that if the group is at this distance then NGC 5566 is about 150 million light-years across so much larger than our Milky Way and would be one of the largest galaxies in Virgo. There is a superb amateur image of this group.

  Visually the group should contain challenges for all size telescopes. NGC 5566 should be visible in 20cm telescopes but to see NGC 5569 is probably going to require 45cm+. Luginbuhl and Skiff (L&S) suggests that 15cm should be enough to see NGC 5566 but I suspect this was form a high altitude site. I am guessing that since the Rosse team saw CGCG 047-019 then it should visible in 50cm+ so a nice challenge for large telescope observers. The triplet is compact enough that it should fit in a medium power (270x) field with a hyperwide field eyepiece. CGCG 047-019 (also known as PGC 51269) will also be in the same field. Of the NGC galaxies NGC 5690 is going to be the hardest to find as it is a face on low surface brightness object and probably only the core will be seen. NGC 5566 is part of the H400 II listing from the Astronomical League.

  Owen Brazell - Galaxy Section Director

• NGC 3637 in Crater

  April 2021 - Galaxy of the Month

  For this month’s challenge we dip down into the constellation of Crater. Unfortunately, this means our targets will not rise that high as seen from the southern UK.

  NGC 3636 and 3637 were both discovered by William Herschel in 1786 and then independently by Andrew Common in 1880. Although Common is perhaps best known now for his photographic work, the NGC objects he discovered were all found visually using his 36” reflector from Ealing near London. This is the same telescope that went on to become the Crossley reflector at Lick.

  The two galaxies appear to form a physical but non-interacting pair. NGC 3636 is classified as an E0 and NGC 3637 as a lenticular but of a complex form with a strong bar and a ring around it. This leads to the rather complex morphological classification of (R)SB0(r). The pair are associated with a group of galaxies associated with NGC 3672 known as LGG 235, which contains only these three galaxies. The group is fairly widely spread on the sky with NGC 3672 being over a degree away from the other two. As perhaps expected from their classifications these galaxies consist of old stars with no signs of star formation going on. Perhaps surprisingly not much research has been done on this pair and most of what has been done has been on the structure of NGC 3637. The group lies at a distance of perhaps 21Mpc from us. The pair merits a couple of pages in the Annals of the Deep Sky Volume 7.

  Observationally this group will be a challenge not only because of the low altitude at which it culminates but also because of the presence of the presence of the bright 7th magnitude star HD 98591 between them. Both galaxies have bright cores and it may well be this is all that can be seen of them.

  I note that in the glare of the bright star there is another galaxy that does not appear in any of the other main visual catalogues, probably because on the plates they were compiled from it was overwhelmed by the glare from the star. The galaxy is only listed in surveys in the IR from the WISE satellite and also in the UV from GALEX. It will be interesting to see if it is visible in larger telescopes but I suspect the glare of the star will be too much.

  My suspicion is that high power is going to be needed to work on this group so the unusual combination, for the UK anyway, of a clear transparent night with good seeing maybe required for this pair. The pair does make the Night Sky Observer's Guide (NSOG) Vol.2 which suggests they are a target for 12/14” scopes. Both galaxies make the Astronomical Leagues Herschel II list.

  Owen Brazell - Galaxy Section Director

• NGC 2872 in Leo

  March 2021 - Galaxy of the Month

  The small trio of galaxies around NGC 2872 in Leo, also known as VV 1284 and Arp 307, where it is included as part of the Double Galaxies class.

  The galaxies in the group were discovered by a number of different observers with the brightest pair of galaxies (NGC 2872 and NGC 2874) being discovered by William Herschel in 1784. It took Mitchell using the 72” at Birr to find NGC 2873 in 1857 however. Whilst observing the group he also found a number of other objects that he believed to be nebulae and one of these was later catalogued as NGC 2871. Unfortunately, this later turned out to be just a star. Another case one suspects of poor seeing making stars look nebulous. The Rosse team also thought they had found another nebula in the area, which it turns was actually a knot in one of the spiral arms of NGC 2874, however it got its own NGC number as 2875.

  NGC 2872 is an elliptical galaxy and possibly an AGN as it has a bright UV core and radio lobes. The group is also known as Holmberg 130. NGC 2872 is interacting with NGC 2874. NGC 2873 is probably only optically associated as it appears to be at a different redshift, otherwise not much seems to be known about it. The Galaxy Zoo project classifies NGC 2873 as a red spiral, one of the new types of galaxy classification to come out of that project. Intriguingly NGC 2874 also seem to be classified as heading that way although the GALEX images show a lot of star formation happening in its arms which is slightly odd if that is the case. Very deep images of NGC 2874 show signs of tidal streamers, possibly from an interaction or merger with a dwarf galaxy. The distance to the group is probably of the order of 110 million light-years (33Mpc). Arp lists the group under his classification of Double Galaxies.

  Hubble does seem to have observed the group a long time ago and no colour images seem to have been made however there is a black and white image.

  

  Interestingly the DSS image of the group shows NGC 2872 as quite a small elliptical. However deeper images from newer surveys (SDSS, PanSTARRS) show it has a bright core and a very much larger extended halo and here it is classified as an E2. Perhaps surprisingly as an Arp galaxy not much research appears to be available on this system.

  The group is very tight so observing this will require high power and steady seeing to split the galaxies. NGC 2872 and NGC 2874 should be quite easy but finding NGC 2873 may be a challenge for larger telescopes. Steven Gottlieb found it very faint even with a 24” and requiring averted vision to hold. Interestingly the group does not make the Night Sky Observer's Guide (NSOG), which is perhaps surprising as it has an Arp designation, it is perhaps time to remember that the core NSOG series is now pretty old and telescope sizes in particular have moved on. It does make Luginbuhl and Skiff (L&S) however where the suggestion is that from high altitude the two brighter galaxies are visible in 15cm but a 30cm shows them better. Interestingly they suggest that NGC 2873 should be visible in 30cm which does not tie in with Steve G’s observation above. I note that with a 25cm from the UK the group was not regarded as particularly impressive.

  Owen Brazell - Galaxy Section Director

• NGC 2389 Group in Gemini

  February 2021 - Galaxy of the Month

  Although rather late in the season this small group of galaxies in Gemini is still high in the sky at a reasonable hour.

  The group, consisting of the galaxies NGC 2389, NGC 2388 and NGC 2385, was all discovered by William Herschel. He first found NGC 2389 itself in 1788 and then the other two galaxies in 1793, perhaps by this time he had moved to front view mode and gained an extra magnitude or so in what he could see.

  There are a number of non-existent NGC objects in the area in NGC 2386, NGC 2390 and NGC 2391. These are all stars that were discovered by the Rosse team at Birr and thought to be nebulae but which later turned out to be stars. One suspects that they were fooled on a night of poor seeing/transparency when the stars looked nebulous, an issue that still plagues visual observers in the UK.

  The group is also catalogued as WBL 142 which contains just these three galaxies. The group would appear to lie about 200 million light-years from us. NGC 2388 itself is an interesting type of galaxy known as a Luminous Infra-red Galaxy (LIRG). These are normally galaxies where there is a lot of star formation going on that is hidden by dust, which is then heated by the starlight to glow in the Infra-Red. They are also usually very red in colour. All the galaxies in the group are classified as spirals but the type of NGC 2388 is unknown. All the galaxies in the group appear disturbed but there are no obvious signs of interaction, such as tidal tails etc..

  NGC 2389 is an almost face on spiral with a relatively bright nucleus and signs of a bar which fits with its SAB(rs)c classification in the rather involved de Vaucouleurs system. For some reason NED also lists this galaxy as NGC 2388E, although this may have come from the RNGC by Sulentic and Tifft. NGC 2389 is a well-developed spiral with lots of young blue stars whilst both of the others are somewhat reddish. The UV GALEX image backs this up with NGC 2389 itself showing lots of star formation and the other two being practically invisible. NGC 2385 appears close to edge on with a well-developed dark dust lane. The suggestion is that NGC 2389 and 2388 form a pair with NGC 2385 a more distant part of the group.

  The Night Sky Observer's Guide (NSOG) Vol 1 recommends the group as a target for 40-45cm telescopes but also suggests that the small faint edge on galaxy UGC 3879 nearby should also be visible. I suspect that from UK skies probably 45-50cm may be needed to see all the galaxies in the group. All four should be in the same FOV with a medium power widefield eyepiece. I suspect however that UGC 3879 is going to be a challenge for all but the best nights.

  Also in the same medium power field is the faint spiral NGC 2393, a Stephan discovery, so there are a lot of objects to go for in this field. There is also a nice pair of galaxies nearby associated with NGC 2275 which has been covered before in the GOM series.

  Owen Brazell - Galaxy Section Director

• NGC 2805 in Ursa Major

  January 2021 - Galaxy of the Month

  The small group of galaxies around NGC 2805 has an interesting discovery history. Three of them, NGC 2805, NGC 2814 and NGC 2820 were discovered by William Herschel in 1791. The last galaxy in the group is listed as either NGC 2820A or IC 2458. However, it appears that Bigourdan, who discovered IC 2458 in 1899, really meant to apply that designation to a knot in NGC 2820 so the galaxy is not the IC object. This small galaxy is also known as Markarian 108. John Herschel also managed to add to the confusion in the area as he recorded another nebula that became NGC 2816. NGC 2816 is however just another observation of NGC 2820 so that number should be retired.

  The group also became known as Holmberg 124 after Erik Holmberg’s catalogue of double and multiple galaxies in 1937 that he found from early photographic plates, an effort that was corrupted by poor images and led to a number of false identifications. The group is also catalogued as LGG 173 which adds NGC 2880 to the group to make a 5 galaxy system, which is slightly odd as NGC 2880 is almost 2 degrees away from the others.

  The group is classified as a poor galaxy group and consists of mostly late type spirals. The distance to the core of the group is around 90 million light-years or so. GALEX images in the UV show a lot of active star formation going on which suggest that the group has interacted in the recent past to stir up the star formation. The group does not show up so well in the IR WISE images. NGC 2814 in particular shows a number of knots, a bit like M82, and almost looks like two galaxies in collision. NGC 2820A also appears very disturbed.

  

  NGC 2805 is a face on spiral with well-defined arms in the central part but somewhat asymmetric arms further out. On the Sloan Digital Sky Survey (SDSS) image there is a diffuse patch that I initially thought was another dwarf galaxy in the system but is more likely to be an artifact from the bright star in the field as it does not appear on other survey images. There is a nice image at ManTrapSkies.com. NGC 2805 was also host to the recent supernova 2019hsw. Interestingly although the galaxies around NGC 2820 show signs of interacting with each other from their radio emission and there is a tidal bridge between all of them, there is no tie up with NGC 2805. It also appears that there may be a tidal dwarf galaxy created in the streams from NGC 2820 to the NE of it.

  The group is fairly compact and will fit in the field of a medium power (say 260x) hyperwide eyepiece. None of the galaxies in the group make the Night Sky Observer's Guide (NSOG) which is perhaps rather surprising. They do however make Luginbuhl and Skiff (L&S) where they suggest that a 30cm telescope is required to see much. NGC 2805 is a fairly low SB galaxy so perhaps only the small diffuse nucleus will be seen. I suspect the use of high power may help on the smaller galaxies to see if any detail can be seen. The NGC 2820 triplet does make the Interstellarum Field Guide, although not NGC 2805. NGC 2805 does make the H400 II list but the others in the group don’t.

  Owen Brazell - Galaxy Section Director