Galaxy of the Month Archive 2019

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

• NGC 1888 and Arp 123 in Lepus

  December 2019 - Galaxy of the Month

  The galaxy pair NGC1888/1889 in Lepus was first discovered by William Herschel in 1785, although he only saw one of the pair, NGC 1888. It took Bindon Stoney using Lord Rosse's 72" in 1851 to discover the smaller galaxy in the pair which became NGC 1889.

  Arp catalogued the pair as Arp 123 in his group of "Ellipticals close to and perturbing spirals". NGC 1888 does look as it is being distorted by an encounter with extended spiral arms. The galaxy does have a spiral arm on the opposite side to NGC 1889 which contains lots of young blue stars. Vorontsov-Velyaminov also included it in his extended catalogue of interacting galaxies as VV 1138. The pair also hosted the Type Ia supernova SN 2018yu.

  The galaxies lie at a distance of perhaps 110 million light years from us.

  Close by and in the same high power field is the edge on galaxy MCG-2-14-15, also known as RFGC 973, which at magnitude 14.5 should be visible in larger telescopes. For those with very large telescopes there is a third edge on galaxy called LEDA 147414 (PGC 147414), but at mag 16.5 this is likely to require very large telescopes from high dark sites to find.

  Unfortunately for UK observers Arp 123 never rises that high, barely reaching the 1 airmass line at 30 degrees. Nevertheless it was visible in my 15” telescope and in an 18” at the October 2019 Haw Wood star party in Suffolk at the high altitude of maybe 70m. The MCG galaxy was not seen but the night was not the most transparent. The group did make the DeepSkyForum (DSF) Object of the Week in 2012.

  NGC 1888 is classified as SB(s)c pec and NGC 1889 as cD pec. Arp gave them different classifications as Sc and E0. The pair are almost certainly in the early throws of a merger. MCG -2-14-15 is well in the background and not associated with the main pair.

  Perhaps surprisingly given this is an Arp pair there is not much in the literature on them. The pair makes both the Night Sky Observer's Guide (NSOG) Volume 1 and the Webb Society Deep-Sky Observer's Handbook (WSDSOH) Volume 4, which suggests that a 16” is good whereas the NSOG suggests that a 30cm telescope will show the pair. Both suggest high power is needed to split them.

  Owen Brazell - Galaxy Section Director

• NGC 7436 in Pegasus

  November 2019 - Galaxy of the Month

  This small tight group of galaxies in Pegasus has an interesting discovery history. The brightest galaxy NGC 7436 was discovered by William Herschel in December 1784. However he was not able to resolve the other members of the group and it took Mitchell using the 72” at Birr to find NGC 7433 and NGC 7435 in 1855 and then Bigourdan added the last NGC member of the group (NGC 7431) in 1886.

  The group are also listed as VV 84 in the Voronstov-Velyaminov catalogue of interacting galaxies where he included it in his group of triples with a tight pair, although the group did not get the attention of Arp.

  Dreyer did note another galaxy in the group in 1875 but was not confident enough in his sighting as it was a bad night to list it. This may be the faint galaxy MCG +4-54-7.

  Unfortunately there is some confusion about the NGC designations in this group with the nomenclatures NGC 7436A and B being used for the central galaxy and not necessarily for the same objects.

  Mitchell and Dreyer did provide drawings of the field however which helps in trying to establish what galaxies they saw. The associated chart and image below will show how different galaxies are assigned different numbers.

  

  The group also exists as part of WBL 692, which appears to consist of just the galaxies catalogued in the NGC. The group, also known as Holmberg 800, lies on the outskirts of the galaxy cluster Abell 2153 and is at about 340 million light-years distant from us.

  NGC 7436 itself appears to be an elliptical galaxy with a large outer halo, suggestive of it snacking on other galaxies in the past. That fuzziness makes it difficult to decide if the little galaxy next to it lies in front or behind NGC 7436. NGC 7435 shows signs of an interaction with its distorted spiral arms although it is probably not with NGC 7436 as its recession velocity suggests that it lies behind it. It may be that NGC 7436 is only marginally part of the group of galaxies that we see. There are a number of other faint galaxies in the field including UGC 12274.

  The compactness of the group suggests that to get much out of this will require a night of steady seeing and high power. Observations from Andrew Robertson using a 24” and Mike Wood using a 15” Obsession with an EAA system are included below. Also see Steve Gottlieb’s observations with a 48” dobsonian on his website.

  

  

  The group is also included in Alvin Huey’s selected small galaxy groups atlas and his VV atlas Part 1.

  Owen Brazell - Galaxy Section Director

• NGC 7778 in Pisces

  October 2019 - Galaxy of the Month

  My thanks to Mark Stuart for recommending this rather nice group of galaxies in Pisces. Three of these galaxies, NGC 7778, NGC 7779 and NGC 7782 were discovered by William Herschel in November 1784 and the fourth galaxy NGC 7781 was discovered by his son, John, in 1830 whilst reobserving his father’s objects. Also in this field, but very much fainter is the edge on galaxy, RFGC 4209.

  All of the NGC galaxies are included as a group WBL 727 which contains just the four NGC galaxies. The group is often called the NGC 7782 group after its brightest member. It also seems to be classified as cluster Zwicky 2350.6+0758.

  NGC 7778 and NGC 7779 are regarded as a physical pair, despite this they do not seem to show any signs of gravitational interaction. NGC 7778 is an elliptical whereas NGC 7779 appears to be a face on spiral with a very bright core, although it has also been classified as a lenticular galaxy. Both of these galaxies were digitised as stars in the GSC catalogue due to their bright cores.

  The group lies at a distance of perhaps 70 Mpc. The group is classified as a triple system in Alvin Huey’s guide to Galaxy Trios. Interestingly he does not include NGC 7782 as part of the triple but adds NGC 7781.

  Whilst NGC 7778 and NGC 7779 should be visible in relatively small instruments NGC 7781 will be far more of challenge with a listed blue magnitude of 15. It may be much brighter however in the visual, perhaps at 14th magnitude, nevertheless I would expect that from UK skies at least 40-cm will be needed to see it.

  The Night Sky Observer's Guide (NSOG) also includes a fifth galaxy, NGC 7780, in this group. Although probably not physically associated with the NGC 7782 group, NGC 7780 was discovered by Stephan in 1881 and independently by Swift in 1886. Both NGC 7780 and NCG 7781 are likely to be challenges for 45-cm telescopes according to the NSOG. NGC 7780 was host to sn 2001da. If these prove too easy then near NGC 7780 is MCG+1-60-44 for large telescopes.

  All five NGC galaxies should fit in the field of view of a medium power (240x) modern hyperwide (100 degree) eyepiece.

  If these galaxies are all too easy then try for RFGC 4209. I am not sure if RFGC 4209 will be visible in normal amateur class instruments however, perhaps some of the giant Dobsonians that seem to be around could give it a go. Here RFGC stands for the Revised Flat Galaxy Catalogue by Karachentsev et al. There are 4236 galaxies in this catalogue with axial ratios (a/b)B ≥ 7. Within this group RFGC 4209 would be classified as an Ultra thin. It is also known as LEDA 091829 but has no listed magnitude. It is not part of the group being much more distant. There is some interesting information and an image of this group at ManTrapSkies.

  Owen Brazell - Galaxy Section Director

• NGC 750 in Triangulum

  September 2019 - Galaxy of the Month

  The interacting galaxy pair NGC 750/751, also known as Arp 166, was first discovered by William Herschel in 1784, although he only saw one galaxy here. It took Bindon Stoney using Lord Rosse’s 72” at Birr to see the fainter companion galaxy NGC 751.

  The pair lie about 225 million light-years away in Triangulum and consists of a pair of elliptical galaxies. They may be only about 10kpc apart. The first interaction of this pair, which occurred about 100 million years ago, has drawn out a number of tidal tails. It is suggested that these two galaxies are still in the process of tidally interacting. Arp characterised them as galaxies with diffuse filaments.

  NGC 750 also appears to be part of a group of galaxies known as the LGG 42, although, with the exception of NGC 761, none of the other galaxies in the field appear to be part of this group. The field consists of a nice chain of galaxies including NGC 736, NGC 740 and NGC 761.

  There are a number of other NGC objects in this field but at least two of these, NGC 733 and NGC 760, along with NGC 737 are just stars. It is just possible that Stoney saw a faint galaxy near the star marked as NGC 733 so maybe it could be real but the historical evidence points to the star. Some software programs do however to assign the number NGC 733 to the galaxy rather than the star.

  The lower group of galaxies around NGC 736 including NGC 738 and NGC 740 were discovered by Stoney in 1850, again using the 72”, as part of their survey of objects discovered by William Herschel. Herschel discovered NGC 736 in 1784. Stoney also discovered the northernmost galaxy of the chain, NGC 761 in 1850. It took Ralph Copeland in 1874 to find the last NGC galaxy in the group, NGC 739, also using the 72”.

  Perhaps not surprisingly the NGC 750/751 pair also appears in the Vorontsov-Velyaminov (VV) catalogue of interacting galaxies as VV 189. What is interesting though is NGC 761 also appears in the VV catalogue as VV 425. NGC 761 is a nice spiral but there is also a fainter galaxy seen through the spiral arms. I suspect that this is a much more distant galaxy just seen in projection rather than an interacting system, however Vorontsov-Velyaminov added it as part of his M51 type systems. Interestingly NGC 736 also shows many shells which suggests signs of a recent interaction.

  Given that only two of the galaxies in this field were seen by William Herschel I suspect that the rest of the group maybe a bit of a challenge to see and will require medium to high powers and probably at least 40-50cm aperture. The whole group will fit in a medium power field, say 200x, using a modern hyperwide field eyepiece (Say an Ethos or equivalent 100 deg AFOV).

  The LGG 42 group appears to consist of 13 galaxies including NGC 750, NGC 751, NGC 761, NGC 777, NGC 783, NGC 785 and NGC 789 along with a few UGC galaxies. The group is also known as the NGC 777 group.

  Visually both Night Sky Observer's Guide (NSOG) and Luginbuhl and Skiff (L&S) suggest that the 750/751 pair can be split with apertures in the 30-35cm range but obviously larger apertures will make this easier. Interestingly NGC 750/751 and 761 also feature in the Webb Deep-Sky Society Observer's Handbook (WSDSOH) Volume 4 where the suggestion is to see much detail you would need 16” (40cm) aperture although the 750/751 pair can be glimpsed as a single spot with a 8¾“ (21cm) telescope.

  Owen Brazell - Galaxy Section Director

• NGC 7042 in Pegasus

  August 2019 - Galaxy of the Month

  August sees the return of astronomical dark to UK skies and also sees the 100th GOM. I can’t believe that so many of these have been written, almost 40000 words.

  For this occasion, I have chosen the galaxy pair NGC 7042/7043 in Pegasus. This may feel like an inauspicious choice for such a landmark column but it is getting progressively more difficult to find interesting objects that fit within reach of medium sized telescopes.

  NGC 7042 itself was discovered by William Herschel in 1784, but it took Albert Marth using William Lassell’s 48” speculum metal reflector to discover NGC 7043 in 1863.

  Both galaxies appear to be face on spirals and appear to be a physical pair. They both appear to be part of an 11 galaxy group designated as LGG 442. This group also contains the galaxies NGC 7015 and NGC 7025 as well as a number of UGC galaxies.

  NGC 7042/42 may be of the order of 210 million light years away, which would make NGC 7042 perhaps 110000 light years in diameter and NGC 7043 perhaps 70000 light years in diameter. Despite being physically associated NGC 7042 and NGC 7043 do not show any signs of tidal interactions.

  As both the discoverers described their respective objects as faint it is perhaps not surprising that they do not appear in any of the standard references such as the Night Sky Observer's Guide (NSOG) or Luginbuhl and Skiff (L&S). NGC 7042 does however make the H400 II observing program, which admittedly is mostly non-descript galaxies. NGC 7042 was also home to the Type Ia supernova SN 2013fw.

  Perhaps unsurprisingly given their nature there is not a lot of information in the research literature on either of these two galaxies as they would appear to be just run of the mill spirals.

  Visually NGC 7042 itself would appear to be visible in a 14” (32-cm) telescope but only as a faint glow. I am not sure what size telescope is needed to see NGC 7043, although I have seen an observation of it which suggests that with averted vision it may be visible in 30-cm, although I would think this observation may be questionable. NGC 7043 has a listed magnitude of 14.8B which suggest that it is probably around 14th magnitude in V. The tightness of the pair would suggest that high power can be used on them and keep both galaxies still in the field of view.

  Owen Brazell - Galaxy Section Director

• NGC 6500 in Hercules

  July 2019 - Galaxy of the Month

  Although the July skies are now starting to darken after the summer solstice at my latitude of 52N we don’t really get and truly dark skies until mid-August, as such and deep sky object chosen for observation this month must be by necessity rather bright.

  Accordingly I have chosen the galaxy pair NGC6500/6501 in Hercules as this month’s challenge. The pair were first discovered by William Herschel in 1799, although they were independently rediscovered by Stephan in 1880.

  The galaxies almost certainly form a physical pair. Both are spirals, although NGC 6501 maybe a lenticular, and NGC 6500 shows some distortion of its spiral arms that suggests a tidal interaction.

  NGC 6500 is classified as a LINER i.e. it shows emission lines in its spectrum. Sometimes these are from an AGN or some form of starburst. Observations seem to show that NGC 6500 seems to have a bipolar outflow coming out of it, although this is suggested to be more like to be a starburst wind, like that of M82, rather than a wind from a black hole. Observations in the UV suggest that they may be coming from an obscured population of WR stars which would back up the starburst theory.

  NGC 6500 along with NGC 6501 and NGC 6467 are included in LGG 414 along with 3 UGC galaxies making a small group of 6 galaxies. The group is probably at a distance of 140 million light-years which would make NGC 6500 about 90,000 light-years across and NGC 6501 about 85,000 light-years across, so very similar sizes and not far short of the size of the Milky Way. However there appear to be some disagreements as to its distance with some sources placing it around 200 million light-years away.

  There are numerous much fainter galaxies in the field, although interestingly one of the brighter ones does not seem to appear in the catalogues, probably because it is in the glare of STF 2245, although Howard Banich does draw it in his Object of the Week post at DeepSkyForum and suggests it is about 16th magnitude. He was using a 28” reflector though.

  The pair does not make it into either Luginbuhl and Skiff (L&S) or the Night Sky Observer's Guide (NSOG) which is perhaps rather surprising as there are reports of the pair being seen with a 22cm telescope from UK skies.

  Nearby in the same medium power field are two much fainter elliptical galaxies NGC 6490 and 6495, both discovered by Marth in 1864 with Lassell’s 48” reflector in Malta. These are much further away and not associated with the NGC 6500 grouping. These will be challenges for telescopes in the 45-50cm telescope class I would think.

  Also in the field is the coloured double star STF 2245 for those amongst our members who enjoy all forms of deep sky objects.

  As an aside I must apologise for the quality of the Megastar chart. Unfortunately, Megastar has stopped being able to download DSS images due to changes in the URL and it is unclear if this will be fixed so I may have to move to another charting program going forward.

  Owen Brazell - Galaxy Section Director

• NGC 5954 in Serpens Caput

  June 2019 - Galaxy of the Month

  The summer months in the UK are not really dark enough for any kind of astronomical observing, let alone galaxy observing. As such I have chosen a relatively bright pair of galaxies in NGC 5953 and NGC 5954, collectively known as Arp 91 for this month’s column.

  This pair of galaxies in Serpens Caput was first discovered by William Herschel in 1784. William Herschel was able to split the pair and recorded it as a double nebula.

  Both NGC 5953 and NGC 5954 are individually classified as active galaxies with NGC 5953 being classified as a Seyfert type 2 with a circumnuclear ring and NGC 5954 being classified as a LINER.

  The interaction between the pair has caused areas of star formation in the nuclear regions and as such it is unclear that the nuclei are truly active or we are just seeing the emission from massive star burst regions in the centre. Its interacting nature also meant it was included in the earlier catalogue of interacting galaxies by Vorontsov-Velyaminov as VV 244.

  It is believed that the pair lies at about 96 million light-years from us. Both of the galaxies in the pair appear to have the same mass but NGC 5953 is the more disrupted of the pair with tidal tails and plumes surrounding it.

  Arp 91 is included in the galaxy group LGG 400 which also includes NGC 5951 and NGC 5962 as well as UGC 9902. This classification may be based on spatial coincidence rather than redshift data.

  Visually because of the closeness of the pair this is going to require high power to split. Night Sky Observer's Guide (NSOG) thinks the group is a target for 16/18” telescopes but it should be visible as a nebulous patch in much smaller telescopes, after all William Herschel’s 18.7” speculum metal telescope was probably equivalent to a modern 11-12”, although I am sure that some would claim they can see all the H2500 with much smaller instruments. However observations with a 14” from UK skies suggest that both NGC 5954 and 5953 are both small and faint.

  About 16’ away from the Arp 91 pair is the edge on spiral NGC 5951 and all three galaxies will fit in a medium power field. NGC 5951, as it is an edge on galaxy, may also require a telescope in the 40-cm class to see.

  The galaxies did make it as an Object of the Week (OOTW) at the DeepSkyForum. Alvin Huey suggests in his Arp Observing Guide that with his 22” and a magnification of around 500x he scan see the extension between NGC 5953 and NGC 5954.

  Interestingly in ST4I the group is listed as the NGC 5953, 5954, 5951 Trio. I have no idea where this naming came from, although it does appear in Alvin Huey’s listing of Galaxy Trio’s, it is not as far as I can see in Miles Paul’s listing of triples.

  Owen Brazell - Galaxy Section Director

• Hickson 62 in Virgo

  May 2019 - Galaxy of the Month

  With the skies nominally no longer dark from May onwards at my latitude to see any galaxies at all means I need to choose brighter targets. This month it is the bright galaxy group Hickson 62.

  The main pair here are NGC 4776 and NGC 4778. Both of these galaxies were discovered by John Herschel in May 1836. The third NGC galaxy in the group, NGC 4761, was discovered by Tempel in 1882 along with the fourth galaxy NGC 4764.

  By today’s standards Tempel was using a relatively small telescope in an 11” refractor but he was an exceptional observer and he described them as eF, so they are going to be a challenge to find.

  As seems often in the NGC there is some confusion here about the designations and it appears that William Herschel did see the brighter galaxy pair but could not resolve them into two so he described it as a double nebula and it was entered into the NGC as NGC 4759. Continuing confusion comes with some of the professional databases like SIMBAD where NGC 4778 is equated with NGC 4761, which is the small galaxy NE of the double pair. Even the identity of NGC 4764 is uncertain because Tempel did not give Dreyer co-ordinates and they made up a position for it.

  As such there is a wide variation in sky charting programs as to what galaxy is which. Skytools for instance appears to have a confused set of designations in both SkyTools 3 and 4. SkySafari 6 appears to fit the corrected NGC view of the group.

  Views of the group are going to be complicated by the 8th magnitude star situated in the middle of the group of galaxies. The compact nature of the group also suggests that you are going to need to use high power on it to separate the a/b pair and probably to bring out the others.

  Hickson 62 is interesting because it is one of the closest compact groups and by studying it in X-Rays with Chandra we can see a very hot (several million degree) intra cluster medium. This intra cluster medium is not smooth and appears to have several cavities in it which may be what is stopping a classical cooling flow happening. These cavities could be the remnants of radio lobes from the past when NGC 4778’s central engine was more active.

  Currently NGC 4778 is classified as a low luminosity AGN. Observations of NGC 4778 also suggest that it may have had a recent merger with a much smaller galaxy. NGC 4778 is classified as an S0, a lenticular, as indeed is NGC 4776. The other two galaxies in the group are also either elliptical or lenticulars. The group appears to be at a distance of about 60Mpc.

  Observationally NGC 4778 appears in Luginbuhl and Skiff (L&S) under the NGC 4759 moniker where they suggest that it may be visible as a faint patch with a 15-cm. I would think that from UK skies at least 20-cm would be needed to repeat that observation. Interestingly the pair do not appear in the Night Sky Observer's Guide (NSOG) under any designation. The group is part of the Astronomical League Galaxy Groups and Clusters list.

  Owen Brazell - Galaxy Section Director

• NGC 6109 in Corona Borealis

  April 2019 - Galaxy of the Month

  The small group of galaxies around NGC 6109 were discovered by Edouard Stephan over several nights in July 1880 using the Foucault designed 31” silver on glass reflector at Marseille, they must have dark nights in the summer there and good weather as the telescope seems to have sat outside rather than in any kind of enclosure.

  The group of galaxies including NGC 6109 is also included in the WBL catalogue as number 612. It lists 10 galaxies including NGC 6105, NGC 6107, NGC 6108, NGC 6109, NGC 6110, NGC 6112, NGC 6114 and NGC 6116 as being part of the group. The group appears to be known after its brightest galaxy, NGC 6107. It is considered to be a dynamically young poor cluster.

  Zwicky also noted this group as a cluster with the designation Zwicky 1615.8+3505. The Zwicky cluster listing also included NGC 6104 as part of the group but it is quite a long way out from the main group and the WBL listing does not include it as part of the group. It is also odd in that only NGC 6104 shows any signs of star formation.

  The group forms a nice line of galaxies but as Stephan found them faint these may turn out to be a bit of a challenge.

  NGC 6109 is both a radio source and a point X-Ray source and is currently classified as a LINER type AGN with an unusual doughnut shaped jet. Oddly for a galaxy of this type it is suspected to be an S0, lenticular. It also shows a typical head-tail radio structure, which is unusual as these galaxies are normally only found in rich clusters of galaxies, although this interpretation has been challenged and various models have been put forward to explain this feature, including a deflected jet. NGC 6109 was also home to supernova 2010an.

  With the exception of NGC 6107, which is classified as an elliptical (E3?), most of the galaxies in the group are suspected to be spirals. NGC 6107 is also a radio and X-Ray source. The group is suspected to be about 400 million light years away.

  There are also a large number of much fainter galaxies in the field which may be visible in very large amateur telescopes. Steve Gottlieb in his NGC notes describes all of the galaxies in the group as faint with an 18” from good skies so they are likely to challenge 20” and above from typical UK skies. Both NGC 6107 and NGC 6109 are included in the Night Sky Observer's Guide (NSOG) Volume 2 as targets for 16-18 inch telescopes.

  Owen Brazell - Galaxy Section Director

• IC 2184 in Camelopardalis

  March 2019 - Galaxy of the Month

  This peculiar V shaped galaxy pair in Camelopardalis was first discovered in 1900 by Bigourdan using the 12.4” refractor in Paris.

  Originally thought to be a single galaxy it was added into Vorontsov-Velyaminov’s catalogue of interacting galaxies as VV 644. Due to its bright emission in the UV/Blue bands it was also classified as Markarian 8.

  There seemed to be a lot of confusion as to the nature of this object with some observers claiming there were four galaxies present. This mystery was cleared up when Hubble imaged the pair. The Hubble image shows distinct tidal tails as well as the massive star forming regions formed when the gas from the galaxies crashed into one another.

  The presence of these star forming regions and the existence of many Wolf-Rayet stars has also led to IC 2184 being classified as a Wolf-Rayet galaxy. Wolf-Rayet (WR) galaxies are a subset of emission-line and HII galaxies, whose integrated spectra show broad emission features attributed to the presence of WR stars.

  Images taken in H-Alpha show the existence of a number of bright knots, which are the starburst sites. These knots would appear to be immersed in a diffuse envelope. The rapid rate of star formation is indicated by the fact that one of the knots may have up to 850 WR stars in it. Given this the knots cannot be that old and their age has been estimated of to be of the order of 4-6 million years. The existence of these knots may be the reason that earlier observers thought there were more than two galaxies here.

  From the Hubble image it would appear that we are pretty much seeing the galaxies edge on. The galaxies are perhaps 165 million light-years away and at this distance would be perhaps 45 and 40 thousand light-years across. The whole system is perhaps 65 thousand light-years across, so quite small galaxies. The pair will merge into a single galaxy and given their distance will have probably done so by now.

  Visually this galaxy pair will be a challenge, not so much for their faintness as they are around 13th magnitude, but because of their size. They are quite small so you are going to need high power to separate the pair.

  Perhaps not surprisingly IC 2184 does not make the standard references. Steve Gottlieb has quite an old observation in his IC notes which suggests that it was fairly faint with a 24” reflector and even at 375x he could not split the pair. I guess it has not made it onto the list for Jimi Lowery’s 48”. Uwe Glahn does have a nice drawing of the pair however with his 27” in the Interstellarum Field Guide.

  Owen Brazell - Galaxy Section Director

• NGC 2585 in Hydra

  February 2019 - Galaxy of the Month

  In 1886, whilst observing with the 26.3” refractor at the University of Virginia’s Leander McCormick Observatory, Frank Muller came across a group of what he believed were four new nebulae.

  Unfortunately the observers at the Leander McCormick observatory were notorious for their poor reported positions for newly discovered nebulae and in this case the positions that he gave Dreyer were at least an arc-minute out.

  Based on the descriptions Muller gave however, Dreyer was able to associate three of the nebulae with a small group of galaxies which later became catalogued as NGC 2583, NGC 2584 and NGC 2585. The fourth object that Muller discovered was later determined to be a triple star, although the number NGC 2586 has sometimes been erroneously assigned to another nearby galaxy MCG -1-22-12.

  Two of the galaxies, NGC 2584 and NGC 2585 appear to form a physical pair and show signs of tidal interactions. They were given the number 1225 in the extended VV (Vorontsov-Velyaminov) catalogue of interacting galaxies. As the extended catalogue was never published in a journal (only online) the VV numbers beyond 835 are not included in the main extragalactic databases such as NED.

  There is conflicting information about whether NGC 2583 forms part of the group but its distance and redshift suggest it probably doesn’t.

  The two NGC galaxies are going to be challenging to see visually as they are at around 13-14th magnitude. If they are not challenging enough then there are two other galaxies that appear in the same field as NGC 2584/5 that have catalogue numbers from the MCG (Morphological Catalogue of Galaxies) catalogue at around 15th magnitude as MCG -1-22-6 and MCG -1-22-7.

  There are suggestions that they may also form part of a physical group with NGC 2584/5. Their redshifts are quite similar to the main pair, although the redshift of MCG-1-22-6 is perhaps a little further from that of NGC 2583. The redshift of NGC 2585 is around 6868 km/s whilst that of MCG-1-22-6 is 6590. Similar to the issues with NGC 2583 however, if the distances/redshifts associated with them are correct then it is perhaps unlikely unless the group is very widely spread in space. At a stretch MCG-1-22-12 (the galaxy erroneously assigned NGC 2586) could also be part of the group as its redshift is similar to that of NGC 2585. The group is not assigned any number in either the WBL or LGG catalogues which suggests that they at least did not see it as a physical cluster.

  The group is very small and will be challenging to find as, despite the fact it lies in the northern part of Hydra as it does not rise much above the 30 degree (one airmass) altitude line as seen from the southern UK.

  It is tight enough that all the galaxies in the main group should appear in the field of a medium power (say 250x) eyepiece. MCG-1-22-12 is slightly further away but even then it should fit in the same field as the others with a modern hyperwide eyepiece at say 200x. It may be worth using this kind of power to help darken the sky background and try and bring the galaxies out.

  NGC 2585 is a barred spiral galaxy and NGC 2584 is an Sc spiral with lots of ongoing star formation and as they both appear to be face-on spirals probably only the core will show. NGC 2583 is an elliptical galaxy. As always when observing galaxies try and find a dark site with little light pollution.

  Owen Brazell - Galaxy Section Director

• NGC 1622 in Eridanus

  January 2019 - Galaxy of the Month

  NGC 1622, along with NGC 1618 and NGC 1625 form a nice triplet just north of the bright star Nu Eri.

  The discovery history of the group is quite interesting as they are all relatively bright galaxies. NGC 1618 was found by William Herschel in 1786, NGC 1625 by John Herschel in 1827 whilst reobserving his fathers’ discoveries and NGC 1622 by George Stoney whilst using Lord Rosse’s 72” at Birr in 1850.

  NGC 1622 was also independently discovered by d’Arrest on the 1st Jan 1862 using the 11” Refractor at Copenhagen, no New Year’s Eve’s parties for him! You would have thought that William could have picked up NGC 1625 as well, although NGC 1622 may have been to faint for him. Perhaps scattered light from Nu Eri impacted his observations.

  John Herschel originally thought that the discoveries by Stoney and d’Arrest were two separate objects and added them into the GC as such (numbers 881 and 878). Dreyer spotted the error and merged both into NGC 1622.

  The galaxies may form a physical system as they all have similar redshifts. All three are spiral galaxies with an inclination close to edge on, with the exception of NGC 1618 which is rather wider open.

  None of the galaxies show any obvious signs of interactions, although the outer disk of NGC 1622 does appear to show quite a strong warp. NGC 1625 also seems to show a slight warp in its disk and also appears to have a galaxy superimposed on its disk. Given the radial velocity of the object it may well be a dwarf galaxy associated with NGC 1625. The group would appear to be about 220 million light years away.

  All the galaxies in the group appear to be barred spirals which is relatively unusual. Of the three it would appear that NGC 1618 is the one most actively forming stars at this time.

  The group is tight enough that it will fit in the field of a modern hyperwide eyepiece at medium power. The Night Sky Observer's Guide (NSOG) suggests that it is a tough target for 8-10” telescopes but should be easy in 14-18” ones.

  I suspect the main challenge seeing the galaxies here is going to be keeping the 4th magnitude star Nu Eri out of the field whilst looking for the galaxies, a similar challenge to that with NGC 404 and Mirach in And. The galaxies are quite faint and may well require a telescope in the 40-cm plus category to show well, especially from UK skies.

  If these are not enough of a challenge then the compact group Hickson 30 lies only 20’ north of NGC 1622. Hickson 30 contains no NGC galaxies, although the brightest galaxies are around 14th magnitude so it should be visible in larger scopes.

  Owen Brazell - Galaxy Section Director