Galaxy of the Month in Cetus

• NGC 533 in Cetus

  December 2022 - Galaxy of the Month

  This month’s challenge is the galaxy pair in Cetus including NGC 533 and NGC 521. There is also a third galaxy in the field in IC 1694. NGC 521 and NGC 533 were discovered by William Herschel in 1785. IC 1694 was discovered in 1891 by Bigourdan using a 12.4” refractor. The group will best be seen in the early evening this month.

  The RC 1 suggested that NGC 521 and NGC 533 form a physical pair, however they do not appear to be interacting and their distances do appear to be somewhat different. NGC 533 is described as an elliptical galaxy with a classification of E3. It is also classified as a cD galaxy, which would be the brightest and largest galaxy in a cluster. NGC 521 is a face on low surface brightness spiral, classified as SB(r)bc. The GALEX images in the UV indicate the NGC 521 is undergoing a lot of star formation in its spiral arms.

  Interestingly NGC 533 is suggested to be part of the galaxy cluster Abell 189 although NGC 521 which is in a pair with it is not, although they are very much brighter than the other galaxies in the cluster and somewhat offset from it. The distances for NGC 521 and 533 are also very different so it may be that they are just an optical pair. NGC 533 Is also surrounded by many faint galaxies. The cluster ACO 189 is also much further away than either of the NGC galaxies. NGC 521 lies at a distance of perhaps 34 Mpc whilst NGC 533 would appear to be almost twice as far away at perhaps 70Mpc.

  NGC 521 has produced 3 supernovae since 1966.

  IC 1684 is also suggested to be part of Abell 189 and thus associated with the NGC 533/521 pair, however although it is not well studied its distance lies at around 50 Mpc so in these terms at least it would not be associated with either ACO 189 or the other two galaxies. All in all this is quite a confused field and it may be that none of the galaxies are associated.

  Perhaps surprisingly Night Sky Observer's Guide (NSOG) Vol.1 suggests that much can be seen of this pair with telescopes in the 20-25cm aperture. However, to see IC 1694 will require telescopes in the 45-50cm range. I suspect that many of the observations used in the NSOG may have been from high altitude, and from the poorer skies of the UK 30cm may be required to see much. All three galaxies are close enough together that they will fit in the field of view of a medium power hyperwide eyepiece. To find IC 1694 however is likely to require a high power. The much fainter galaxies around NGC 533 are probably out of visual range but should be picked up by EAA systems.

  Owen Brazell - Galaxy Section Director

• NGC 833 in Cetus

  November 2020 - Galaxy of the Month

  NGC 833 is part of a quartet of galaxies including NGC 833, 835, 838 and 839 that together make up the galaxy group Hickson 16.

  All four were discovered by William Herschel on the same night in November 1785. NGC 833 is also included in the Vorontsov-Velyaminov extended catalogue of interacting galaxies as VV 1007. The original VV catalogue had only 852 members but was extended by his students by adding an extra 1162 systems. The group is also known as Arp 318 and that may consist of the 4 galaxies in the Hickson 16 group as well as NGC 848, which appears to be at the same distance as the others.

  NGC 848 is somewhat fainter than the others and was discovered by Ormond Stone in 1885 and then independently by Swift in 1886. NGC 848 appears to have undergone strong gravitational interactions as well. Arp described it as a part of his group of galaxies with faint, diffuse streamers, peculiar galaxies.

  The group is at a distance of about 160 million light-years. All of the galaxies in the group show signs of interactions and most of the galaxies in the group are mild AGN’s either LINER’s or Seyfert 2 types. There are suggestions that a number of galaxies in the group may have undergone major merger events in the relatively recent past.

  The group is also part of a larger conglomeration of seven galaxies catalogued as LGG 49 which also includes NGC 873 as well, which I am slightly surprised about as it is at least 2 degrees away from the others on the sky.

  NGC 838 and 839 are probably star burst dominated galaxies as they show no signs of the expected continuum of an AGN in X-Ray observations. Observations with the XMM—Newton satellite however suggested that NGC 839 is probably an obscured AGN. Hickson 16 is thought to have one of the highest concentrations of starburst/AGN activity in the local universe. Interestingly all the galaxies in the group appear to be spirals.

  As one of the brighter Hickson groups the core group of HCG 16 should be visible with difficulty in 20-cm but relatively easily in say 37-cm. The galaxy group, including NGC 848, is pretty tight so should be visible in a medium power hyperwide eyepiece, say 250x. The Night Sky Observer's Guide (NSOG) suggests that perhaps 30-cm is required to see them well, although there is no mention of NGC 848 so this may be more difficult to find, perhaps not a surprise as it was missed by Herschel. NGC 835 is the brightest member of the group.

  For observers from the southern UK the group only just makes the 30 degree line so it is best to catch when within two hours of the meridian.

  The group (as Hickson 16) made the Deep Sky Forum (DSF) forum object of the week in 2014. There are also observations of the group at Adventures in Deep Space. For owners of large telescopes there are a number of other faint and probably unrelated galaxies in the field.

  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

• ACO 194 Group of Galaxies in Cetus

  November 2017 - Galaxy of the Month

  Our object this month is the galaxy cluster in Cetus ACO 194.

  The cluster has not been well covered in amateur observing guides despite it having a number of pages dedicated to it in the venerable Webb Deep-Sky Society Observer's Handbook (WDSSOH) Vol. 5. It does not appear in Night Sky Observers Guide (NSOG) or in Luginbuhl and Skiff (L&S) much to my surprise. There is a small piece on it in the book Galaxies and How to Observe them.

  This may be due to it low altitude it culminates at as seen from northern latitudes. The galaxies themselves are not so bright and although there are 14 galaxies in the NGC listed in the group most are quite faint.

  The main galaxies in the group NGC 545 and NGC 547, also known as Arp 308, were discovered by William Herschel in 1785, whilst it took d’Arrest to find the next brightest, NGC 541, almost 100 years later in 1864. Most of the other NGC galaxies in the group were found by Swift and d’Arrest.

  The cluster is classed 0 based on its Abell richness class and structurally it is classed as L on the Rood-Sastry class.

  The SAO/NASA ADS Astronomy Abstract Service provides a link to the PDF of the paper "Tuning Fork" Classification of Rich Clusters of Galaxies describing the cluster classification schemes.

  Basically the classification suggests that it is a linear string of galaxies. Of course this can only ever be a 2D representation of the cluster as we have no idea of their motions in the plane of the sky. Richness class 0 objects are the least impressive of all the Abell clusters as they contain the least number of bright galaxies but ACO 194 is close enough (in Abell cluster terms) to show a number of galaxies.

  The group is also interesting because it contains a strange galaxy known as Minkowski’s object. Originally thought to be a dwarf galaxy it is now thought to be a cloud of gas in the inter galactic medium that has been compressed by the radio jet from NGC 541 to form a bunch of stars.

  There is an interesting discussion about it to be found in the GalaxyZoo Forum and it was also the Deep-Sky Forum (DSF) object of the week in November 2014.

  

  Minkowski’s object is the bluish object to the left of NGC 541 in the SDSS image and you can see a more detailed view in the Hubble legacy image. Not unsurprisingly given its colour it is very bright in the UV images from GALEX.

  

  There is some discussion over whether this object can be seen with amateur scopes but it will certainly require a large aperture at high power I think to find.

  Interestingly it would seem that NGC 541 along with NGC 545 and NGC 547 have interacted in the past as there is some evidence of a star stream between them. The centre of the cluster is probably around NGC 541 itself. Both NGC 541 and 545 show large radio jets and lobes.

  Visually I guess that the brighter galaxies in the group could be seen with 35-cm telescopes but to get all the main NGC galaxies from UK latitudes will probably require 50cm.

  Andrew Robertson and I observing with 55 and 60-cm telescopes at the recent Kelling Heath star party counted at least 14 galaxies in the group, perhaps 16 although we may have double counted. It is not always so easy when going along a linear group to make sure that some galaxies have not already been seen. We did not stray much off the main band and therefore would not have picked up the outlying NGC objects, something to go back for.

  I would suggest that to pick up the fainter galaxies will require a high power and possibly a driven telescope. A chart may have also have helped to track them down.

  Coincidentally the November 2017 edition of Sky and telescope also carries an article on ACO 194. There is also an interesting article on observing ACO 194.

  Owen Brazell - Galaxy Section Director

• November 2013 - Galaxy of the Month

  NGC 1055 in Cetus

  

  Image Courtesy of Ken Crawford, California. For more images from Ken Crawford please visit the Rancho Del Sol Observatory website. You can click on image for a high resolution version, or download a copy of our Megastar© Finder Chart of the NGC 1055 and M77 region.

  NGC 1055 was first discovered by William Herschel in 1783 from Slough. It is an edge on spiral galaxy not dissimilar to M104 (the Sombrero) in Virgo. The dark dust lane and bright star forming regions are believed come from its interaction with the nearby spiral galaxy M77. Indeed a low power eyepiece view will show both galaxies in the same field as they are only separated by about half a degree (a full moons width).

  There is a nice image showing galaxies at NASA's APOD. The interaction with M77 also means that NGC 1055 is a bright infra-red and radio source. Images in the ultraviolet by the GALEX satellite show the blue star forming regions very clearly even though they may be overshadowed by the dust lanes. The disk as indicated by the dust lanes appears warped which is also probably a result of the interaction. NGC 1055’s nuclear region also shows some of the properties expected form a LINER galaxy although it is not clear if it is one. It does appear quite boxy and large.

  Current distance measurements place NGC 1055 at 45—60 million light years and if this is so then the spatial distance between M77 and NGC 1055 is probably only about 500,000 light years, less than a quarter of the distance between ourselves and M31. This distance would also give NGC 1055 a diameter of about 100,000 light years, comparable in size to our own Milky Way.

  Detailed images of NGC 1055 show structures in its halo that may well be star streams from disrupted companion galaxies.

  NGC 1055 is one of the dominant members along with M77 of a small group of galaxies known as the M77 group which also includes the galaxies NGCs 1055 (type Sb) and 1073 (type SABc), as well as UGCs 2161 (DDO 27, type Im), 2275 (DDO 28, type Sm - designating a morphological type between spirals and irregulars) and 2302 (DDO 29, type Sm), and the irregular galaxy UGCA 44 and the SBc barred spiral Markarian 600.

  NGCs 1087 (Sc), 1090 (S-), and 1094 (SABb-) although nearby on the sky are actually background galaxies, as their much higher redshift indicates.

  The M77 group is about the same distance from us as the Virgo cluster but in a different direction. Visually NGC 1055 maybe more challenging to get details out of than images may suggest and although it may be seen in relatively small telescopes to see any detail is likely to require a telescope of 30cm or above aperture in typical UK skies.

  Owen Brazell - Galaxy Section Director

• October 2011 - Galaxy of the Month

  Wolf-Lundmark-Melotte

  

  Image Courtesy of Philip Massey & Survey Team Lowell Observatory. Click on image for a larger version. For the original image click here - Warning this is a 14MB file!

  With the coming of Autumn the Milky Way and its attendant nebulae and star clusters start to depart from our skies and we start seeing back into deep space and the realm of the galaxies and is the best time to try for some of the more southerly objects.

  This month’s challenge, Wolf-Lundmark-Melotte (WLM) is a lot more difficult to see than some of the previous galaxy of the month objects and will need dark transparent southern skies to find. It has been seen with telescopes as small as 33cm but I suspect will need a larger one from your average UK skies.

  WLM is an irregular galaxy, although it has also been classified as a dwarf E5 elliptical, which is on the fringes of the local group. First discovered by Max Wolf in 1909 photographically and it was discovered to be a galaxy by Lundmark and Melotte in 1926.

  The distance to WLM has been controversial but the latest results place it at about 2.9 million light years. WLM is one of the most isolated members of the local group, its nearest neighbour is IC1613 which is almost 1 million light years away.

  WLM has a halo of very old stars that date back to the earliest formation of our local group and these stars are substantially older than the stars in the core of the galaxy. The fact that the galaxy is so isolated and so small (it has a major axis of around 8000 light years but it is very elongated) suggests that the halo probably has not come from cannibalization of another small galaxy but formed with it and has remained undisturbed since that time.

  As WLM is located in the southern reaches of the constellation of Cetus along with its large size (11.5 x 4.2 arc minutes) it is going to be a challenge to find from northern latitudes. The other challenge is finding it with popular star charting software as it has the designation UGCA 444 (after an extension to the UGC catalogue) but perhaps will be easiest find by either its MCG designation -03-01-015 or its PGC designation 143. It does also carry the designation DDO 221 from the David Dunlap Observatory catalogue of dwarf galaxies.

  It appears that WLM has only one known globular star cluster which is slightly unusual even for galaxies this small.

  My only observations of this galaxy are with a 24" from Tenerife and even then it was quite faint.

  UGCA 444 RA: 00h 01.948m Dec: -15° 27.02' Mag: 11.0 (B) Size: 11.6'x4.0'

  Owen Brazell - Galaxy Section Director