Galaxy of the Month in Cancer

• NGC 2563 in Cancer

  January 2020 - Galaxy of the Month

  The small group of galaxies around NGC 2563 was once through to be part of a larger group known as the Cancer I cluster however this has been shown just to be a collection of disparate groups of galaxies and is not a true cluster. The cluster is now better known as the NGC 2563 group.

  The brightest galaxies in the group, NGC 2562 and NGC 2563, were discovered by William Herschel in 1787. NGC 2560 and 2569 were discovered by d’Arrest in 1862 using the 11” refractor at Copenhagen and NGC 2570 by Copeland in 1873 using Lord Rosse’s 72” at Birr.

  The group is also catalogued as WBL 178, a group of 11 galaxies which also includes the galaxies NGC 2556 but not NGC 2569 and NGC 2570. The group is also included in the LGG catalogue as LGG 158, a group of 14 galaxies which includes the NGC galaxies 2558, 2562, 2557, 2563, 2556, 2560 and 2569, showing how different selection criteria can include different objects.

  A much deeper study has suggested that there may be as many as 64 members of this group, although many are small and faint. NGC 2563 is definitely the brightest cluster galaxy (BCG) for this group and most, if not all, of the galaxies in the core of the group are lenticulars which suggests this is quite an old group. It appears that galaxies on the outside edge may well be still joining the group as they are still gas rich spirals.

  The group is also bright in X-Rays and observations suggest that most of the gas has been stripped from the galaxies by RAM pressure stripping and there are signs of interactions within the group, although mostly from observations in the radio region in the 21cm band. The X-Ray emission is probably coming from the hot gas between the galaxies. The group appears to be about 228 million light-years from us.

  Observationally the core of the group is quite compact and will fit in the field of view of a medium power eyepiece. If we assume that all the galaxies in the LGG list are actually part of the group then the whole group spans about 45’ on the sky.

  There are observations of this group in the book 'Galaxies and How to Observe Them' by Steinicke and Jakiel and also in Night Sky Observer's Guide (NSOG) Volume 1 where they suggest the two brighter galaxies are targets for 12-14” telescopes. There is no individual coverage of the other galaxies in the group there although there is a sketch showing NGC 2560, NGC 2562 and NGC 2563. Luginbuhl and Skiff (L&S) suggest that a 25cm telescope maybe needed to show NGC 2562 and NGC 2563. There are many other fainter galaxies in the core of the group that large telescopes and EAA systems may pick up.

  Of particular interest is the galaxy UGC 4332, which appears to be undergoing some form of merger from the distortions visible in it. Observations of the fainter members of the group maybe hampered by the 6th magnitude star just south of it so the use of high power is recommended to keep it out of the field of view.

  Owen Brazell - Galaxy Section Director

• January 2016 - Galaxy of the Month

  NGC 2513 Group in Cancer and Canis Minor

  This interactive image of the NGC 2513 group was provided by the Sloan Digital Sky Survey using Aladin Sky Atlas. We also have a finder chart should help you locate these galaxies.

  NGC 2513 on the Cancer/Canis Minor border is the brightest galaxy in a small group. First discovered by William Herschel in 1786 NGC 2513 shines at about 12th magnitude. To its west are two much fainter NGC galaxies first found by Bindon Stoney in 1851 using Lord Rosse’s 72” telescope and catalogued as NGC 2510 and 2511.

  These are all part of a poor galaxy group catalogued as WBL 169. The only other galaxy in the group with a common number is the nearby edge on spiral UGC 04171. The WBL catalogue however lists 9 galaxies in this group but most of the others are not assigned names. They are probably the CGCG galaxies mentioned below. Steve Gottlieb with his 17.5” saw 5 galaxies in the area surrounding NGC 2513.

  The three NGC galaxies appear to be either elliptical galaxies or lenticulars, although NGC 2511 may be a spiral. Two of the others in the group which have assigned types appear to be spirals. The core trio of 2510, 2511 and 2513 was included in Miles Paul’s atlas of galaxy trios (available from the Webb Society) and has in fact featured in DSO 134 in an article on galaxy trios by Al Lamperti.

  

  Detailed kinematic studies of NGC 2513 suggest it may be a triaxial spheroid from the motions of its stars. The group is thought to lie at a distance of about 200 million light years from us. The other galaxies in the group are probably CGCG 59-19, CGCG 59-21 CGCG 59-26, CGCG 59-27 along with UGC 04171.

  As UGC 04171 is an edge on spiral this is likely to be quite difficult to observe so the best candidates outside the NGC galaxies are probably going to be 59-19 and 59-27. Neither of these will be easy and will probably need a large telescope from a very dark site to find.

  The whole group should fit in medium power eyepiece field but the presence of an 8th magnitude star in the same field may make them a little harder to find. I was surprised to find that the group has not made any of the standard references such as the Night Sky Observer's Guide (NSOG). It is likely that an aperture of 40cm or greater will be required to see the main trio and perhaps 50cm+ to see the others, certainly if you are not working from high altitude skies.

  The group is also part of the Astronomical League’s galaxy cluster list so should perhaps be better known than it appears to be.

  Owen Brazell - Galaxy Section Director

• January 2015 - Galaxy of the Month

  NGC 2749 in Cancer

  

  This image was provided by the Sloan Sky Survey, and this finder chart should help you locate these galaxies.

  The constellation of Cancer is often overlooked except as a stepping stone between the two richer constellations, in terms of deep sky objects, of Gemini and Leo and if it is considered at all it is for the two open clusters M44 and M67.

  The constellation does however have its fair smattering of faint galaxies. Indeed there are over 100 galaxies catalogued in the NGC alone and whilst those hidden amongst the stars of M44 have often been mentioned there is a nice group around NGC 2749.

  NGC 2749 itself is a 12th magnitude elliptical galaxy (E2) discovered by d’Arrest in 1862 and is perhaps the brightest of the group. NGC 2745 and 2747 were discovered by Marth along with NGC 2751 and 2752. Remember though that Marth was using Lassell’s 40” speculum metal reflector from Malta so these galaxies are going to be a challenge. Oddly the other galaxy in the field NGC 2744 was discovered by William Herschel so how he missed 2749 must be a mystery as it is a brighter galaxy.

  The group is listed as number 202 in the WBL catalogue of poor galaxy clusters with a total of 5 galaxies counted as part of the cluster. These are NGC 2745, 2749, 2747, 2751 and 2752. The group would appear to be at about 192 million light years from us. Interestingly 2744 was not counted by WBL to be part of the group despite showing obvious signs of interaction. With the exception of NGC 2749 all the other galaxies in the group appear to be either spirals or lenticular (2745).

  Although the WBL catalogue does not include NGC 2744 within the group more recent papers suggest that in fact NGC 2749 and NGC 2744 are an interacting pair. Here NGC 2749 is classified as a low luminosity AGN (LLAGN). Fundamentally this is not that dissimilar to the activity (or lack of it) we see from the centre of our own galaxy.

  The faintness of these galaxies suggests that probably a 30cm telescope will be needed to see NGC 2749 and probably 40cm to find the others, although they will require a dark sky. There seem to be few images of this group so they may also make an interesting target for imagers. The classic references such as NSOG and L&S do not make much mention of the galaxies in this area apart from NGC 2479.

  Owen Brazell - Galaxy Section Director

• February 2013 - Galaxy of the Month

  Compact Galaxy Group Hickson 37

  

  Image Courtesy of the Sloan Digital Sky Survey (SDSS). You can click on image for a high resolution version.

  The constellation of Cancer is often thought to be a dead area apart from the open clusters M44 and M67. Although there are a large number of faint galaxies in Cancer most of the recent attention on these has focused on the galaxies within M44 itself. One of the overlooked groupings is the compact galaxy group Hickson 37. The group itself consists of five galaxies, the brightest of which is NGC 2783.

  NGC 2783 itself was first discovered by William Herschel in 1785 but the rest of the galaxies were far too faint for him to see. It is sometimes classed as an elliptical galaxy (E7) but also as a lenticular (S0).

  The second galaxy in the group IC 2449 (UGC 4856) was discovered by Javelle in 1903 using a 30" refractor. There is some confusion with the naming here as this galaxy is sometimes referred to as NGC 2783B. This error appears to come from the fact that Javelle used the wrong right ascension (RA) offset when he calculated its position and the RNGC added the B suffix. Very few modern atlases give the right name for this object. NED suggests that this galaxy is a LINER, a mild form of active galactic nucleus (AGN).

  The remaining members of the group are much fainter, being around 16th magnitude. Realistically to see any of the galaxies in Hickson 37 visually is going to be a target for 18 inch and above telescopes and even telescopes with an aperture of 22" may only pickup 3 of the galaxies in the group, usually a, b and occasionally c.

  It would however be an interesting target for imagers and there are very few amateur images of the group. One image taken with the Faulkes North telescope can be found on the Planet SI blog.

  Most of the Hickson groups are thought to be in the process of merging into elliptical galaxies. It has however been suggested that many, if not all, Hickson groups are the cores of generally elongated loose groups of galaxies and as such may be dynamically stable over longer time spans that perhaps thought.

  Owen Brazell - Galaxy Section Director

• January 2012 - Galaxy of the Month

  NGC 2775 in Cancer

  

  Image Credit/Copyright - Adam Block of Mount Lemmon SkyCenter / University of Arizona. Click on the image above for a larger version.

  Winter is never the best time for trying to persuade observers to look at galaxies as most deep sky observers are focusing their attention on the star clusters and nebulae of the Milky Way. There are however some galaxies to be found in unexpected places.

  The constellation of Cancer is perhaps best known for its two open clusters M44 and M67, but the third brightest deep sky object in this constellation is the galaxy NGC 2775.

  First discovered by William Herschel in 1783 NGC 2775 is a face on spiral galaxy of an unusual type. The core of the galaxy is very prominent and has a very smooth light distribution and unlike most spiral galaxies the arms seem to start from a long way out from the centre. The spiral arms themselves are very tightly wound and appear on images at least to be discontinuous with a large number of HII regions dotted along them. The spiral arms show a very curdled appearance on deep images.

  NGC 2775 is the largest galaxy in a small group which includes NGC 2773 and NGC 2777, both of which are very much fainter than NGC 2775. They were both discovered by Marth with Lassell’s 48" reflector, presumably from Malta. The NGC 2775 group is part of the larger Virgo cluster, much like our own Local group.

  With a blue magnitude of 11 the core of NGC 2775 should be visible with quite small telescopes, of the order of 10cm, however to see much detail in the spiral arms will require a telescope with a much larger aperture.

  Some sources suggest that NGC 2775 has been home to five supernovae in the last 30 year so it is obviously a good target for supernova hunters. I can however only find information on one in SN 1993z.

  NGC 2775 appears to be at a distance of about 17 Mpc. There are some suggestions that NGC 2775 maybe interacting with one of the smaller galaxies in the field from radio observations but this is not yet certain. NGC 2775 is also of interest because it does not seem to have a significant dark matter halo.

  Owen Brazell - Galaxy Section Director