Galaxy of the Month Archive 2017
In this series of articles we draw your attention to galaxies particularly worthly of an observer's time.
March 2017 - Galaxy of the Month
IC 504 Group in Hydra
Over time the Galaxy of the Month selection has varied in terms of the challenges presented from objects visible in small telescopes to ones requiring the use of the larger sized ones in amateur hands. For this month’s selection, the choice is an intriguing one in terms of how difficult they will be to see.
The small group of galaxies around IC 504, which are IC 504, IC 505 and IC 506, were first discovered by Lewis Swift in 1888 using a 16” refractor in Rochester NY. This was perhaps not the greatest site even then. The galaxies were described by him as faint however the brighter pair should perhaps be visible in a modern 15-16” telescope.
The galaxies are always going to be challenging ones to observe for northern observers as they lie in the head of Hydra and therefore will never rise that high, even at their best.
These galaxies maybe physically associated and are listed in the WBL catalogue as a group of seven galaxies. The group is numbered WBL 179. I assume the other cluster members are the CGCG galaxies in the field.
IC 504 and IC 505 are classified as lenticular galaxies in some sources and IC 506 appears to be an elliptical galaxy. Deep images from the SDSS and PanSTARRS surveys however show that IC 504 appears to have spiral arms, or at least a ring of new star formation, so perhaps it is not a lenticular but a spiral galaxy. Interestingly NED also gives the classification for IC 505 as S (spiral), which suggests some confusion, although it could of course be S0. It is also suggested that IC 505 may be a binary AGN.
Despite being visually fainter than IC 504 it appears that IC 505 is also classified as the BCG galaxy (brightest cluster galaxy) for this group. As the SDSS image does not show any sign of spiral arms for IC 505 it appears that galaxy morphology classification is still as much as an art as much as a science.
The field is full of much fainter galaxies when viewed on the SDSS and of particular interest is the horseshoe shaped string between IC 504 and CGCG 32-9. I doubt that any of these will be seen visually although CGCG 32-12 (MCG +1-22-7) might be with larger telescopes. There are no visual observations of this group that I have been able to find which suggests that they are well off the beaten track. Perhaps not surprisingly there is not much information on these galaxies but the suggested distance is perhaps 60 Mpc.
For those not familiar with the PanSTARRS survey the image data is now available. Note that you cannot control the field you get and the data is not as good as the SDSS.
Owen Brazell - Galaxy Section Director
February 2017 - Galaxy of the Month
NGC 3801 Group in Leo
Writing the galaxy of the month article is always a challenge, especially coming up with new targets so I am grateful this month for the suggestion from Andrew Robertson to have the small group of galaxies associated with NGC 3801 as the challenge.
The group has quite a chequered discovery history, and the usual naming challenges. The brightest galaxy in the group is NGC 3801 and it was discovered by William Herschel, along with NGC 3790. Even the NGC sleuths seem to disagree about who discovered NGC 3806. This could have been either William Herschel or, more probably, John Herschel.
Although NGC 3806 was bright enough to be seen by William at the time he was using his 18.7” reflector in Newtonian mode rather than in front view mode and Wolfgang Steinicke suggests the extra light loss may have contributed to him not seeing it.
Some confusion has also reined over NGC 3806 being numbered as NGC 3807 but this is actually a star seen by the team at Birr. They did however discover the other two galaxies in the field, NGC 3802 and NGC 3803. Some software, for instance Megastar 5, still plots NGC 3806 as NGC 3807.
The group is regarded as a physical system, or at least some of them are, and have been given the designation WBL 347, which lists 5 galaxies in the group. The group is also in the LGG catalogue as number 246, which lists 17 galaxies in the group, an interesting discrepancy. If this is true it would mean that this little group of galaxies covers over 3 degrees on the sky as the LGG survey also includes NGC 3800 and 3853 along with NGC 3768 as part of the group.
NGC 3801 is classified as a S0 (lenticular galaxy) but as the attached Hubble image shows it has some very strange dust clouds in it which would be unusual for a S0 galaxy including one at right angles to the main axis.
All of this suggests some form of interaction/merger, indeed in the UV NGC 3801 shows an intriguing S shape which suggests the merger hypothesis is the more likely. This is also borne out by looking closely at the SDSS image which shows evidence for shells or streams about the galaxy. It also has a radio jet and this is suggestive of an AGN.
The SkyTools chart attached also does not mark NGC 3803, it is the fuzzy galaxy above NGC 3802. It is regarded as too faint to mark at this scale.
Most of the galaxies here are regarded as lenticulars except for NGC 3806 which is a face on spiral.
Interestingly none of these galaxies appear in Night Sky Observers' Guide (NSOG) or other popular resources, although it is in the AL Galaxy groups and clusters list.
Owen Brazell - Galaxy Section Director
We've received some excellent observations of this group of galaxies already!
January 2017 - Galaxy of the Month
NGC 2289 Group in Gemini
Winter is never an easy time to select galaxies for the GOM column as we are mostly looking into the Milky Way areas. There are however a number of galaxies near the head of Gemini and this month’s challenge is the small group of galaxies around NGC 2289.
The group appears to be a physical one and is listed as WBL 126, which consists of the five galaxies NGC 2288, 2289, 2290, 2291 and 2294. Unfortunately this is a pretty faint group and as such will be a challenge for larger telescopes and will probably require telescopes in the region of 37cm aperture plus to see visually.
William Herschel discovered NGC 2289 and NGC 2290 with his 18.7” reflector in the spring of 1793 but the other three galaxies in the group were found by George Stoney using Lord Rosse’s 72” reflector at Birr when following up nebulae discovered by the Herschels. Some sources suggest that NGC 2291 was discovered by John Herschel but this is almost certainly an error and he only saw the two galaxies his father saw. NGC 2290 may be the brightest galaxy in the group.
The group were photographed early on by Francis Pease using the 60” reflector at Mt Wilson in 1920. In his paper
Photographs of Nebulae with the 60-inch Reflector, 1917–1919he interestingly thinks they are all spirals. Of course at this time it was still unknown whether the nebulae were inside our own galaxy. Hubble’s observations were still a few years in the future.
The group is fairly tightly concentrated and all the galaxies will fit in the field of a high power, 300x, eyepiece. The group consists of three lenticulars, one spiral and an unknown type (NGC 2288, although possibly this is an E5). My suspicions are that NGC 2288 is going to be the most challenging of the galaxies to see.
The distance to the group appears to be about 70 Mpc distant. There is some galactic extinction in this area which could be a contributing factor in the faintness of these galaxies as they don’t lie completely outside the Milky Way. I was surprised to find that, despite its faintness, the group is part of the Astronomical League's Galaxy group and clusters observing program.
Perhaps not surprisingly given the groups faintness there have been few studies made of the group apart from statistical ones to show it is a group. Given its faintness it is perhaps no surprise that it does not appear in the Night Sky Observer's Guide (NSOG) but Steve Gottlieb has observed all the galaxies in this group and his observations can be found on his website.
Owen Brazell - Galaxy Section Director