Galaxy of the Month Archive 2024
In this series of articles we draw your attention to galaxies particularly worthly of an observer's time.
ACO 779 in Lynx
February 2024 - Galaxy of the Month
This month’s challenge is the galaxy cluster ACO 779 in Lynx. Containing at least 7 galaxies found in the NGC this should be a decent target for medium to large scopes.
The BCG (Brightest Cluster galaxy) is the giant elliptical galaxy NGC 2832, classified as a cD galaxy, also classified as E2, NGC 2832 itself was discovered by William Herschel in 1785. Most of the rest of the group appear to have been discovered by Stoney using Lord Rosse’s 72” at Birr. The Lord Rosse team found 12 galaxies in this area.
The group seems to contain mostly spirals and lenticulars with an interacting group from the extended VV catalogue in the centre. The same pair is also known as Arp 315, although this may apply to the three galaxies NGC 2830, NGC 2831 and NGC 2832. The galaxies in Arp 315 do not appear to be interacting.
ACO 779 is quite a small cluster with maybe 83 members and lies maybe 300 million light-years away. The Abell richness class however is 0 which suggests that there may be only 30 galaxies actually in the group. It covers roughly 50 arcminutes on the sky, although deep observations suggest it is more like 90 arcminutes, and lies roughly 40 arcminutes south of Alpha Lyn so it should not be that hard to find.
The group also contains a number of blue compact dwarf galaxies which appear to be forming stars at this time. There are some suggestions given its distance and location that ACO 779 may be part of the extended substructure of the Coma galaxy filament. There does appear to be some confusion regarding the NGC numbers in the group. NGC 2832 is certain but the others have been shuffled around a bit over time.
There is a decent amateur image of the group on Bernhard Hubl's website. I think observing this cluster will be best done with a chart as some of the fainter galaxies may look stellar. There is an interesting drawing available on X (Twitter) was made with a relatively small telescope, although this observers drawings appear to have some question marks about them.
A chart for the cluster can be found in Alvin Huey’s guide to observing Abell Clusters at which can be downloaded from his website. Steve Gottlieb suggests that NGC 2832 is visible in 13” but the others require a larger telescope, which given he usually observes in the high mountains suggests the group may require 45-50 cm to pick up more than the main galaxy. The Night Sky Observer's Guide (NSOG) Vol.1 suggests that a 20cm may show NGC 2832 and 30-35cm will show one of the others but 40-45cm are needed to show more galaxies in the group. The group is included in the Astronomical League’s groups and galaxy clusters program as well as in the SAC list of galaxy clusters.
Owen Brazell - Galaxy Section Director
If you'd like to try out the Clear Skies Observing Guides (CSOG), you can download observing guide for the current Galaxy of the Month without the need to register. CSOG are not associated with the Webb Deep-Sky Society but the work of Victor van Wulfen.
NGC 3414 in Leo Minor
January 2024 - Galaxy of the Month
Our galaxy this month is the lenticular galaxy NGC 3414 in Leo Minor. First discovered by William Herschel in 1785 it is the central galaxy of the rich galaxy group known as the NGC 3504 group, which in turn is also part of the Leo II group, a series of clusters on the edge of the Virgo cluster. The group is also catalogued as LGG 227, a cluster of 9 galaxies. For more information on the Leo II group see An Atlas of the Universe.
NGC 3414 is also known as Arp 162 and has a weak AGN of the LINER type. The Arp listing also includes NGC 3418, another nearby lenticular galaxy, although recent classifications suggest that this is a spiral galaxy. Interestingly the gas flows in NGC 3414 appear to follow a spiral pattern, however the gas in the inner part rotates in a different direction for the outer part. Deeper images also show signs of shells so all of this could be due to a recent merger. NGC 3414 also has a very strong bar in images.
NGC 3414 lies at a distance of perhaps 23 Mpc and NGC 3418 lies perhaps 800,000 lyrs from NGC 3414. If NGC 3414 is at this distance, then it is perhaps 40,000 light-years across, perhaps half the size of our Milky Way Galaxy. NGC 3414 is classified as S0pec.
It is probable that UGC 5958, a nearby edge on galaxy, is also associated with NGC 3414. Observations in the UV part of the spectrum with the GALEX satellite shows the bright core of NGC 3414 but also shows active regions in both NGC 3418 and UGC 5958 suggesting the galaxies are interacting. There also appear to be a number of dwarf spheroidal galaxies associated with NGC 3414, although these are far beyond amateur visual observations.
NGC 3414 is bright enough to make it into the Herschel 400 list of the Astronomical League. Observations from the UK suggest that NGC 3414 can be seen in 20cm but NGC 3418 is tough in a 40cm., however other observations suggest that NGC 3418 is visible in 30cm under very dark skies, although the quality of the site here was not defined. The The Night Sky Observer's Guide (NSOG) Vol. 2 suggests that 20-25cm telescopes will show NGC 3418 as a bright core but that 30-35cm is needed to show NGC 3818. Luginbuhl and Skiff (L&S) suggest that 25cm is needed to show NGC 3414 clearly and again it shows a bright core.
Owen Brazell - Galaxy Section Director