Object of the Week March 8th, 2020 - NGC 3998 and friends

[obrazell]

NGC 3998

Galaxy

Type SA(r)0
R.A.: 11h57m56.2s
Dec.: +55°27'13" (2000)
Magnitude: 11.40 B
Size: 2.8'x 2.2'
Const: UMa

NGC 3998 is involved with a group of 5 NGC galaxies (3972, 3997, 3982 and 3990) that were all discovered by
William Herschel in April 1789. Lewis Swift independently rediscovered NGC 3977 and Dreyer included it in the
NGC as NGC 3980 so there may be some confusion in places as to what it is called. NGC 3998 Is also involved
with the galaxy group LGG 241 which includes NGC 3772 but none of the other NGC galaxies in the field. It does
however include NGC’s 3631, 3718, 3729, 3913 and 3657. The LGG 241 group consists of perhaps 10 galaxies.
Distances estimates to NGC 3998 vary widely from 14Mpc to 30Mpc but the most recent cluster around the lower
end at around 14 Mpc. It has also been suggested that NGC 3998 is part of the UMa Cluster, a spiral rich
subgroup of the Virgo Cluster, although lying somewhat further away from us than the main core of the Virgo cluster.
In this case it would be part of the NGC 3992 subgroup of the UMa cluster. NGC 3998 itself is a lenticular galaxy
but it is also classified as a Seyfert, which appears odd as lenticulars don’t normally come with the gas and
dust content which is what normally fuels Seyfert activity. Recent classifications however have it at the
lower end of the AGN spectrum as a LINER. It also appears to have a low dark matter content. NGC 3990 also
appears to be a S0 galaxy as well seen edge on. NGC 3977 is a face on spiral and NGC 3972 is a rather nice near
edge on spiral galaxy. There are a number of other faint galaxies in this field that will be visible with larger
telescopes including MCG +9-20-41 and many MAC galaxies. The whole field of galaxies is such that it should fit
in the same field in a modern hyperwide eyepiece with a power of perhaps 180x. judicious placement of the
centre of the field will also allow NGC 3982 to appear with the group. NGC 3982 is another face on spiral with
a very bright core. There is a nice Hubble image of NGC 3972 at
https://www.nasa.gov/image-feature/g...ic-lighthouses.
NGC 3972 appears to be part of a non-interacting pair of galaxies with NGC 3977.

ngc3998_SDSS.jpg

As always giove it a go and let us know what you see.