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

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.

Attachment 3811

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

Owen

I have looked at a number of these galaxies. I first looked at NGC 3998 with my 10 inch skywatcher back in 2011 and noted it as a faint circular galaxy near to NGC 3990 which was oval in shape.

In 2016 NGC 3998 is noted in my records as a very bright circular object in my 16 inch dob. I was also able to pick up NGC 3990 again but also now NGC 3972 which required averted vision to see the slither and NGC 3982 which was a bright oval.

I must go back again with my 20 inch scope!

Thanks for sharing all the details of the group.

Mark

Excellent field.

I have this from March 2010, 4" (yes) F/5.5, 8-24 mm ocular, Bortle 3 site on a night of very good transparency: "NGC 3990 (II.791, m12.6, companion of NGC 3998, a Herschel class I object) is seen, as is NGC 3972 (II.789, m12.3)." 3998 was the original target of that observation, and was seen.

Fast forward to March 2016, and I recorded (20" F/5, 13 mm ocular, SQM 21.2 - club observatory): "NGC 3972, 3977, and 3982. -72 and -82 are Mahtessian 170 members, -77 far in the background. Just framed by Ethos. -82 bright, -72 lens-shaped, -77 small, round." NGC 3990 was also reobserved.

Nice write up Owen! Please note that the first sentence mentions NGC 3970 but this should be NGC 3977 (NGC 3970 is a galaxy in Crater). Here are my observations with my 20" dob:

NGC 3972: At 320x a thin needle with a bright core.
NGC 3977: At 320x a small, round, faint glow without a clear core.
NGC 3982: At 320x a bright, typically elliptical galaxy. Smaller and fainter than close by NGC 3998.
NGC 3990: At 320x a small, faint oval glow with a slightly brighter core.
NGC 3998: At 320x a bright, typically elliptical galaxy. Larger and brighter than close by NGC 3982.

NGC 3631: At 320x a large, round glow with a slightly brighter center and very faint hints of spiral structure.
NGC 3718: At 320x a large, faint glow with a moderately bright central region. The galaxy is S shaped. I didn't know what to expect and I am surprised by yhe beauty of it.
NGC 3729: At 320x a compact galaxy with a bright, elongated core with a bright star at one side. An oval starts at one end of the elongated core and runs all the way around the galaxy.
NGC 3657: Not seen yet.
NGC 3913: Not seen yet.

Thanks Wouter - typo's everywhere :-(

I don't think I can edit the original post to correct in there.

Quote:

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Originally Posted by obrazell

Thanks Wouter - typo's everywhere :-(

I don't think I can edit the original post to correct in there.

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Yes, your post can be edited, at least I can edit mine. If not, Dragan can do it for you...

Quote:

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Originally Posted by Paul Alsing

Yes, your post can be edited, at least I can edit mine. If not, Dragan can do it for you...

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Paul's correct. Bottom right corner of your original post you should see a button for "edit post". Click on that and off you go!

cool - done it.

Just tried the tidal tail of NGC 3990 and it was clearly visible with the 27-inch under very good transparency and NELM around 6m5+. Later I can add a sketch of the pair NGC 3990/3998.

Owen, below I add the given later sketch of NGC 3990/3998.

27", 172x, NELM 6m5+, Seeing IV
Attachment 3830

Hi Owen,

What a nice group of galaxies. I observed them with my 12" Dobsonian this week, scanning the field at 168x magnification.
I like how different they look from each other.
NGC 3998 very large and bright with a well-defined edge
NGC 3990 smaller but pretty bright
NGC 3977 seems to have a lower surface brightness than NGC 3998.
NGC 3972 almost edge-on with a bright core
NGC 3982 with a bright core, but diffuse outer region.
Additionally, I found two faint galaxies:
UGC 6919 elongated faint smudge
PGC 2505536 small and diffuse smudge visible most of the time at averted vision. It is a background galaxy 1.1 billion light years away from us.

Please find attached my sketch.

Clear skies,

Robin

Attachment 3852