ASTRO: NGC 3945, 3975 and 3978

NGC 3945 is a double ring galaxy in Ursa Major just above the bowl of
the big dipper. It is about 65 million light-years distant (64 by
redshift). It is classed by NED as SB(rs)0+ with a LINER core. The NGC
project says more simply SB0. It reminds me of NGC 2859 I posted
February 2012. It too has a double ring structure but is seen a bit
more face on. I see a small fuzz blob on the east northeast outer edge
of the outer ring. NED shows nothing at its position. It is seen on
the POSS plates so is real. Is it the remains of something NGC 3945 is
digesting? I have no idea. A Hubble image of the galaxy's core shows
several dust clouds I wasn't able to resolve. An amateur's processing of
the HST data can be found at:
http://www.flickr.com/photos/7745218...0538/lightbox/ . The
galaxy lacks a central bulge. At one time it was thought such galaxies
didn't have a central supermassive black hole at their core but the HST
data says it likely has one, about twice the size of the one in our core
though the data is fuzzy enough it could also indicate no black hole but
that is of a low probability from how I read the papers. At 65 million
light-years the galaxy is about 120 thousand light-years across, about
the size of our galaxy if some current papers resizing the Milky Way are
correct.

There are two other NGC galaxies in the image. To capture them I had to
put NGC 3945 on the right side of the image. They are NGC 3975 and NGC
3978. They share almost the exact same redshift so are a true pair
though NGC 3975 is much smaller. Still NGC 3975 is rather large at 90
million light-years. So that makes 3978 enormous at over 250,000
light-years measuring the plumes. Just the arms gives a size of 190,000
light-years. Still a monster of a spiral galaxy. So where did the
plumes come from? I'd think NGC 3975 would be highly distorted if it
interacted with it but it looks pretty normal with no sign of plumes.
To complicate things NED shows two tiny galaxies against the disk of NGC
3978. If real and in the disk as NED seems to indicate then they could
be the remains of its latest meal of dwarf galaxies. That could account
for the plumes. Problem is they are right on fragments of spiral arms
and appear in my image as nothing more than star clouds similar to
several others seen along the arms. So are they galaxies that both
happened to align with arms or star clouds in the arms? I feel the
latter is most likely but have pointed them out in the annotated image
but with the notation G?

There are quite a few galaxies in the annotated image at about 135
million light-years. They are likely members of the Abell 1402 cluster
centered just below the lower right of my image. NED lists it at a
distance of 137.5 million light-years with a radius of 12.5 minutes
(about half the vertical size of my image) It is of group class 0 which
has 30 to 49 galaxies. Sufficient to take in most of the galaxies at
that distance in my image.

In the upper right corner is a very blue object. Some catalogs call it
a galaxy, others a galaxy with a very active AGN and still others say it
is a blue quasar. Not taking sides I've listed it as G/AGN/Q to cover
all three possibilities. Nearby are a trio of three galaxies (lower
right of the G/AGN/Q. While NED lists the faintest (upper left of the
three) the other two aren't in NED at all so get a question mark for a
label. No way to know if they are related or not unfortunately

Several galaxy clusters with a Big Cluster Galaxy at their core are
marked in the image, often at a distance that is closer than the
anchoring galaxy. Obviously they both can't be right. While the
anchoring galaxy is rather obvious in my image I don't see the other
members but I listed the count shown at NED anyway.

The blew blob on the very lower left edge of the image is due to the 8th
magnitude, A3 star, SAO 15664 hitting the very edge of the CCD. I
probably should have cloned it out but didn't think of that at the time.

14" LX200R @ f/10, L=4x10' RGB=2x10', STL-11000XM, Paramount ME

Rick
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