UGC 4671 and NGC 2692

UGC 4671 and NGC 2692 are a pair of very different galaxies in
northwestern Ursa Major just above its front paws. Redshift puts them
about 190 million light-years distant. UGC 4671 is classed simply as S?
while its much redder companion is listed as SBab:. NGC 2692 being a
rather normal red barred spiral with little to no recent star formation
is a rather dull partner but nice color contrast to the far more
interesting UGC 4671. This is a tight blue spiral in the center
surrounded by a large, disk with only hints of spiral structure. While
NED lists several galaxies seen right through this disk it omits the
most interesting one. The others are very small and star-like but the
one NED omits appears to be a distant, near edge on spiral. It has a
normal left (east) side and a reddish core but is missing most of the
western (right) side. I doubt that it is really missing. Just that it
is behind UGC 4671 and the western half of the galaxy is mostly obscured
by dust and gas in the denser core region of UGC 4671.

Oddly the literature has little to say on this. The only paper I found
with anything on it was published in 1997 and says: "If the sharp linear
feature in UGC 4671 is of tidal origin it is difficult to see how it
connects with the main galaxy. Further apart from this feature there are
only modest signs of disturbance of the H I disk of UGC 4671. The
feature is hence probably best explained as an edge on dwarf galaxy seen
in projection against the disk of UGC 4671. Note that the velocity field
in the region of this feature is consistent with this interpretation."
To me the galaxy appears normal size, not a dwarf. I can't tell for
sure but the paper sounds a bit like it is assuming the galaxy is in
front of UGC 4671. That would explain calling it a dwarf. Maybe the
illusion of an off center core for it added to the problem. The photo
in the paper really doesn't resolve the core as it looses it in the
glare of the center region of UGC 4671. I do wish UGC 4671 were closer
as it looks like it has a lot of fascinating detail just asking for a
better view.

I found nothing indicating UGC 4671 and NGC 2692 were interacting. The
large, low luminosity disk of UGC 4671 shows some hints of plumes and
tidal distortions at the edges, especially on the eastern side. This
could be from it digesting a small companion in the past. Otherwise I
don't see much around it that could have interacted with it long ago.

The annotated image has something to annotate for a change. As usual,
distance in billions of light-years based on NED's 5 years WMAP
calculator is shown after the object designation. Larger objects are
noted by catalog name while the rest are noted by type, G for galaxy, GC
for galaxy cluster, Q for quasar and UvES for quasar candidates. All
that NED has redshift data for are noted. A p after the distance
indicates it was determined photographically by how its intensity varies
in different filters rather than spectroscopically. This isn't quite as
accurate but usually in the ballpark. The location of galaxy clusters
is noted at the position of the big cluster galaxy that anchors the
cluster. The difference in distance estimates is likely due to that of
the cluster being made photographically while the galaxy is usually done
spectroscopically. I suspect the big cluster galaxies distance estimate
is the more accurate one.

One fuzzy galaxy southeast of NGC 2692 is not in NED at all. This
happens rather regularly. It and another faint fuzzy galaxy to its
southeast appear likely nearby low luminosity dwarf galaxies. While the
latter is in NED it has nothing on it to settle the issue however.

14" LX200R @ f/10, L=5x10' RGB=2x10', STL-11000XM, Paramount ME

Rick
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