ASTRO: Arp 161

Arp 161/UGC 6665 is thought to be a merger of two spiral galaxies
located in western Virgo almost on he Leo border. It is about 270
million light-years distant. Arp put it in his class of galaxies with
diffuse elements. An obvious reference to its cone shaped jet/plume.
Arp's comment "Faint, diffuse material extends away from neck."
Several sources seem to see the bright region at the "neck" as Arp calls
it, as a jet with the plume extending from it. While the night I took
this was awful with resolution of only about 3.5" of arc or worse, the
"jet" is really two point sources, better seen in the Sloan image. Also
better seen in the Sloan image is the spiral structure of the galaxy.
It was blurred out of existence by the horrid seeing I experienced the
night I took my image. The plume appears the result of the merger and
there is no "jet". The lower of the two star-like objects is shown at
NED to be a 20th magnitude star on the Sloan survey. The upper,
brighter object isn't listed at NED. Likely, it too is just a star in
our galaxy confounding the issue. Arp had even worse seeing than I did
so his image is of even less help here. Odd to out resolve the 200"
scope when I'm having a bad night. Arp must have been desperate that
night. I know the feeling.

NED classes the galaxy as Sb pec;HII;WR Sbrst. The starburst is likely
due to the merger. I don't know what NED means by "WR". Usually that
refers to a Wolf-Rayet star. Anyone know what it means in the case of
galaxy classification? NED's own reference page fails to define the
term. All I can think of is the spectra has features of Wolf-Rayet
stars. A starburst galaxy, like Arp 161, would likely have a strong
population of such stars.

Near the bottom edge, left of center, is CGCG 012-064. It has the same
redshift as Arp 161 so likely part of its local group.

The annotated image shows a galaxy cluster, SDSS CE
J175.616547+00.441206 northeast of Arp 161 at 3.5 billion light-years.
NED shows it with 24 members in a circle 3.8 minutes across. The center
of the label marks the center of the cluster. No galaxy marked that
point that I could see or NED mentions. One at that distance is seen
however it isn't marked in NED as a bright core or cD galaxy. Still it
is likely a member of the cluster. Another cluster, MaxBCG
J175.68388+00.38916, at 3.2 billion light-years is also northeast of Arp
161. It has 17 galaxies but no size was listed. A bright core galaxy
is shown at the same position but without a distance estimate. I show
it as GC/G with the galaxy distance a question mark. I'm not done yet!
A third galaxy cluster at 3.2 billion light years, SDSS CE
J175.678543+00.482395 is further northeast. It has no galaxy a its core
though a red one is just right of the core with the label for it to its
immediate left. The cluster is listed as 1.6 minutes in diameter
containing 23 galaxies. Don't think we are done with galaxy clusters in
this image. Mostly east from Arp 161 is the galaxy cluster SDSS CE
J175.833755+00.375661 at 3.9 billion light-years. It is 3.6 minutes in
diameter with 23 members, one of which has a red shift value of 4.0
billion light-years. I used one label for both though they aren't at
the same position. The center of the cluster is behind the glare of a
bright star while the galaxy, and a second one without a redshift
measurement are just southeast of the star's glare circle.

Southwest of Arp 161 is a trio of objects. The most obvious a rather
large galaxy, MGC 0023433/MGC 0096273 at 1.2 billion light-years. Why
it has two designations I don't know. Above it is the Ultraviolet
Excess Source, SDSS J114150.08+001314.3. At least that's how the Sloan
survey categorizes it. The MGC calls it just a star as does the 2QZ.
But with a measured redshift that puts it 9.5 billion light-years away
it sounds more like a quasar to me. There appears to be a possible
tidal tail coming from the galaxy. Apparently it is the separate galaxy
SDSS J114150.87+001307.4 with an unknown redshift. Several other UvES
objects with large redshifts are also identified in the image. I assume
they are all quasar like objects. I suppose it is possible they are
extreme starburst galaxies but that these distances I find that unlikely.

Also to the northeast is a quasar, SDSS J114239.34+002640.4. While NED
puts its redshift at z=1.872 for a distance of about 10.2 billion
light-years one source, the 2QZ catalog gives a z of only 0.103 for a
distance of about 1.3 billion light-years. This doesn't seem reasonable
to me, especially for a 20.5 magnitude quasar so I went with the value
NED prefers.

Arp's image:
http://nedwww.ipac.caltech.edu/level...ig_arp161.jpeg

14" LX200R @ f/10, L=4x10 RGB=2x10x3, STL-11000XM, Paramount ME

Rick
--
Correct domain name is arvig and it is net not com. Prefix is correct.
Third character is a zero rather than a capital "Oh".

Odd, the Sloan image didn't get through. Trying again.

Rick
--
Correct domain name is arvig and it is net not com. Prefix is correct.
Third character is a zero rather than a capital "Oh".