see also
http://adsabs.harvard.edu/abs/2007ApJ...662..304B


On Thu, 14 Oct 2010 02:34:43 -0500, Rick Johnson
wrote:

Arp 10 is in Arp's category Spiral galaxies: Split arm. It is located
in Cetus about 400 million light years distant. While it appears to
have a companion just to the north that galaxy, 2MASX J02182874+0540079,
is over 700 million light years further away (1.15 billion total). But
it apparently does have a companion. To me it looks like a star, even
on the SDSS image. It is the starlike object right beside the core to
the southwest (lower right). It is identified in NED as: ARP
010:[BMV2007] Companion with a red shift that puts it about 420 million
light years away. Arp's comment, "Nucleus off center in ring." I can't
say I see the "split arm" that caused Arp to put it in that category.
Is it the ring that is more a slight oval coil that doesn't quite
overlap? Is it the faint arms at the southeast that seem to go in
opposite directions? Or is it something else? Arp doesn't explain.

While NED lists the starlike object near the core of Arp 10 as a
companion it gives it the classification of Sab? How you get that out
of a starlike object is beyond me. NED classes Arp 10 itself as only
S?. Looks like a barred spiral with a ring to me. To add to the
confusion one paper wonders if the brightest blob in the very blue arc
in the northwest part of the galaxy is the core of a second galaxy. In
other words this object is still very much a mystery with all sorts of
contrary information that has me going in circles. While not all the
papers agree, to me this looks at least like a near head on collision of
two galaxies. If that starlike object is the core of the "bullet"
galaxy it apparently lost most of its stars in the process and is now
just a core. This could explain the apparent clockwise and counter
clockwise shape of the faint arms on the southeast side of the galaxy's
disk. Being so face on it may be difficult to tell if the stars really
are orbiting in opposite direction. I found nothing indicating any
measurements have been done. I'd expect radio telescopes to be best for
this chore. One note at NED has this to say about this system:

"Faint "ripples" are seen at very faint levels around the galaxy. These
ripples complicate the simple interpretation of Arp 10 as a collisional
ring. Recent H I observations by Charmandaris & Appleton(1996) show that
the bright inner ring is surrounded by an H I disk which extends beyond
the faint "ripples." Although not as simple as ring galaxies like VII Zw
466, Charmandaris and Appleton suggest that the process that formed the
rings and shells involved a central collision between a gas-poor early
type galaxy and a large-type H I rich disk."

The full article is available for those with good hip waders at:
http://articles.adsabs.harvard.edu/c... iletype=.pdf

The field's data has not yet been entered into NED's data base even
though the field has been imaged by the SDSS. So there's little
information on the rest of the field. In fact I've already covered all
objects with a known red shift in NED's database. Normally I'd not
prepare an annotated image for such a weak field but there's an asteroid
that was caught right as it went from normal to retrograde motion. It
appears as a faint star with no trail visible as it moved only a bit
over one arc second during the exposure. It is 2004 FD41 at magnitude
20.6. So it won't be obvious without it being pointed out. The other
asteroid (8604) Vanier is very easy to spot at magnitude 16.8 to the
right of Arp 10. It is so bright it even shows in the color filtered
images making a short blue green and red trail before the white trail
from the luminosity image. It is moving in normal eastward motion
rather than retrograde as most asteroids I pick up earlier in the
evening do.

Without any distance indicators I've marked all galaxies with their
catalog entry instead. There are so few cataloged I'm listing every one
known to NED along with the red shift distances to the three main ones.
There is one galaxy cluster in the image. A line goes to the
approximate center identified in NED. No size or galaxy count is given,
nor distance of course. I do see lots of faint fuzzies in the area but
nothing out of the ordinary except for a small concentration to the NW
of that position containing very faint small fuzzies. Enlarge the image
for a better view.

While the Hubble Space Telescope imaged quite a few galaxy collisions
this wasn't one of them.

Arp's image:
http://nedwww.ipac.caltech.edu/level...big_arp10.jpeg

14" LX200R @ f/10, L=4x10' RGB=2x10'x3, STL-11000XM, Paramount ME

Attached, full image, enlarged 2x crop, annotated and SDSS image

Rick