ASTRO: Arp 57

Arp 57 is in the southeast corner of Coma Berenices just a few minutes
of arc across the border from Virgo. The bottom of the image is in
Virgo in fact. It is about 813 million light years away. Arp put it in
his category of spirals with high surface brightness companions on its
arm. This time finding the galaxy on the arm is easy as his comment
reads: "Small companion connected to end of arm." Or is it easy. Seems
there are two galaxies on the end of the arm, a small round blue one
followed a bit further out by a larger red oval one. To add to the
confusion there's a third one just west of the core of the main galaxy.
All are marked on the annotated image. The problem is there's no red
shift distance for the two on the end of the arm. The third one no one
seems to mention is at the same distance and far closer to the core, at
least by line of sight. Or is it just a knot in the spiral arm and not
a true galaxy? Then there's the more distant companion also at about
the same distance. It doesn't appear distorted so likely hasn't
interacted with Arp 57 though obviously is nearby. The two "on" the arm
may be as well, I just can't tell. NED makes no attempt to classify any
galaxy in the image even the obvious ones.

Coverage of this field at NED is hit or miss it appears. In the upper
left area of the image three rather bright galaxies aren't in their data
base. But below the topmost of the three is a 22.4 magnitude galaxy
I've marked that is. Also below these three is a large group of very
faint galaxies mostly 22nd and 23rd magnitude. Those I checked are in
NED. They appear to be an obvious cluster but NED lists none in this
area. Nor does it list a redshift for any in the group -- very
frustrating.

A bit above and right of this area is an object at 3.4 billion
light-years that is listed in NED as both a Seyfert 1 galaxy and a
quasar. Its PSF does fit a point source so likely is a rather close quasar.

This image was taken on a night of far better seeing than normal so was
binned 1x1 for a 0.5" per pixel image scale. I didn't shrink it to
match the Sloan image.

Arp's image
http://nedwww.ipac.caltech.edu/level...big_arp57.jpeg

14" LX200R @ f/10, L=8x10'x1 RGB=2x10', 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".