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ASTRO: Arp 280
Arp 280/NGC 3769 is a pair of probably interacting galaxies in Ursa
Major at a distance of 50 million light-years. Red shift puts it a bit
closer at 44. It is a member of the Ursa Major Cloud of galaxies which
are thought to range about 50 to 55 million light-years distant and
includes M108 and M109 as its most famous members. Arp put it in his
class of interacting double galaxies. This one is within easy reach of
an 8" telescope from dark skies at a visual magnitude of 11.7.
Note the knot in the western (right) member. Everything I saw on this
pair refers to it as a knot, including the Kanipe-Webb book on the Arp
Atlas. But in my color image it came out with a orange core and blue
outer parts as if it were a separate galaxy. Knots are almost always
blue. If red then its H alpha red due to large clouds of ionized
Hydrogen in them. This got me searching further. I found a Hubble
image (attached) that shows it clearly is a separate barred spiral
galaxy. NED doesn't include it either as part of a galaxy or as a
separate galaxy. Is it a distant galaxy or a dwarf spiral being
digested by Arp 280? It's arms are distorted but I still think it more
likely a background galaxy. It wouldn't take much to change my mind
The western member is by far the larger and is classed as SB(r)b:. The
NGC project has it as Sb. Considering it appears to have an obvious bar
I am a bit puzzled by the NGC project's classification. The eastern
member is classed SBm Pec by NED. Looks more like a blog with a few
knots to me. The eastern blue blob (pair actually) carries its own
designation in the Sloan survey as SDSS J113751.49+475250.1. It is
labeled "part of galaxy" and not a separate galaxy. It's red shift puts
the knot at 48 million light-years. Pretty much in line with the
distance to the Ursa Major cloud even though the red shift for the
galaxy itself says 44 million light-years.
In the southwest corner of the image is the galaxy cluster MaxBCG
J174.22470+47.81605 at 3.1 billion light-years with 32 members. The
diameter isn't listed however. Is the red galaxy at 3.1 billion
Light-years that is well east (left) of Arp 280 a member? If so it is
The large galaxy west of this cluster at a distance of about 470 million
light-years is UGC 06576, an SB0 galaxy with a very large faint outer
disk. It appears to have a small companion to its southwest at about
the same distance.
A couple very blue quasars are in the image. In processing it I
couldn't help but notice a super blue starlike object east of Arp 280.
I was sure it would be a quasar when I went to look it up but nope. It
is listed as a white dwarf and X-ray source in the ROSAT catalog All-Sky
Survey Bright Source Catalog of X-ray sources, 1RXS J113836.9+475459.
That's one hot white dwarf. So where is its planetary nebula? Has it
already dissipated? It is labeled as WD/X in the annotated image.
After writing this I found limited data on the western part of this
galaxy pair at the Hubble Legacy site. I did a quick enhancement of the
mono data there. It supports the idea the blob at the north end of NGC
3769 is indeed a separate galaxy.
14" LX200R @ f/10, L=4x10' RGB=2X10'X3, STL-11000XM, Paramount ME
Correct domain name is arvig and it is net not com. Prefix is correct.
Third character is a zero rather than a capital "Oh".
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