ASTRO: Arp 21 -- Blue among the gold

Arp 21 is located in eastern Leo Minor a bit over 400 million
light-years distant. It falls into Arp's class: Spiral Galaxies; 3
armed. That much seems fairly certain. Things get rather fuzzy beyond
this. For instance where's the third arm? I really don't see a
definite third arm in his image, my image or the Sloan image. Is it the
fuzzy detached spur running parallel to the arm wrapping around the
bottom of the core ending to the north by a round object? Or is the the
odd looping feature east of the south going arm that is strangely drawn
out ending in a sudden backwards "j" shape? Arp made no comment on this
one. NED does say it is a three armed spiral. It just classes it as a
spiral however.

Now about that "round object" northeast of the core. The SDSS has two
entries for it. One calls it a star while the other says it is a galaxy
with a red shift also about 400 million light-years distant. Arp 21 is
in the Vorontsov-Velyaminov Interacting Galaxies catalog as VV552b.
That would indicate they too considered that object a galaxy. Now about
that "b"; where's VV552a you ask? Nearly 4 hours west and 17 degrees
north! Confusing isn't it? VV552? It apparently doesn't exist. The
catalog has no separate entry for the round object. I used the galaxy
designation and distance in my annotated image.

Arp 21 was picked up by IRAS so is a strong IR emitting galaxy
indicating a lot of star formation is going on hidden behind dust warmed
by the stars it hides. This makes it likely the galaxy did encounter
another in the recent past. It might be the round object or one of the
other galaxies in the area.

Looking around the area, even in the limited field of the cropped,
enlarged image, there's a lot of distorted galaxies. Near the right
edge of the cropped image is a red spiral that has a faint plume going
north. In the lower left corner is a ring galaxy much like M94 with its
very faint outer ring. Both would seem to be due to long ago
encounters. There's an obvious pair of red elliptical interacting
galaxies northeast of Arp 21. At the top are two, very blue,
interacting galaxies. They have one entry in a rather obscure catalog,
MAPS-NGP O_318_0293285. That stands for Minnesota Automated Plate
Scanner - North Galactic Pole. Minnesota and North Pole describe my
winter perfectly. Looking around the full image will turn up others.
This is a very interesting field. Unfortunately I found virtually no
papers on any of the objects, including Arp 21. Seems oddly ignored in
the literature.

I've included the SDSS image of this galaxy.

Arp's image
http://nedwww.ipac.caltech.edu/level...big_arp21.jpeg

14" LX200R @ f/10, L=4x10' RGB=2x10'x3, 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".

Rick,

the detail you got in these tiny galaxies is really amazing.

Stefan

"Rick Johnson" schrieb im Newsbeitrag
ter.com...
Arp 21 is located in eastern Leo Minor a bit over 400 million
light-years distant. It falls into Arp's class: Spiral Galaxies; 3
armed. That much seems fairly certain. Things get rather fuzzy beyond
this. For instance where's the third arm? I really don't see a
definite third arm in his image, my image or the Sloan image. Is it the
fuzzy detached spur running parallel to the arm wrapping around the
bottom of the core ending to the north by a round object? Or is the the
odd looping feature east of the south going arm that is strangely drawn
out ending in a sudden backwards "j" shape? Arp made no comment on this
one. NED does say it is a three armed spiral. It just classes it as a
spiral however.

Now about that "round object" northeast of the core. The SDSS has two
entries for it. One calls it a star while the other says it is a galaxy
with a red shift also about 400 million light-years distant. Arp 21 is
in the Vorontsov-Velyaminov Interacting Galaxies catalog as VV552b.
That would indicate they too considered that object a galaxy. Now about
that "b"; where's VV552a you ask? Nearly 4 hours west and 17 degrees
north! Confusing isn't it? VV552? It apparently doesn't exist. The
catalog has no separate entry for the round object. I used the galaxy
designation and distance in my annotated image.

Arp 21 was picked up by IRAS so is a strong IR emitting galaxy
indicating a lot of star formation is going on hidden behind dust warmed
by the stars it hides. This makes it likely the galaxy did encounter
another in the recent past. It might be the round object or one of the
other galaxies in the area.

Looking around the area, even in the limited field of the cropped,
enlarged image, there's a lot of distorted galaxies. Near the right
edge of the cropped image is a red spiral that has a faint plume going
north. In the lower left corner is a ring galaxy much like M94 with its
very faint outer ring. Both would seem to be due to long ago
encounters. There's an obvious pair of red elliptical interacting
galaxies northeast of Arp 21. At the top are two, very blue,
interacting galaxies. They have one entry in a rather obscure catalog,
MAPS-NGP O_318_0293285. That stands for Minnesota Automated Plate
Scanner - North Galactic Pole. Minnesota and North Pole describe my
winter perfectly. Looking around the full image will turn up others.
This is a very interesting field. Unfortunately I found virtually no
papers on any of the objects, including Arp 21. Seems oddly ignored in
the literature.

I've included the SDSS image of this galaxy.

Arp's image
http://nedwww.ipac.caltech.edu/level...big_arp21.jpeg

14" LX200R @ f/10, L=4x10' RGB=2x10'x3, 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".