ASTRO: Arp 319 aka Stephan's Quintet reprocessed

I originally did this one in mono in 2006 and got some poor color data
in 2008. Not having proper software mating the two was a nightmare as
I'd made changes in my system and changed the image scale slightly.
Just recently I found I'd retaken the color data only weeks later after
the first try but under far better conditions. Now I have the software
needed to auto scale the two to match and better software for processing
the luminance channel. It still could use more luminance. Still this
is so much better than the 2008 try and uses color data that sat lost on
the hard drive for 5 years (well a different hard drive actually since
it was so old), It pretty well amounts to a new image. Much of the
first paragraph below is from back in 2006 and 2008 however.

Stephan's quintet is really a group of 4 galaxies with a 5th galaxy in
the foreground. Though it is much smaller so appears about the same
size as the others. The fake is NGC 7320. it is apparently the largest
of the group and the bluest. It is really a member of the so called
"Deer Lick" group located less than a degree away. It is located only
some 40 million light years away while the other 4 are about 270 million
light years from us. At one time this group was put forth by some to
disprove red shift as a distance measure to the universe. Since NGC
7320 is close it has a small redshift while the other 4 have a large
redshift. But if all were at the same distance then redshift was called
into question. It took Hubble to answer this for sure. It could
resolve stars in NGC 7320 but only massive star clusters in the others.
This was consistent with the redshift distances and it is now accepted
that 7320 is a Deer Lick member seen in front of the far more distant
group. Actually we do have 5 members of this distant group. To the
left a bit is a bared spiral whose arms make a nice ring, NGC 7320C.It
is now known to be a member of the group and may be responsible for some
of the tidal plumes. So there really are 5 galaxies in Stephan's
quintet, just that one isn't the one we thought was a member for many years.

For a shot taken with a far larger telescope on Kitt Peak than mine see:
http://www.noao.edu/image_gallery/html/im0414.html

Actually there are several more members of the group. Just that like
7320 is well away from its group these other members aren't as close by.
One is LEDA 141041 even further east than the first 5. Then there's
the very awkwardly named [WYV2002] 6 in the upper left corner of the
image. Just out of the image due east of the cluster is NGC 7320B yet
another member of the group. These are the only ones I found with
redshift values to show they are very likely group members. In the
lower part of the image is NGC 7320A which looks almost a twin of NGC
7320B I missed catching. Both these last two are members of the 2MASS
flat galaxy catalog. On the west side of the image is the S0 looking
galaxy PGC 69218. It too has no red shift data but could possibly be a
member of the group.

I find it interesting that while NGC 7320 is now known not to be a
member NGC 7320B and NGC 7320C are members (as may be 7320A). The
annotated image identifies the galaxies that have redshifts and those
two without redshift data that might be members of the group as well as
the interloper, NGC 7320 itself. There's one quasar in the image hard
to pick out from NGC 7319 appearing more like a bright spot in the
galaxy. Also a star forming knot in the tidal plume coming from NGC
7319 is listed in NED as a separate galaxy though I think it is just a
star cloud in the plume, one of several in that plume.

So how did this group come to be so tidally damaged? There are many
theories. A note at NED summarizes them this way: "To explain the
peculiar morphology of Stephan's Quintet, a number of different
interaction scenarios have been suggested. Some of these scenarios
involve ram pressure stripping during a head-on collision between two
galaxies. For example, Peterson & Shostak (1980) suggest that a head-on
collision between NGC 7318B and NGC 7319 removed the gas and caused the
radio continuum ridge between them. A different scenario was suggested
by Shostak et al. (1984): a prograde tidal encounter of NGC 7320C and
NGC 7319 occurred, pulling gas out of these galaxies, creating the long
tail south of NGC 7319. This was followed by a high-speed collision
between NGC 7318A and NGC 7318B. Other scenarios involve a collision
between an "intruder galaxy" (usually NGC 7318B) and intragalactic gas
that had previously been tidally stripped or ram pressure-stripped in an
earlier encounter between two different galaxies in the group (van der
Hulst & Rots 1981; Moles et al. 1997). Moles et al. (1997) suggest that
a direct collision between the outlying galaxy NGC 7320C and NGC 7319
occurred in the recent past (10^8^ yr ago), removing a large quantity of
gas from these galaxies. After this event, NGC 7318B entered the group
at high velocity, colliding with this stripped gas and triggering star
formation." Pick one of your choosing or come up with another. Seems
to be still open for more ideas. Look up Arp 319 at NED and read the
notes for even more suggestions from users of the radio part of the
spectrum.

What I never saw mentioned is that NGC 7320 seems to have its own plume
extending to the southeast (left and some down). Is it from NGC 7320 or
is it really from NGC 7318B but mostly hidden by NGC 7320 until it
finally appears after passing behind it? I found nothing on this feature.

14" LX200R @ f/10, L=6x10' RGB=2x10'x3, STL-11000XM, Paramount ME

Rick
--
Prefix is correct. Domain is arvig dot net

Rick,

that's a very fine shot of this group.
Colour looks very good indeed.

Stefan

"Rick Johnson" schrieb im Newsbeitrag
.com...

I originally did this one in mono in 2006 and got some poor color data
in 2008. Not having proper software mating the two was a nightmare as
I'd made changes in my system and changed the image scale slightly.
Just recently I found I'd retaken the color data only weeks later after
the first try but under far better conditions. Now I have the software
needed to auto scale the two to match and better software for processing
the luminance channel. It still could use more luminance. Still this
is so much better than the 2008 try and uses color data that sat lost on
the hard drive for 5 years (well a different hard drive actually since
it was so old), It pretty well amounts to a new image. Much of the
first paragraph below is from back in 2006 and 2008 however.

Stephan's quintet is really a group of 4 galaxies with a 5th galaxy in
the foreground. Though it is much smaller so appears about the same
size as the others. The fake is NGC 7320. it is apparently the largest
of the group and the bluest. It is really a member of the so called
"Deer Lick" group located less than a degree away. It is located only
some 40 million light years away while the other 4 are about 270 million
light years from us. At one time this group was put forth by some to
disprove red shift as a distance measure to the universe. Since NGC
7320 is close it has a small redshift while the other 4 have a large
redshift. But if all were at the same distance then redshift was called
into question. It took Hubble to answer this for sure. It could
resolve stars in NGC 7320 but only massive star clusters in the others.
This was consistent with the redshift distances and it is now accepted
that 7320 is a Deer Lick member seen in front of the far more distant
group. Actually we do have 5 members of this distant group. To the
left a bit is a bared spiral whose arms make a nice ring, NGC 7320C.It
is now known to be a member of the group and may be responsible for some
of the tidal plumes. So there really are 5 galaxies in Stephan's
quintet, just that one isn't the one we thought was a member for many years.

For a shot taken with a far larger telescope on Kitt Peak than mine see:
http://www.noao.edu/image_gallery/html/im0414.html

Actually there are several more members of the group. Just that like
7320 is well away from its group these other members aren't as close by.
One is LEDA 141041 even further east than the first 5. Then there's
the very awkwardly named [WYV2002] 6 in the upper left corner of the
image. Just out of the image due east of the cluster is NGC 7320B yet
another member of the group. These are the only ones I found with
redshift values to show they are very likely group members. In the
lower part of the image is NGC 7320A which looks almost a twin of NGC
7320B I missed catching. Both these last two are members of the 2MASS
flat galaxy catalog. On the west side of the image is the S0 looking
galaxy PGC 69218. It too has no red shift data but could possibly be a
member of the group.

I find it interesting that while NGC 7320 is now known not to be a
member NGC 7320B and NGC 7320C are members (as may be 7320A). The
annotated image identifies the galaxies that have redshifts and those
two without redshift data that might be members of the group as well as
the interloper, NGC 7320 itself. There's one quasar in the image hard
to pick out from NGC 7319 appearing more like a bright spot in the
galaxy. Also a star forming knot in the tidal plume coming from NGC
7319 is listed in NED as a separate galaxy though I think it is just a
star cloud in the plume, one of several in that plume.

So how did this group come to be so tidally damaged? There are many
theories. A note at NED summarizes them this way: "To explain the
peculiar morphology of Stephan's Quintet, a number of different
interaction scenarios have been suggested. Some of these scenarios
involve ram pressure stripping during a head-on collision between two
galaxies. For example, Peterson & Shostak (1980) suggest that a head-on
collision between NGC 7318B and NGC 7319 removed the gas and caused the
radio continuum ridge between them. A different scenario was suggested
by Shostak et al. (1984): a prograde tidal encounter of NGC 7320C and
NGC 7319 occurred, pulling gas out of these galaxies, creating the long
tail south of NGC 7319. This was followed by a high-speed collision
between NGC 7318A and NGC 7318B. Other scenarios involve a collision
between an "intruder galaxy" (usually NGC 7318B) and intragalactic gas
that had previously been tidally stripped or ram pressure-stripped in an
earlier encounter between two different galaxies in the group (van der
Hulst & Rots 1981; Moles et al. 1997). Moles et al. (1997) suggest that
a direct collision between the outlying galaxy NGC 7320C and NGC 7319
occurred in the recent past (10^8^ yr ago), removing a large quantity of
gas from these galaxies. After this event, NGC 7318B entered the group
at high velocity, colliding with this stripped gas and triggering star
formation." Pick one of your choosing or come up with another. Seems
to be still open for more ideas. Look up Arp 319 at NED and read the
notes for even more suggestions from users of the radio part of the
spectrum.

What I never saw mentioned is that NGC 7320 seems to have its own plume
extending to the southeast (left and some down). Is it from NGC 7320 or
is it really from NGC 7318B but mostly hidden by NGC 7320 until it
finally appears after passing behind it? I found nothing on this feature.

14" LX200R @ f/10, L=6x10' RGB=2x10'x3, STL-11000XM, Paramount ME

Rick
--
Prefix is correct. Domain is arvig dot net