ASTRO: Arp 227 revisited

This is another retry at an Arp entry I wasn't happy with the first time
around. I wanted to get a lot more time but the weather had other ideas
and most of the data wasn't usable due to horrid seeing and clouds.
There's a lot to talk about here. It's a long read for those
interested. The rest can just jump to the pictures.

Arp 227 falls into Arp's category for galaxies with concentric rings,
modern astronomers refer to it as a shell galaxy. It is located in
Pisces about 93 million light-years distant by redshift. Many papers
say 100 million which, given the uncertainty of redshift distances is a
nice round estimate I won't argue with. It consists of two galaxies,
NGC 474, the shell galaxy and a true companion NGC 470 to the west.
Another shell galaxy is in my image, NGC 467 to the southwest but it
would seem to be unrelated being some 2.5 times further away. While not
exceedingly rare, shell galaxies with such well defined shells as these
two are uncommon, to have two in the same small area of sky exceedingly
rare. I don't know of another example.

NGC 474 is classed as (R')SA(s)0^0^ at NED and (R')SA(s)0 at the NGC
project. Shell galaxies are thought to form a couple different ways.
One is a direct radial hit by a small, low mass, galaxy that is
destroyed in the process. Stars are flung out, turn around and fall
back. This, in simulations causes them to linger for a bit as they turn
around creating an area of higher density. Those with further orbits
before the companion was torn apart go out further to a more distant
turn around point. Thus high star density shells are formed. I don't
pretend to begin to understand this concept. The other method involves
a gazing impact that also destroys the companion. In this case its
stars are flung out into spiral-like loops that then loosely wrap about
the host galaxy like a fishing line snarl open face fishing reels can
create. At least I can understand the fishing line snarl but the rest
still eludes me. Arp, always the contrarian, has a really weird
explanation. The companion spirals in creating the rings. We do see
some such rings, in fact there's a few around our galaxy due to dwarf
galaxies our galaxy has and still is in one case, dining on. But they
are far from sharply defined as they are in shell galaxies. Arp though
goes on to say that both 474 and 470 are the remains of a larger active
galaxy and that the two quasars near 470, see my annotated version, were
ejected from the center of the original disrupted system. Of course he
uses his reworked physics to explain away their redshift that puts them
billions of light-years behind these two galaxies.

So how does NGC 470 fit into this? Wish I knew. None of the theories
seem to allow for it. It is classed as SA(rs)b by both NED and the NGC
project. It's arms are unusually thick and uneven. That could be
perfectly natural for it. Or could this be due to interaction with NGC
474. NGC 470 does have some small possible plumes coming off either end
that might indicate interaction with NGC 474 but doubt sufficient to
create the shells in the much larger galaxy yet be so little influenced
itself. Most papers on 474 say there's no other evidence of a collision
with another galaxy but for its shell structure. No second nucleus or
apparently evidence for two planes of stellar motion. Though if the
idea the companion was so low density to be totally destroyed the lack
of anything else but the shell structure isn't all that surprising to
me, but I'm far from an expert on this! I found papers saying the two
are and are not interacting. I vote with the latter but will reserve
the right to change my vote if better evidence for interaction is found.

A third member of the group is MGC +00-04-083 to the southwest. It has
about the same redshift but doesn't appear to be interacting with
anything and is quite small and insignificant compared to the other two.
A distant galaxy appears to overlap it to the NW of its core. This
little guy, as with most in the image is anonymous.

Then there's the other shell galaxy NGC 467 at nearly a quarter billion
light-years. It too has a companion, to the east southeast this time.
But this galaxy is not listed in NED. It too is apparently anonymous.
Is it a true companion or just a line of sight galaxy? Like NGC 474,
besides the well defined shells it too has plumes. The most obvious to
the south but if you look closely there's a faint arc of stars even
further north than the bright plume extends south. I needed more time
to bring these out in both galaxies. CGCG 385-068 at the very bottom of
my image to its southeast has a similar redshift and shows a faint tidal
tail. While I can't see it as causing the shells it could have had some
interaction creating the plumes I suppose.

This is one very busy image that could have used a lot more time. Maybe
a third try is needed.

There are 5 asteroids in the image, one seen atop the shells of NGC 474.
Details are on the annotated image.

Arp's image:
http://ned.ipac.caltech.edu/level5/A...ig_arp227.jpeg

14" LX200R @ f/10, L=8x10' RGB=2x10', STL-11000XM, Paramount ME

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

Rick,

mighty image showing the numerous shells.
I have a poor version at http://www.slilge.de/Binenwal/index_img/474-60gut.jpg.html
Only 60 minutes but under good skies, so I probably won’t get much deeper from the city.

Stefan

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

This is another retry at an Arp entry I wasn't happy with the first time
around. I wanted to get a lot more time but the weather had other ideas
and most of the data wasn't usable due to horrid seeing and clouds.
There's a lot to talk about here. It's a long read for those
interested. The rest can just jump to the pictures.

Arp 227 falls into Arp's category for galaxies with concentric rings,
modern astronomers refer to it as a shell galaxy. It is located in
Pisces about 93 million light-years distant by redshift. Many papers
say 100 million which, given the uncertainty of redshift distances is a
nice round estimate I won't argue with. It consists of two galaxies,
NGC 474, the shell galaxy and a true companion NGC 470 to the west.
Another shell galaxy is in my image, NGC 467 to the southwest but it
would seem to be unrelated being some 2.5 times further away. While not
exceedingly rare, shell galaxies with such well defined shells as these
two are uncommon, to have two in the same small area of sky exceedingly
rare. I don't know of another example.

NGC 474 is classed as (R')SA(s)0^0^ at NED and (R')SA(s)0 at the NGC
project. Shell galaxies are thought to form a couple different ways.
One is a direct radial hit by a small, low mass, galaxy that is
destroyed in the process. Stars are flung out, turn around and fall
back. This, in simulations causes them to linger for a bit as they turn
around creating an area of higher density. Those with further orbits
before the companion was torn apart go out further to a more distant
turn around point. Thus high star density shells are formed. I don't
pretend to begin to understand this concept. The other method involves
a gazing impact that also destroys the companion. In this case its
stars are flung out into spiral-like loops that then loosely wrap about
the host galaxy like a fishing line snarl open face fishing reels can
create. At least I can understand the fishing line snarl but the rest
still eludes me. Arp, always the contrarian, has a really weird
explanation. The companion spirals in creating the rings. We do see
some such rings, in fact there's a few around our galaxy due to dwarf
galaxies our galaxy has and still is in one case, dining on. But they
are far from sharply defined as they are in shell galaxies. Arp though
goes on to say that both 474 and 470 are the remains of a larger active
galaxy and that the two quasars near 470, see my annotated version, were
ejected from the center of the original disrupted system. Of course he
uses his reworked physics to explain away their redshift that puts them
billions of light-years behind these two galaxies.

So how does NGC 470 fit into this? Wish I knew. None of the theories
seem to allow for it. It is classed as SA(rs)b by both NED and the NGC
project. It's arms are unusually thick and uneven. That could be
perfectly natural for it. Or could this be due to interaction with NGC
474. NGC 470 does have some small possible plumes coming off either end
that might indicate interaction with NGC 474 but doubt sufficient to
create the shells in the much larger galaxy yet be so little influenced
itself. Most papers on 474 say there's no other evidence of a collision
with another galaxy but for its shell structure. No second nucleus or
apparently evidence for two planes of stellar motion. Though if the
idea the companion was so low density to be totally destroyed the lack
of anything else but the shell structure isn't all that surprising to
me, but I'm far from an expert on this! I found papers saying the two
are and are not interacting. I vote with the latter but will reserve
the right to change my vote if better evidence for interaction is found.

A third member of the group is MGC +00-04-083 to the southwest. It has
about the same redshift but doesn't appear to be interacting with
anything and is quite small and insignificant compared to the other two.
A distant galaxy appears to overlap it to the NW of its core. This
little guy, as with most in the image is anonymous.

Then there's the other shell galaxy NGC 467 at nearly a quarter billion
light-years. It too has a companion, to the east southeast this time.
But this galaxy is not listed in NED. It too is apparently anonymous.
Is it a true companion or just a line of sight galaxy? Like NGC 474,
besides the well defined shells it too has plumes. The most obvious to
the south but if you look closely there's a faint arc of stars even
further north than the bright plume extends south. I needed more time
to bring these out in both galaxies. CGCG 385-068 at the very bottom of
my image to its southeast has a similar redshift and shows a faint tidal
tail. While I can't see it as causing the shells it could have had some
interaction creating the plumes I suppose.

This is one very busy image that could have used a lot more time. Maybe
a third try is needed.

There are 5 asteroids in the image, one seen atop the shells of NGC 474.
Details are on the annotated image.

Arp's image:
http://ned.ipac.caltech.edu/level5/A...ig_arp227.jpeg

14" LX200R @ f/10, L=8x10' RGB=2x10', STL-11000XM, Paramount ME

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