ASTRO: ARP 135

Arp 135, NGC 1023, is also the namesake of a galaxy group -- the NGC
1023 group of course. It is much closer however at only about 20
million light years. So it is right in our back yard! It contains 8
members, 4 of which are in my image.

Arp classed this one under "Elliptical or Elliptical Like Galaxies with
Nearby Fragments". Arp 135 would be "elliptical like" as it is actually
a SB0 galaxy. SB for barred spiral (we are looking right down the bar
so it isn't very obvious) and the 0 means there is little to no dust and
gas remaining in the galaxy -- the same as an elliptical galaxy.
Without dust and gas there can be little to no star formation so the
stars are all old ones. Since blue stars are short lived there can be
few if any in a galaxy without star formation going on. This is why the
galaxy is a yellowish orange color, the color of stars that have a long
enough life span to still be around after star formation ceased. The
"fragment" Arp refers to is NGC 1023A, the blue object at the left end
of the galaxy. It is classed as a blue irregular galaxy with a question
mark indicating this is not a firm classification. It has a somewhat
different redshift than the part of Arp 135 "behind" it so likely really
is a separate galaxy. I say behind as that's what it looks like. It
may well be in front of it. In any case it is moving away from us about
25% faster than Arp 135 so if it is in front a collision may be in the
future.

It is one of the 8 galaxies in the cluster in any case. The blue color
would indicate it isn't related to Arp 135 though interaction with Arp
135 is likely triggering the star formation. Arp 135 appears to have
lost its dust and gas at least a couple billion years ago so would have
none to contribute to this object making it unlikely it is just part of
Arp 135, its differing red shift would also indicate this. The other
members of the group in my image are also quite blue. They are NGC 1023
B (classed simply as a dwarf galaxy) further left of 1023 and almost
hidden under a very bright star. The 4th member is the dwarf spiral
looking galaxy NGC 1023D (also classed as a dwarf with no mention of it
being a spiral) near the bottom edge of the image directly below Arp
135. Even its core appears blue, probably why it is not considered a
spiral. Why these galaxies have so much star formation still possible
while Arp 135 doesn't is not explained in any of the literature I
consulted. In case you are wondering NGC 1023C is far out of the frame
above Arp 135, it too is classed as a dwarf. I didn't look up the other
members since they all were out of frame. All 8 fit in an area of space
of 6 million cubic light years.

Arp's Palomar telescope view of it is at:
http://nedwww.ipac.caltech.edu/level...ig_arp135.jpeg

14" LX200R @ f/10, L=4x10 RGB=2x10, STL-11000XM, Paramount ME
Usually I bin color 3x3 but in this case it was binned 2x2, same as the
lum image.

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".

Good shooting Rick. I wasn't aware that NGC 1023A has a different colour
than the "main" object.

Stefan

"Rick Johnson" schrieb im Newsbeitrag
ster.com...
Arp 135, NGC 1023, is also the namesake of a galaxy group -- the NGC
1023 group of course. It is much closer however at only about 20
million light years. So it is right in our back yard! It contains 8
members, 4 of which are in my image.

Arp classed this one under "Elliptical or Elliptical Like Galaxies with
Nearby Fragments". Arp 135 would be "elliptical like" as it is actually
a SB0 galaxy. SB for barred spiral (we are looking right down the bar
so it isn't very obvious) and the 0 means there is little to no dust and
gas remaining in the galaxy -- the same as an elliptical galaxy.
Without dust and gas there can be little to no star formation so the
stars are all old ones. Since blue stars are short lived there can be
few if any in a galaxy without star formation going on. This is why the
galaxy is a yellowish orange color, the color of stars that have a long
enough life span to still be around after star formation ceased. The
"fragment" Arp refers to is NGC 1023A, the blue object at the left end
of the galaxy. It is classed as a blue irregular galaxy with a question
mark indicating this is not a firm classification. It has a somewhat
different redshift than the part of Arp 135 "behind" it so likely really
is a separate galaxy. I say behind as that's what it looks like. It
may well be in front of it. In any case it is moving away from us about
25% faster than Arp 135 so if it is in front a collision may be in the
future.

It is one of the 8 galaxies in the cluster in any case. The blue color
would indicate it isn't related to Arp 135 though interaction with Arp
135 is likely triggering the star formation. Arp 135 appears to have
lost its dust and gas at least a couple billion years ago so would have
none to contribute to this object making it unlikely it is just part of
Arp 135, its differing red shift would also indicate this. The other
members of the group in my image are also quite blue. They are NGC 1023
B (classed simply as a dwarf galaxy) further left of 1023 and almost
hidden under a very bright star. The 4th member is the dwarf spiral
looking galaxy NGC 1023D (also classed as a dwarf with no mention of it
being a spiral) near the bottom edge of the image directly below Arp
135. Even its core appears blue, probably why it is not considered a
spiral. Why these galaxies have so much star formation still possible
while Arp 135 doesn't is not explained in any of the literature I
consulted. In case you are wondering NGC 1023C is far out of the frame
above Arp 135, it too is classed as a dwarf. I didn't look up the other
members since they all were out of frame. All 8 fit in an area of space
of 6 million cubic light years.

Arp's Palomar telescope view of it is at:
http://nedwww.ipac.caltech.edu/level...ig_arp135.jpeg

14" LX200R @ f/10, L=4x10 RGB=2x10, STL-11000XM, Paramount ME
Usually I bin color 3x3 but in this case it was binned 2x2, same as the
lum image.

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".

I didn't realize it either until I started to put this image together.

Rick

Stefan Lilge wrote:

Good shooting Rick. I wasn't aware that NGC 1023A has a different colour
than the "main" object.

Stefan

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

Arp 135, NGC 1023, is also the namesake of a galaxy group -- the NGC
1023 group of course. It is much closer however at only about 20
million light years. So it is right in our back yard! It contains 8
members, 4 of which are in my image.

Arp classed this one under "Elliptical or Elliptical Like Galaxies with
Nearby Fragments". Arp 135 would be "elliptical like" as it is actually
a SB0 galaxy. SB for barred spiral (we are looking right down the bar
so it isn't very obvious) and the 0 means there is little to no dust and
gas remaining in the galaxy -- the same as an elliptical galaxy.
Without dust and gas there can be little to no star formation so the
stars are all old ones. Since blue stars are short lived there can be
few if any in a galaxy without star formation going on. This is why the
galaxy is a yellowish orange color, the color of stars that have a long
enough life span to still be around after star formation ceased. The
"fragment" Arp refers to is NGC 1023A, the blue object at the left end
of the galaxy. It is classed as a blue irregular galaxy with a question
mark indicating this is not a firm classification. It has a somewhat
different redshift than the part of Arp 135 "behind" it so likely really
is a separate galaxy. I say behind as that's what it looks like. It
may well be in front of it. In any case it is moving away from us about
25% faster than Arp 135 so if it is in front a collision may be in the
future.

It is one of the 8 galaxies in the cluster in any case. The blue color
would indicate it isn't related to Arp 135 though interaction with Arp
135 is likely triggering the star formation. Arp 135 appears to have
lost its dust and gas at least a couple billion years ago so would have
none to contribute to this object making it unlikely it is just part of
Arp 135, its differing red shift would also indicate this. The other
members of the group in my image are also quite blue. They are NGC 1023
B (classed simply as a dwarf galaxy) further left of 1023 and almost
hidden under a very bright star. The 4th member is the dwarf spiral
looking galaxy NGC 1023D (also classed as a dwarf with no mention of it
being a spiral) near the bottom edge of the image directly below Arp
135. Even its core appears blue, probably why it is not considered a
spiral. Why these galaxies have so much star formation still possible
while Arp 135 doesn't is not explained in any of the literature I
consulted. In case you are wondering NGC 1023C is far out of the frame
above Arp 135, it too is classed as a dwarf. I didn't look up the other
members since they all were out of frame. All 8 fit in an area of space
of 6 million cubic light years.

Arp's Palomar telescope view of it is at:
http://nedwww.ipac.caltech.edu/level...ig_arp135.jpeg

14" LX200R @ f/10, L=4x10 RGB=2x10, STL-11000XM, Paramount ME
Usually I bin color 3x3 but in this case it was binned 2x2, same as the
lum image.

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".