ASTRO: Abell 2572 Hickson 94 Arp 170

Arp 170 is located in the Great Square of Pegasus at a distance of about
525 million light years. Arp classed it under galaxies with diffuse
counter-tails. It is part Hickson 94 which is part of the Abell 2572A a
subgroup of Abell 2572. Only the two brightest are part of Arp 170
however. The northern one is classed as E1 while the lower one with the
diffuse counter-tail is S0^0 pec. Both are also NGC 7578. One is 7578A
and the other 7578B. But which is which is an enigma. The NGC Project
and NED both claim the brighter is A. Both say the brighter is 0.6
magnitudes brighter. But they disagree as to which is the brighter! So
Prof. Cory with the NGC Project says the northern E1 galaxy is A while
NED and several other catalogs say it is the southern S0^0 galaxy. So
which is the brighter? At first glance it does appear the northern one
is but when you consider the large tidal plume of the southern one it
might be the brighter. It's certain the northern one is the easiest to
see visually from all reports I have read. Did the Herschels see both?
It's hard to say from their notes. To add to the confusion some
catalogs that use the UGC designations use UGC 12478 for the northern
one while others say it is UGC 12477 and of course they can't agree on
the southern one either. But since the UGC is supposed to be in RA
order that would make the northern 12478. Hickson assigned his galaxies
by magnitude and agrees the northern is the brightest by giving it the
H94A designation. But just when you think you have this figured out
another issue develops. The Kanipe-Webb book agrees with NED that the
northern galaxy is A but they assign it as Hickson 94B, while NED says
it is A. My head hurts. You'd think all this would be settled by now.
Arp had no comments on this entry nor did he enter into the
identification debate.

I'm not very certain of the color on this one. Fog rolled in during the
initial exposure. It really hit when I started to take the green and
then totally ruined the blue. So a couple nights later I retook the
green and blue. It wasn't until I went to process this I realized the
red was hurt by the fog as well. Since I have no measure of the loss of
red to the fog I first tried a normal G2V correction and got a disaster
showing the red was far worse than I thought. I then made a guess as to
the red fog correction based on the spectral type of the K2 star in the
image. But when I got it to the right color the galaxies were still
odd. I tried some manual tweaking that helped greatly but am not all
that sure of the color accuracy here.

While the SDSS hasn't covered this area this region is teaming with IR
galaxies in the 2MASS catalog, many of which have good red shift data.
While my color is likely not highly accurate I do believe the red color
of nearly every galaxy in this image is correct. An IR galaxy need not
appear red to our eye but they often do. That seems to be the case
here. Nor does a red galaxy necessarily mean it is a strong IR emitter.
Many in this particular field however are.

There are four other NGC galaxies in the image. All are members of the
Abell 2572 group and are east of Arp 170. One, labeled NGC 7571/7597,
has an identity crisis. Is it NGC 7578 (Arp 170) as the RNGC says or is
it NGC 7597 or is 7571 just non existent? On the annotated image I've
gone with NED and Prof. Cory saying it is both 7571 and 7597. You can
read all about it at the NGC project
http://www.ngcicproject.org/dss/dss_n7500.asp at the NGC 7571 entry.

I've prepared an annotated version. I've used NED's assignment of
Hickson letters to the group, as mentioned above this doesn't agree to
the Kanipe-Webb book as to A and B. Since it appears nearly all the
galaxies have about the same distance as Arp 170, being part of Abell
2572, I've just identified the larger ones. Those few that are nearer
or further than Arp 170 have their distance noted after the catalog
name. Some have no red shift data. I've added NRS for No Red Shift
data to the file name when this happened. All others are known to be
about the same distance as Arp 170 and thus likely members of the same
group. It's interesting they all have about the same color. Two
galaxies close together aren't in the catalogs but two very nearby are.
The brighter of the unlisted ones is barely within the error circle
for a radio source, NVSS J231822+184352. This nearly marks the center
of Abell 2572 the group to which most of the galaxies in this image belong.

I included on unusual galaxy, at least for its catalog designation, LT
32. This is the only designation for the galaxy in NED. It stands for
Laird Thompson who compiled a listing of "Possible ring galaxies near
rich clusters." There's 115 in the list. How this speck of a galaxy is
seen as a possible ring galaxy is beyond me. The coordinates match to
the pixel. Maybe longer exposures show a faint out ring I didn't pick
up. In fact what I imaged has the PSF of a star not a galaxy so maybe
the entire galaxy is too faint and I'll I picked up was field star atop it.


Arp's image taken under what looks like near perfect seeing atop Palomar
Mountain.
http://nedwww.ipac.caltech.edu/level...ig_arp170.jpeg
Ironic he'd waste such great seeing on such a low resolution object.
Maybe he hoped there was something of interest this seeing would make
visible.

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".

that is awfully large for something so far away.....

ditto on that one in my widefield M101 image


I talked to some others about that and it is simply nearly unbelievable that
the twin armed spiral in that image could have been over 1Bln light years
away....


"Rick Johnson" wrote in message
. com...
Arp 170 is located in the Great Square of Pegasus at a distance of about
525 million light years. Arp classed it under galaxies with diffuse
counter-tails. It is part Hickson 94 which is part of the Abell 2572A a
subgroup of Abell 2572. Only the two brightest are part of Arp 170
however. The northern one is classed as E1 while the lower one with the
diffuse counter-tail is S0^0 pec. Both are also NGC 7578. One is 7578A
and the other 7578B. But which is which is an enigma. The NGC Project
and NED both claim the brighter is A. Both say the brighter is 0.6
magnitudes brighter. But they disagree as to which is the brighter! So
Prof. Cory with the NGC Project says the northern E1 galaxy is A while
NED and several other catalogs say it is the southern S0^0 galaxy. So
which is the brighter? At first glance it does appear the northern one
is but when you consider the large tidal plume of the southern one it
might be the brighter. It's certain the northern one is the easiest to
see visually from all reports I have read. Did the Herschels see both?
It's hard to say from their notes. To add to the confusion some
catalogs that use the UGC designations use UGC 12478 for the northern
one while others say it is UGC 12477 and of course they can't agree on
the southern one either. But since the UGC is supposed to be in RA
order that would make the northern 12478. Hickson assigned his galaxies
by magnitude and agrees the northern is the brightest by giving it the
H94A designation. But just when you think you have this figured out
another issue develops. The Kanipe-Webb book agrees with NED that the
northern galaxy is A but they assign it as Hickson 94B, while NED says
it is A. My head hurts. You'd think all this would be settled by now.
Arp had no comments on this entry nor did he enter into the
identification debate.

I'm not very certain of the color on this one. Fog rolled in during the
initial exposure. It really hit when I started to take the green and
then totally ruined the blue. So a couple nights later I retook the
green and blue. It wasn't until I went to process this I realized the
red was hurt by the fog as well. Since I have no measure of the loss of
red to the fog I first tried a normal G2V correction and got a disaster
showing the red was far worse than I thought. I then made a guess as to
the red fog correction based on the spectral type of the K2 star in the
image. But when I got it to the right color the galaxies were still
odd. I tried some manual tweaking that helped greatly but am not all
that sure of the color accuracy here.

While the SDSS hasn't covered this area this region is teaming with IR
galaxies in the 2MASS catalog, many of which have good red shift data.
While my color is likely not highly accurate I do believe the red color
of nearly every galaxy in this image is correct. An IR galaxy need not
appear red to our eye but they often do. That seems to be the case
here. Nor does a red galaxy necessarily mean it is a strong IR emitter.
Many in this particular field however are.

There are four other NGC galaxies in the image. All are members of the
Abell 2572 group and are east of Arp 170. One, labeled NGC 7571/7597,
has an identity crisis. Is it NGC 7578 (Arp 170) as the RNGC says or is
it NGC 7597 or is 7571 just non existent? On the annotated image I've
gone with NED and Prof. Cory saying it is both 7571 and 7597. You can
read all about it at the NGC project
http://www.ngcicproject.org/dss/dss_n7500.asp at the NGC 7571 entry.

I've prepared an annotated version. I've used NED's assignment of
Hickson letters to the group, as mentioned above this doesn't agree to
the Kanipe-Webb book as to A and B. Since it appears nearly all the
galaxies have about the same distance as Arp 170, being part of Abell
2572, I've just identified the larger ones. Those few that are nearer
or further than Arp 170 have their distance noted after the catalog
name. Some have no red shift data. I've added NRS for No Red Shift
data to the file name when this happened. All others are known to be
about the same distance as Arp 170 and thus likely members of the same
group. It's interesting they all have about the same color. Two
galaxies close together aren't in the catalogs but two very nearby are.
The brighter of the unlisted ones is barely within the error circle
for a radio source, NVSS J231822+184352. This nearly marks the center
of Abell 2572 the group to which most of the galaxies in this image
belong.

I included on unusual galaxy, at least for its catalog designation, LT
32. This is the only designation for the galaxy in NED. It stands for
Laird Thompson who compiled a listing of "Possible ring galaxies near
rich clusters." There's 115 in the list. How this speck of a galaxy is
seen as a possible ring galaxy is beyond me. The coordinates match to
the pixel. Maybe longer exposures show a faint out ring I didn't pick
up. In fact what I imaged has the PSF of a star not a galaxy so maybe
the entire galaxy is too faint and I'll I picked up was field star atop
it.


Arp's image taken under what looks like near perfect seeing atop Palomar
Mountain.
http://nedwww.ipac.caltech.edu/level...ig_arp170.jpeg
Ironic he'd waste such great seeing on such a low resolution object.
Maybe he hoped there was something of interest this seeing would make
visible.

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".