WBL 706 Galaxy Group and a famous telescope

The WBL 706 galaxy group has three members. They are NGC7594, IC 5305 and the double galaxy of LEDA 1376799 and IC 5306 though IC 5306 is only a line of sight galaxy. The three true members are all about a half billion light-years distant. NGC 7594 is a Sb galaxy with a redshift distance of 470 million light-years but non redshift measurements have a median value of 420 million light-years and a mean value of 530 million light-years. IC 5305 shows a redshift of 460 million light-years while LEDA 1376799 has the largest redshift of 530 million light-years. The outcast IC 5306 is only 330 million light-years distant by redshift. Though other galaxies are apparently true members of the group such as IC 5307 at 54 million light-years and PGC 070958 at 53 million light-years they aren't part of the WBL group for some reason (too far away from the other three by angular measurement? The group is located in Pegasus below the Great Square.

Since these are quite distant galaxies but have a reasonable angular size they must be huge. NGC 7594 is about 200,000 light-years across making it one of the largest known spiral galaxies. LEDA 1376799 is 131,000 light-years in diameter while IC 5305 is only 80,000 light-years in size. I should probably mention that measuring the size of such distant galaxies has an additional complication not found with nearer galaxies. During the half billion years the light has been heading our way the universe has expanded. So while we see these galaxies at one distance they were closer when the light left. We see their size as it would be if they were at the distance they were when the light left but measure their distance in light travel time as greater. That means we get a size that is too large. In fact we call its distance when the light left its angular size distance. At some point this difference is material. I usually round distances to only two significant digits so it hardly matters in most cases. But since I get asked about it decided its time to address this issue. In the case of NGC 7594 its angular size distance is about 2 megaparsecs closer. If I use the redshift look back distance to calculate its size and use all 3 significant digits at NED (0.473) and its measured size on my FIT of 90 arc seconds that makes it 206,000 light-years across. Using its Angular Size Distance of 143 megaparsecs (0.466) its size is 203,000 light-years. Being conservative I used 200,000 above as I round to 2 significant digits since the calculation was done using 3. I always use one less significant digit in these posts. Since the two values are on opposite sides of the rounding point if I'd have used the look back distance for the calculation it would have been 210,000 which is too big by 5%. Since there are so many error bars involved here even using 200,000 might be a bit over stating the actual accuracy of the computation. I could throw out that during the half billion years the light was on the way the galaxy actually moved further away than the light travel time indicates and it is now really 148 megaparsecs distant (482 million light-years). I'm assuming values NED uses for their 5 year WMAP calculations. Change these values and the distances change accordingly. New values come out every few months. I've stuck with these over the years to make all my posts comparable. If I kept changing each time a new value came out I'd have to change all prior posts to match and with over 1000 of them now that is impossible. Again the various error bars involved and my rounding likely make these difference rather immaterial.

NGC 7594 was discovered twice. First by Andrew Commen in August 1880 and again by Guillaume Bigourdan in August 22, 1889. The latter was entered into the IC catalog as IC 1478. This is why I listed both on the annotated image. Andrew Commen was an English astronomer who used a 36" f/5.9 reflector. He later sold this in 1885 to a rich carpet baron on England by the name of Edward Crossley who set up his own observatory using the scope. But English weather got the best of him and gave up the astronomy side of his life. He donated scope and dome to Lick Observatory where it was known as the Crossley reflector for its donor. It was only recently retired from research service. http://www.ucolick.org/public/telescopes/crossley.html

IC 5305, 5306 and 5307 were discovered in 1897 by Hermann Kobold using an 18" refractor at Strasbourg Observatory. He found 38 IC objects but 4 turned out to be stars. The majority of his discoveries were galaxies in the Coma Cluster.

This field is poorly mapped. Only a few galaxies had redshift values. Most have no redshift. Those listed by NED are mostly from the 2MASS catalog and often don't even have a magnitude. Most of the background galaxies however don't emit enough 2 micron radiation to make that survey. Those that are strong in Ultraviolet made the Galex satellites catalog of Ultraviolet Sources (UvS) but so far NED lists those solely as UvS. Most are stars, some galaxies but NED makes no distinction. Also the resolution and pointing accuracy of the satellite was low by today's standards so the positions are somewhat vague. Since the annotated image was rather sparse due to lack of redshift data I included the brighter 2MASS objects by designation (just their coordinates in the sky). I didn't even do that with the UvS galaxies I noted. Just listing them as UvS. Many more UvS and 2MASS galaxies are in the image. I didn't see much use in pointing the few remaining 2MASS galaxies out and separating galaxies from stars in the Galex catalog is a super time consuming task with hundreds to go through. Probably why NED hasn't done so as yet.

There are three asteroids in the image. See the annotated image for details.

I should note I have no idea why I took this group. It isn't to be found on my to-do list in any category. That means I had to interrupt the auto selection process and go to it manually. Something I rarely do unless a super nova, comet, near earth asteroid or other in the news object comes up. That doesn't seem to be the case here. I did enter it in the log under the NGC 7594 designation not the galaxy group designation which is also odd. I made no note however as to why it was taken. Apparently I figured I'd remember why when I processed it but I don't. Apparently the why will remain a mystery.

14" LX200R @ f/10, L=4x10' RGB=2x10, STL-11000XM, Paramount ME

Rick

Rick,

that's a neat group, all those different galaxies in one place.

Stefan


"WA0CKY" schrieb im Newsbeitrag ...


The WBL 706 galaxy group has three members. They are NGC7594, IC 5305
and the double galaxy of LEDA 1376799 and IC 5306 though IC 5306 is only
a line of sight galaxy. The three true members are all about a half
billion light-years distant. NGC 7594 is a Sb galaxy with a redshift
distance of 470 million light-years but non redshift measurements have a
median value of 420 million light-years and a mean value of 530 million
light-years. IC 5305 shows a redshift of 460 million light-years while
LEDA 1376799 has the largest redshift of 530 million light-years. The
outcast IC 5306 is only 330 million light-years distant by redshift.
Though other galaxies are apparently true members of the group such as
IC 5307 at 54 million light-years and PGC 070958 at 53 million
light-years they aren't part of the WBL group for some reason (too far
away from the other three by angular measurement? The group is located
in Pegasus below the Great Square.

Since these are quite distant galaxies but have a reasonable angular
size they must be huge. NGC 7594 is about 200,000 light-years across
making it one of the largest known spiral galaxies. LEDA 1376799 is
131,000 light-years in diameter while IC 5305 is only 80,000 light-years
in size. I should probably mention that measuring the size of such
distant galaxies has an additional complication not found with nearer
galaxies. During the half billion years the light has been heading our
way the universe has expanded. So while we see these galaxies at one
distance they were closer when the light left. We see their size as it
would be if they were at the distance they were when the light left but
measure their distance in light travel time as greater. That means we
get a size that is too large. In fact we call its distance when the
light left its angular size distance. At some point this difference is
material. I usually round distances to only two significant digits so
it hardly matters in most cases. But since I get asked about it decided
its time to address this issue. In the case of NGC 7594 its angular
size distance is about 2 megaparsecs closer. If I use the redshift look
back distance to calculate its size and use all 3 significant digits at
NED (0.473) and its measured size on my FIT of 90 arc seconds that makes
it 206,000 light-years across. Using its Angular Size Distance of 143
megaparsecs (0.466) its size is 203,000 light-years. Being conservative
I used 200,000 above as I round to 2 significant digits since the
calculation was done using 3. I always use one less significant digit
in these posts. Since the two values are on opposite sides of the
rounding point if I'd have used the look back distance for the
calculation it would have been 210,000 which is too big by 5%. Since
there are so many error bars involved here even using 200,000 might be a
bit over stating the actual accuracy of the computation. I could throw
out that during the half billion years the light was on the way the
galaxy actually moved further away than the light travel time indicates
and it is now really 148 megaparsecs distant (482 million light-years).
I'm assuming values NED uses for their 5 year WMAP calculations. Change
these values and the distances change accordingly. New values come out
every few months. I've stuck with these over the years to make all my
posts comparable. If I kept changing each time a new value came out I'd
have to change all prior posts to match and with over 1000 of them now
that is impossible. Again the various error bars involved and my
rounding likely make these difference rather immaterial.

NGC 7594 was discovered twice. First by Andrew Commen in August 1880
and again by Guillaume Bigourdan in August 22, 1889. The latter was
entered into the IC catalog as IC 1478. This is why I listed both on
the annotated image. Andrew Commen was an English astronomer who used a
36" f/5.9 reflector. He later sold this in 1885 to a rich carpet baron
on England by the name of Edward Crossley who set up his own observatory
using the scope. But English weather got the best of him and gave up
the astronomy side of his life. He donated scope and dome to Lick
Observatory where it was known as the Crossley reflector for its donor.
It was only recently retired from research service.
http://www.ucolick.org/public/telescopes/crossley.html

IC 5305, 5306 and 5307 were discovered in 1897 by Hermann Kobold using
an 18" refractor at Strasbourg Observatory. He found 38 IC objects but
4 turned out to be stars. The majority of his discoveries were galaxies
in the Coma Cluster.

This field is poorly mapped. Only a few galaxies had redshift values.
Most have no redshift. Those listed by NED are mostly from the 2MASS
catalog and often don't even have a magnitude. Most of the background
galaxies however don't emit enough 2 micron radiation to make that
survey. Those that are strong in Ultraviolet made the Galex satellites
catalog of Ultraviolet Sources (UvS) but so far NED lists those solely
as UvS. Most are stars, some galaxies but NED makes no distinction.
Also the resolution and pointing accuracy of the satellite was low by
today's standards so the positions are somewhat vague. Since the
annotated image was rather sparse due to lack of redshift data I
included the brighter 2MASS objects by designation (just their
coordinates in the sky). I didn't even do that with the UvS galaxies I
noted. Just listing them as UvS. Many more UvS and 2MASS galaxies are
in the image. I didn't see much use in pointing the few remaining 2MASS
galaxies out and separating galaxies from stars in the Galex catalog is
a super time consuming task with hundreds to go through. Probably why
NED hasn't done so as yet.

There are three asteroids in the image. See the annotated image for
details.

I should note I have no idea why I took this group. It isn't to be
found on my to-do list in any category. That means I had to interrupt
the auto selection process and go to it manually. Something I rarely do
unless a super nova, comet, near earth asteroid or other in the news
object comes up. That doesn't seem to be the case here. I did enter it
in the log under the NGC 7594 designation not the galaxy group
designation which is also odd. I made no note however as to why it was
taken. Apparently I figured I'd remember why when I processed it but I
don't. Apparently the why will remain a mystery.

14" LX200R @ f/10, L=4x10' RGB=2x10, STL-11000XM, Paramount ME

Rick


--
WA0CKY