ASTRO: NGC 4163

NGC 4163 is a dwarf starburst galaxy that is part of the Ursa Major
group just west of the far better known and larger dwarf NGC 4214. It
is located in western Canes Venatici and about 935 million light-years
away. The HST has studied this and a couple other dwarf starburst
galaxies. You can read about it at
http://hubblesite.org/newscenter/arc.../2009/19/full/ Click
the "Release Images" tab to see the individual galaxy images. Hubble
had no trouble resolving it into stars. My seeing wasn't very good the
night I took this, over 3" so I resolved nothing I'm afraid. Maybe on a
better night. While redshift puts it at 20 million light-years this
method isn't reliable for such short distances. Study of the individual
stars, especially the tip of the red giant branch gives the more
reliable estimate of 9.3 to 9.5 million light-years. I show both (HST
determination in parentheses) in the annotated image.

West of NGC 4163 is the galaxy cluster WHL J121144.6+360943 with 23
members in the proverbial unknown area. The photographic redshift for
the cluster puts it at 3.5 billion light years but the spectroscopic
measurement of the BCG at its heart says 3.6 billion light-years which
is likely more accurate. Quite a few faint fuzzies are seen in the area
that are likely members but none anywhere near as big and bright as the
BCG of the same name as the cluster.

The galaxy cluster at the bottom of the image just right of center is
GMBCG J182.98714+36.02587 at a photographic redshift of 4.3 billion
light years. The same photographic redshift is reported for the BGC.

The NSCS J121108+360614 galaxy cluster to the southwest has no core
galaxy. It is listed as having 44 member but no radius is given. Many
faint fuzzies are in the area however. I assume many to be cluster
members. The annotated image denotes the center of the cluster as
defined in NED. The error circle is 15 arc seconds so the center is
rather ill defined compared to my line. Then all this got blown out of
the water when I noticed WHL J121105.2+360656, another galaxy cluster
less than a minute of arc away. It is said to have 11 members in that
same unknown radius at a photographic redshift of 3.4 billion
light-years. So which are which of which cluster is now something
unknown to me. This group does have a galaxy at the cluster's core
position (well in the center of its 15 arc second error radius. But it
isn't listed as a cD (cluster dominant or center dominant are corrupt
definitions but work here) or BGC (brightest galaxy in the cluster) nor
does it have a redshift that I found.

A more correct explanation of cD is that it is part of a galaxy
classification system from Yerkes Observatory in which c stands for a
very large galaxy while D is used for one that is very diffuse. Since
many central galaxies of a cluster are huge and diffuse SO or elliptical
galaxies due to having merged with many cluster members they get this
classification. But they are also the dominant galaxy in the cluster
and usually in the center hence the other uses of the term.

Just when you think things can't get more confusing up pops GMBCG
J182.77098+36.11180 BCG at 4.2 billion light-years determined
photographically. It is a BCG obviously but where was its cluster?
Then I noticed that NSCS J121108+360614 is listed at NED as also being
GMBCG J182.77098+36.11180! Note that the name contains the coordinates
of the position of the object. The position J182.77098+36.11180 matches
that of the BGC not the cluster's position. Is this an error? The
photographically determined distances don't match. About this time I
headed for the booze cabinet.

Near the edge of the upper right quadrant are a some galaxies at 1.7
billion light-years. Just off the edge of my image is the location of
the galaxy cluster MaxBCG J182.68333+36.25398 and its BCG. They are
shown at 1.7 billion light years. The cluster has no given radius and
14 members. Some appear to be labeled in my annotated image.

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

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

Rick,

you still got a lot of detail.
This is a strange little galaxy...

Stefan

"Rick Johnson" schrieb im Newsbeitrag
.com...
NGC 4163 is a dwarf starburst galaxy that is part of the Ursa Major
group just west of the far better known and larger dwarf NGC 4214. It
is located in western Canes Venatici and about 935 million light-years
away. The HST has studied this and a couple other dwarf starburst
galaxies. You can read about it at
http://hubblesite.org/newscenter/arc.../2009/19/full/ Click
the "Release Images" tab to see the individual galaxy images. Hubble
had no trouble resolving it into stars. My seeing wasn't very good the
night I took this, over 3" so I resolved nothing I'm afraid. Maybe on a
better night. While redshift puts it at 20 million light-years this
method isn't reliable for such short distances. Study of the individual
stars, especially the tip of the red giant branch gives the more
reliable estimate of 9.3 to 9.5 million light-years. I show both (HST
determination in parentheses) in the annotated image.

West of NGC 4163 is the galaxy cluster WHL J121144.6+360943 with 23
members in the proverbial unknown area. The photographic redshift for
the cluster puts it at 3.5 billion light years but the spectroscopic
measurement of the BCG at its heart says 3.6 billion light-years which
is likely more accurate. Quite a few faint fuzzies are seen in the area
that are likely members but none anywhere near as big and bright as the
BCG of the same name as the cluster.

The galaxy cluster at the bottom of the image just right of center is
GMBCG J182.98714+36.02587 at a photographic redshift of 4.3 billion
light years. The same photographic redshift is reported for the BGC.

The NSCS J121108+360614 galaxy cluster to the southwest has no core
galaxy. It is listed as having 44 member but no radius is given. Many
faint fuzzies are in the area however. I assume many to be cluster
members. The annotated image denotes the center of the cluster as
defined in NED. The error circle is 15 arc seconds so the center is
rather ill defined compared to my line. Then all this got blown out of
the water when I noticed WHL J121105.2+360656, another galaxy cluster
less than a minute of arc away. It is said to have 11 members in that
same unknown radius at a photographic redshift of 3.4 billion
light-years. So which are which of which cluster is now something
unknown to me. This group does have a galaxy at the cluster's core
position (well in the center of its 15 arc second error radius. But it
isn't listed as a cD (cluster dominant or center dominant are corrupt
definitions but work here) or BGC (brightest galaxy in the cluster) nor
does it have a redshift that I found.

A more correct explanation of cD is that it is part of a galaxy
classification system from Yerkes Observatory in which c stands for a
very large galaxy while D is used for one that is very diffuse. Since
many central galaxies of a cluster are huge and diffuse SO or elliptical
galaxies due to having merged with many cluster members they get this
classification. But they are also the dominant galaxy in the cluster
and usually in the center hence the other uses of the term.

Just when you think things can't get more confusing up pops GMBCG
J182.77098+36.11180 BCG at 4.2 billion light-years determined
photographically. It is a BCG obviously but where was its cluster?
Then I noticed that NSCS J121108+360614 is listed at NED as also being
GMBCG J182.77098+36.11180! Note that the name contains the coordinates
of the position of the object. The position J182.77098+36.11180 matches
that of the BGC not the cluster's position. Is this an error? The
photographically determined distances don't match. About this time I
headed for the booze cabinet.

Near the edge of the upper right quadrant are a some galaxies at 1.7
billion light-years. Just off the edge of my image is the location of
the galaxy cluster MaxBCG J182.68333+36.25398 and its BCG. They are
shown at 1.7 billion light years. The cluster has no given radius and
14 members. Some appear to be labeled in my annotated image.

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

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