ASTRO: Two more very strange galaxies from the UGC catalog

UGC 6912 and UGC 6931 are two interesting galaxies in Ursa Major about 3
degrees west of the double star M 40. Redshift puts them about 67-70
and 62 million light-years away. The difference is likely smaller than
this indicates. They may be related in fact. I put UGC 6912 high to
pick up both UGC 6931 and the rather "cute" galaxy cluster WHL
J115556.3+575501 west of UGC 6912 at 2 billion light-years. NGC 6912 is
classed by NED as S?. It certainly looks disturbed and would seem to
deserve a pec label. I found virtually nothing on this one that
attempts to explain how it ended up this way. Seems some sort of recent
interaction must be involved. Did it involve UGC 6912? Or is it a
merger in progress? Or something else?

UGC 6912 is described in the CGPG catalog as: "Distorted blue
post-eruptive spiral, exploded core, blue knots on spiral
arm." It certainly has several parts. The VV catalog lists three
parts, other catalogs add other pieces. Only one had redshift data.
NED considers this Sloan object to be a separate galaxy rather than just
a bright knot in the galaxy that the other parts are. If true it seems
way too blue to be the core of a merging galaxy. UGC 6912 is classed by
NED as SBm with strong HII emission. So it is possible but not a
requirement that it has been disturbed by something in the past. I
found even less on this galaxy in the literature. SIMBAD lists one
paper under both of these UGC galaxies that is labeled "The gas content
of peculiar galaxies: Strongly interacting systems." I found no
reference to either in the paper however so don't quite understand the
connection.

The galaxy cluster WHL J115556.3+575501 at the bottom of my image at 2
billion light-years is listed as having 24 members. Just below it, out
of the frame is the core of the galaxy cluster Abell 1415 which is also
shown at 2 billion light years. It is listed as 20 minutes in diameter
and of class 1 which 1 which contains 30 to 49 members. So it appears
WHL J115556.3+575501 constitutes a major part of the cluster. It is
classed as BM III which means it has no dominant galaxy. A big cluster
galaxy isn't necessarily a dominant galaxy. Thus while WHL
J115556.3+575501 has a BCG at its location the cluster doesn't seem to
cluster around it.

There are two main ways of classifying galaxy clusters. BM as used here
and RS. BM I has one dominant galaxy in the center. Abell 2199 is a
common example. BM II has a pair of dominant galaxies at its core.
Think Coma Cluster. BM III has no central galaxy or galaxies. The RS
series is more complex. If there is one core galaxy at its center it is
labeled cD and the galaxy is a cD galaxy. B means a binary system. So
these are similar to the first two BM classes. But the RS system goes
further. L means a line of bright galaxies, C a core of more than 4
bright galaxies, F a flattened distribution (that is the cluster has an
even distribution not that it is flat like a piece of paper) and I for
irregular with no obvious core region with a blotchy distribution rather
than a "flat" one. That would be similar to many BM III clusters
including this one. BM is Bautz-Morgan and RS Rood-Sastry. Didn't help
much did it? There are other systems such as Zwicky type which is
simply Compact, Medium-Compact and Open. They can be classified by
shape: Spherical, Intermediate and Irregular for instance. Many others
can be found in the literature.

I've included the Sloan survey image of UGC 6912. They had even more
trouble with that blasted field star than I did.

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

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

Two detailed and interesting galaxies. And galaxy cluster WHL
J115556.3+575501 is neat indeed.

Stefan

"Rick Johnson" schrieb im Newsbeitrag
.com...
UGC 6912 and UGC 6931 are two interesting galaxies in Ursa Major about 3
degrees west of the double star M 40. Redshift puts them about 67-70
and 62 million light-years away. The difference is likely smaller than
this indicates. They may be related in fact. I put UGC 6912 high to
pick up both UGC 6931 and the rather "cute" galaxy cluster WHL
J115556.3+575501 west of UGC 6912 at 2 billion light-years. NGC 6912 is
classed by NED as S?. It certainly looks disturbed and would seem to
deserve a pec label. I found virtually nothing on this one that
attempts to explain how it ended up this way. Seems some sort of recent
interaction must be involved. Did it involve UGC 6912? Or is it a
merger in progress? Or something else?

UGC 6912 is described in the CGPG catalog as: "Distorted blue
post-eruptive spiral, exploded core, blue knots on spiral
arm." It certainly has several parts. The VV catalog lists three
parts, other catalogs add other pieces. Only one had redshift data.
NED considers this Sloan object to be a separate galaxy rather than just
a bright knot in the galaxy that the other parts are. If true it seems
way too blue to be the core of a merging galaxy. UGC 6912 is classed by
NED as SBm with strong HII emission. So it is possible but not a
requirement that it has been disturbed by something in the past. I
found even less on this galaxy in the literature. SIMBAD lists one
paper under both of these UGC galaxies that is labeled "The gas content
of peculiar galaxies: Strongly interacting systems." I found no
reference to either in the paper however so don't quite understand the
connection.

The galaxy cluster WHL J115556.3+575501 at the bottom of my image at 2
billion light-years is listed as having 24 members. Just below it, out
of the frame is the core of the galaxy cluster Abell 1415 which is also
shown at 2 billion light years. It is listed as 20 minutes in diameter
and of class 1 which 1 which contains 30 to 49 members. So it appears
WHL J115556.3+575501 constitutes a major part of the cluster. It is
classed as BM III which means it has no dominant galaxy. A big cluster
galaxy isn't necessarily a dominant galaxy. Thus while WHL
J115556.3+575501 has a BCG at its location the cluster doesn't seem to
cluster around it.

There are two main ways of classifying galaxy clusters. BM as used here
and RS. BM I has one dominant galaxy in the center. Abell 2199 is a
common example. BM II has a pair of dominant galaxies at its core.
Think Coma Cluster. BM III has no central galaxy or galaxies. The RS
series is more complex. If there is one core galaxy at its center it is
labeled cD and the galaxy is a cD galaxy. B means a binary system. So
these are similar to the first two BM classes. But the RS system goes
further. L means a line of bright galaxies, C a core of more than 4
bright galaxies, F a flattened distribution (that is the cluster has an
even distribution not that it is flat like a piece of paper) and I for
irregular with no obvious core region with a blotchy distribution rather
than a "flat" one. That would be similar to many BM III clusters
including this one. BM is Bautz-Morgan and RS Rood-Sastry. Didn't help
much did it? There are other systems such as Zwicky type which is
simply Compact, Medium-Compact and Open. They can be classified by
shape: Spherical, Intermediate and Irregular for instance. Many others
can be found in the literature.

I've included the Sloan survey image of UGC 6912. They had even more
trouble with that blasted field star than I did.

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

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