The galaxies NGC 4725, NGC 4747, NGC 4712 form the optical galaxy triplet Holm 468. While NGC 4725 and NGC 4747 are real neighbors and interacting, NGC 4712 is much further away and is simply optically aligned with the other two.
NGC 4725NGC 4725, the main charachter of this picture, is an intermediate barred spiral galaxy with a prominent ring structure, located in the northern constellation of Coma Berenices near the north galactic pole. It was discovered by William Herschel on April 6, 1785. The galaxy lies at a distance of approximately 40 Mly from us and its estimated diameter is 150000 kly, bigger than our Milky Way.
NGC 4725 is the brightest member of the Coma I Group of the Coma-Sculptor Cloud (see below), although it is relatively isolated from the other members of this group. This galaxy is strongly disturbed and is interacting with neighboring spiral galaxy NGC 4747, with its spiral arms showing indications of warping. The pair have an angular separation of 24′, which corresponds to a projected linear separation of 370 kly. A tidal plume extends from NGC 4747 toward NGC 4725.
This is a suspected type 2 Seyfert galaxy with a supermassive black hole at the core. It shows a complete ring surrounding the bar, that is a region of star formation. There is a compact radio source positioned approximately 6.2 kly from the nucleus with no optical counterpart at that position, therefore this may be a star forming region that is heavily obscured by dust.
The Coma I and Coma II Group (see picture below)The Coma I Group is a group of galaxies located about 14.5 Mpc (47.3 Mly) away in the constellation Coma Berenices. The brightest member of the group is our NGC 4725. The Coma I Group is rich in spiral galaxies while containing few elliptical and lenticular galaxies. Coma I lies in the foreground of the more distant Coma and Leo clusters and is located within the Virgo Supercluster. The Coma I Group is currently infalling into the Virgo Cluster, as our Local Group is doing, and will eventually merge with it.
Gibson et al. suggests a different association, the Coma II Group, which is centered on NGC 4725, to be in relationship with the Coma I Group. In 2000, Ferrarese et al. defined the Coma II Group as containing 5 galaxies, namely NGC 4494, NGC 4562, NGC 4565, NGC 4725, and NGC 4747. Also, it was found that these 5 galaxies which make up the Coma II Group have radial velocities in the narrow range of 1190 to 1395 km/s which is larger than the range of galaxies that are part of the Coma I group which have ranges of 600 to 1000 km/s.
NGC 4747, Arp 159NGC 4747 is located at a distance of about 35 million light years from Earth, which, given its apparent dimensions, means that NGC 4747 is about 35,000 light years across. It was discovered by William Herschel on April 6, 1785. It is included in the Atlas of Peculiar Galaxies in the interior absorption category.
NGC 4747 is interacting with neighboring spiral galaxy NGC 4725, with its spiral arms showing indications of warping. As already said before, the pair have a linear separation of 370 kly. A close approach between NGC 4747 and the more massive NGC 4725 that took place 320 million years before observed created tidal plumes in NGC 4747.
A short tidal plume extends from NGC 4747 toward NGC 4725, to the south-west, and one more pronounced towards the north-east, with a length of 8 arc-minutes. Two knots, possibly star clusters, have been identified in the northeast plume, that could become tidal dwarf galaxies, as they appear to be massive enough to be self-gravitating.
NGC 4712NGC 4712 is a spiral galaxy with extensive Hubble-type Sbc star-forming regions. It is an estimated 196 million light-years from the Milky Way and about 155,000 light-years across. The galaxy is receding from the solar system at a calculated radial velocity of approximately 4,400 kilometers per second.
It was discovered by John Herschel on March 28, 1832.
Picture: The Coma I Group members are marked in yellow. The red perimeter indicates approximately the field portrayed here. Just above left the red frame is visible the Coma Abell 1656 galaxy cluster, much further away than the Coma I Group. My elaboration of a Cartes du Ciel screenshot.
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