Norma Galaxy Clusters

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Center of the Norma Galaxy Cluster. The giant galaxies ESO 137-8 (left) and ESO 137-6 (right) can be seen in the middle .

The Norma galaxy cluster (also Abell 3627 ) is a large galaxy cluster in the southern sky at the border of the constellation Winkel Maß (Norma) to the constellation Southern Triangle . At about 65 Mpc (210 million light years ) away , it is significantly closer to us than the Coma Cluster, and therefore the closest known rich galaxy cluster. Its mean radial speed is 4870 km / s and corresponds to a redshift of z = 0.016.

Although it is close and bright at the same time, it is difficult to observe because it is towards the edge of our Milky Way system , so it is partially obscured by interstellar dust and observation is made difficult by the high density of foreground stars. It therefore eluded the research community for a long time. That changed when a group of researchers led by Donald Lynden-Bell , who became known as "the seven samurai", postulated the existence of a large attractor that influences the movement of all galaxies in the cosmic neighborhood and is located behind the so-called "avoidance zone" ( Engl. zone of avoidance ) in the direction of the constellation angle measure. Since 1996, the Norma Galaxy Cluster has been an integral part of the Great Attractor and is being studied in depth.

Structure of the heap

The Norma galaxy cluster contains about 300 more closely examined galaxies, which are distributed over its Abell radius of about 2 Mpc (corresponding to 1.75 ° in the sky). The total number of larger galaxies, however, will be significantly higher, of which around 600 are now known. The mass of the Norma galaxy cluster was independently determined by analysis of its X-rays (from ROSAT and ASCS measurements) and by means of dynamic models ( virial theorem ) from the peculiar velocity of its members to a magnitude of 10 15 solar masses and thus appears to be somewhat less massive than to be the coma bunch.

In the center of the cluster are the two CD galaxies ESO137-6 (PGC 57612) and ESO 137-8 (PGC 57649). The presence of these two giant elliptical galaxies is a property that the galaxy cluster shares with other clusters (including the Coma cluster) and is called type B (for binary ) in the Rood and Sastry scheme . Abell classified the cluster as Type I (irregular) in the Bautz and Morgan scheme. The entire cluster has an elongated structure that points in the direction of a chain of galaxy clusters stretching from the Pavo II galaxy cluster through the Centaurus Crux galaxy cluster .

Of the approximately 300 more closely examined galaxies in the cluster, a total of 36% are elliptical or lenticular ( Hubble types E and S0) and 64% are spiral or irregular (types S and Irr). The S / Irr population is clearly divided into two subgroups, one of which ( Norma A ) is located near the center of the cluster, the other ( Norma B ) about 1 ° northwest of the center and thus in the direction of the elongated filament structure that seems to connect the Norma cluster to its neighboring cluster.

The two central giant galaxies dominate the cluster center, which geometrically and dynamically coincides quite exactly with ESO137-6. This galaxy is one of the 20 strongest extragalactic radio sources and is listed as such under the name PKS B1610-608. It is also the center of stronger X-rays. Also striking is the high peculiar speed of a good 500 km / s, which could indicate an imminent merger within a subheap. In the optical range, both giant galaxies have an apparent brightness of a good 13  mag .

The Chandra - and the XMM-Newton - X-ray telescopes discovered a 200,000 light-year long gas tail in the barred spiral galaxy ESO 137-1 (PGC 57532), which is moving towards the center of Abell 3627 , in which a large number of new stars are forming. This is currently (as of September 2007) the longest gas tail discovered in galaxies to date. In January 2010, a second gas tail was discovered, which also emanates from the galaxy ESO 137-1.

Data

  • Right ascension : 16 h 15 m
  • Declination : −60 ° 56 '
  • Galactic longitude: 325 °
  • Galactic latitude: −7 °
  • Distance: 210 million light years (65 Mpc , redshift z = 0.016)
  • Brightness of the brightest galaxy: 12.8 mag
  • Diameter: about 3.5 °

Data sources

Footnotes

  1. ↑ a b c A Hubble constant of H = 73 km / s / Mpc is assumed for these data .

Individual evidence

  1. ↑ Kraan-Korteweg, RC, Woudt, PA, Cayatte, V., Fairall, AP, Balkowski, Henning, P. A: A nearby massive galaxy cluster behind the Milky Way . In: Nature . tape 379 , Feb. 1996, 1996, pp. 519-521 , doi : 10.1038 / 379519a0 .
  2. ↑ a b c d e P.A. Woudt, RC Kraan-Korteweg, J. Lucey, AP Fairall, SAW Moore: The Norma Cluster (ACO 3627): I. A Dynamical Analysis of the Most Massive Cluster in the Great Attractor . In: Monthly Notices of the Royal Astronomical Society . tape 383 , no. 2 , 2008, p. 445-457 , doi : 10.1111 / j.1365-2966.2007.12571.x .
  3. ↑ Chandra Photo Album with explanation (English)
  4. ↑ Astronews.com: A galaxy with two gas tails.
  5. ↑ Astronomy Picture of the Day: Stripping ESO 137-001
  6. ↑ NASA / IPAC Extragalactic Database . In: Results for NormaCluster . Retrieved October 14, 2007.