Zlender Images

Groups and Clusters of Galaxies

 It is quite unusual for galaxies to exist as singles, to float through space and time in an otherwise empty region of the universe. Most of them form groups of dozens to thousands. Our own Galaxy belongs together with the Andromeda galaxy and more than thirty smaller ones to the so called Local Group of galaxies which is thought to be part of the outer regions of  the Virgo cluster, the next large cluster,  located some 50 million light-years from us. The members of these conglomerations are in mutual gravitational interaction which causes dramatic changes in the appearance of many of them. In fact, almost all members of dense clusters have gone through close encounters and have lost their interstellar matter in those events. Modern X-ray observatories, orbiting earth since several years, like the german ROSAT, have found that this matter fills large regions of space around the centers of rich clusters and contributes in a much larger fraction to the total mass of the cluster than the visible matter in galaxies does. An analysis showed that the amount of mass is related to the temperature of the gas, which ranges from 10 million degrees in smaller groups to more than hundred millions in the largest clusters. The X-rays are emitted in a process called bremsstrahlung. Here a lonely electron has an exciting close encounter with an attractive atomic nucleus, somewhere in intracluster space where it looses much energy while it changes course abruptly. Another result of the cosmic strip tease described above, is that most of these galaxies are ellipticals or lenticulars (S0), consisting of old stellar populations only. Star formation is found in spiral and irregular galaxies, where a large fraction of the matter is found as gas and dust, serving as building material for new stars. There are examples where cluster formation is still in progress, as it is in the case of the Virgo cluster. Only few ellipticals and many spirals can be found here. Others, like the  Coma Cluster  are rich in ellipticals and S0-galaxies and miss the spirals. It seems that they have reached this evolutionary state billions of years ago. The form of these old  clusters is regular and spherical, in opposition to an unsymmetric appearance of the Virgo cluster. The centers of the clusters are dominated by a giant elliptical galaxy like  M87  in Virgo, often by two monsters as in the case of the Coma cluster (NGC 4874 and NGC 4889) or several as can be seen in CL 0024+1645 a very distant cluster in Pisces, famous because in also serves as the most beautiful gravitational lens in the universe (see the HST-image). The dominating galaxies have grown by mechanisms like dynamical friction and even cannibalism among galaxies is common. Many clusters are named after the constellation in which they reside, like the afore mentioned Virgo and Coma clusters. Other examples are the  Perseus , Hercules and the Pavo-Indus cluster. A much larger number is named after George Abell, who found and numbered thousands of them in the fifties. Today they reveal such unprosaic numbers as the one mentioned above, where CL stands for cluster and the numbers designate the position in the sky.

Perseus Cluster of galaxies, 12inch f/6, Canon 50d, 2011

Chain of galaxies around NGC383, 12inch, f/6, Canon50d, 2011

This galaxy is also known as 3C31, a giant radio galaxy. Look for impressive images at http://www.cv.nrao.edu/~abridle/3c31xopt.htm



   NGC4038/39, Famous group of merging galaxies in Corvus, 8inch f/4.6, 05/16/99, jpeg 22k

This interacting pair of galaxies is called "The Antennae". It is so named because a pair of long tails of luminous matter, formed by the
gravitational tidal forces of their encounter, resembles an insect's antennae. The galaxies are located 63 million light-years away in the constellation Corvus. They are always too far south to be imaged from my home site. So it was quite clear, that this exiting object was one of my first targets, when I stayed in France, in May 99. Although the galaxies were not in the best position above the horizon, I was astonished to see so much detail and structure. It seems that my new, self build Newtonian is a sharp telescope. Of course I was not sure whether the antennae would come into view, but the night was good and you can see the result in the next image. This pair is also cataloged as Arp 244.

  Detail from image above shows the faint "antennae" of this pair

 

Stephan's Quintet, Compact group of galaxies in Pegasus,  Meade 14inch f/10, 10/10/2010, jpeg, 35k

Five closely grouped galaxies are visible in this image. The grouping is commonly known as Stephan's Quintet. Four of the galaxies
show essentially the same redshift suggesting that they are at the same distance from us. The large spiral below and right of the center actually has a smaller redshift than the others, indicating it is much closer. It is probably a foreground object which happens to lie along the line of sight to the more distant galaxies. Alternate names: NGC   7317,  7318B , 7318A, 7319, 7320,  UGC   12100 MCG  6-49- 40  CGCG 514- 62   HICK  92B  ARP 319 ?  VV 288 ?

 

The next image was made with the new ST8E-camera (1999). It provides a much larger field of view due to the large CCD, so it was possible to get M81 and M82 into the same frame.

  M81, M82, Group of galaxies in Ursa Major, 8inch f/4.6, ST8-E, 01/11/00, jpeg 43k

At a distance of 3.6 Mpc, the M81 is the next to our own Local Group of galaxies. It consists of several more members.wich are wide spread across the nothern sky. The next image shows HolmbergIX, a faint, close companion of M81. The image is enlarged from the one above.

  Holmberg IX, Fait companion of M81, jpeg 25k

  Arp 82 = NGC 2535/36, colliding galaxies in Cancer ca. 220 million lightyears away. NGC 2535 has a bright oval of star formation, perhaps even formation of new globular clusters is visible, 10inch f/4.6, 03/21/03, jpeg 180k, 5 images of 200sek exp.-time. Interesting facts and images of Arp 82 from far UV to deep infrared, made by the GALEX ( Galaxy Evolution Explorer) and Spitzer space telescopes on this website

  M60 and NGC4647 a close pair in Virgo, 10inch f/4.6, SBig ST-8e. Five images of 200 sec. were combined. 03/27/03, jpeg, 178k
Also visible in the full image are M59 (right), NGC4638 (middle) and several background galaxies.

NGC4490/85 in CVn, 10inch f/4.6, SBig ST-8e. Six images of 200 sec. were combined. 04/24/03, jpeg, 135k

  Arp 1 and Arp 285 in UMA, 10inch f/4.6, SBig ST-8e. Seven images of 200 sec. were combined. 02/25/03, jpeg, 146k

M66, M65 and NGC 3628, Leo's triplet, 8inch f/4.6, SBig ST8e, 01/28/00, jpeg 14k

 

  NGC 3190 (center)/85/87/93, Group of galaxies in Leo, 10inch f/4.6, ST-8E, 03/19/03, jpeg, 110k
This group is also known as Hickson 44.

  NGC 3745 /46/48/50/51/53/54, Copeland's Septet,Group of galaxies in Leo, 04/16/99,jpeg,10k

For a better designation look at this  finder chart.

  Center of the huge Coma Cluster of Galaxies, 04/05/03, jpeg, 176k
Almost every object in the above image is a galaxy. The Coma Cluster of Galaxies is one of the densest clusters known - it contains thousands of galaxies, where each of these galaxies contains billions of stars. Most galaxies in Coma and other clusters are ellipticals, while  galaxies outside of clusters are dominated by spiral forms. The nature of Coma's X-ray emission is still being investigated.

  M105,NGC 3389/84 (left to right), Group of galaxies in Leo, CG11 f/6.3, 03/11/99, jpeg, 14k

 

NGC 3389, M105, NGC 3384, Group of galaxies in Leo, 8inch f/4.6, ST8E, 01/28/00, jpeg 12k

 

  NGC 3605/07/08, Group of galaxies in Leo, 03/11/99, jpeg, 12k
There is another small uncataloged galaxy near the bottom of this image.
 

  NGC 4567/68 (bottom/top), The "Siamese Twins", group of galaxies in Virgo,03/11/99,jpeg, 6k
I have made a  drawing  of this group in 1997, while I stayed on La Palma island for holidays.

M51 and NGC 5195, Interacting galaxies in Canes Venatici, jpeg, 19k

Together with several fainter examples they form the M51 group.
There is also a drawing of these galaxies from 1997.

  NGC 4631 and small companion NGC 4627, Pair in Canes Venatici,12/17/98,jpeg,12k

It seems, that this large edge-on galaxy forms an interacting pair with NGC 4656 (not seen in this image).

  NGC 672 (right), IC 1727 and an uncataloged background galaxy in Triangulum, 12/17/98, jpeg, 33k

The following images are from July 30, 1998. Good, clear summer sky. The images of NGC 7479, 7814, 7385 are single shots of 100 second integration time. All others were made with 1 min exp. time. Five darks of 120 seconds and a flat field (average of 7 images) were used in all cases.
 

NGC 5981/82, Small group in Draco, 07/30/98, jpeg, 17k

NGC 5985/82, Small group in Draco, 07/30/98,  jpeg, 17k

NGC 7385..., Cluster of galaxies in Pegasus, 07/30/98, jpeg, 22k

Galaxy  NGC 7387, located at PA200 relative to brightest NGC7385, has highest  (in my collection)
RV  relative to the Local Group: 9909.512 km/second so far.
NGC 7385, Right ascension: 22h49m54.66s, Declination: +11 36' 31.7"
Remarks from the PGC (Principal Galaxy Catalog): PGC 069824
Effective surface brightness: 22.664 ñ .434 (magnitudes per square arcsecond)
Total B magnitude: 13.242 ñ .282
Galaxy RV relative to the Local Group: 8071.292 km/second
Major axis: 1.355ñ0.349 arcminutes
Alternate names:NGC    7385    UGC   12207    MCG  2-58- 17   CGCG 430- 15
 

The following images are from August 14, 1998.

 

Group of far away galaxies around NGC 6928 in Delphinus, 08/14/98, jpeg, 11k

NGC 6928, Right ascension: 20h32m49.63s, Declination: +09 55' 45.5"
Remarks from the PGC (Principal Galaxy Catalog): PGC 064932
Effective surface brightness: 21.932 ñ .490 (magnitudes per square arcsecond)
Total B magnitude: 13.232 ñ .180, Far infrared magnitude: 12.194
Galaxy RV relative to the Local Group: 4904.870 km/second
Major axis: 2.075ñ0.210 arcminutes
Alternate names: NGC    6928    UGC   11589    MCG  2-52- 17  CGCG 424- 21   IRAS20304+0945
 
 

The following image is from August 19, 1998.
 

Arp 331 , Distant chain of elliptical galaxies in Pisces, 08/19/98, jpeg, 19k

with 16.6mag UGC 679 left of center
NGC 383 (brightest G, lower left) Right ascension: 01h07m25.14s,Declination: +32 24' 46.5"
Remarks from the PGC (Principal Galaxy Catalog):PGC 003982
Effective surface brightness: 21.333 ñ .490 (magnitudes per square arcsecond)
Total B magnitude: 13.161 ñ .268
Galaxy RV relative to the Local Group: 5244.295 km/second
Major axis: 2.128ñ0.250 arcminutes
Alternate names: NGC     383    UGC     689    MCG  5- 3- 53  CGCG 501- 87   ARP     331 ?  KCPG     23B   VV      193 ?  4ZW      38 ?

NGC 7331, Group of galaxies in Pegasus, 08/19/98, jpeg, 18k

The following images are from December 17, 1998.

NGC 7332 and NGC 7339, Group of galaxies in Pegasus, 12/17/98, jpeg, 20k


NGC 1275 and many others, Cluster of galaxies in Perseus, 12/17/98, jpeg, 23k

NGC1275, Right ascension: 03h19m48.50s, Declination: +41 30' 45.0"
Remarks from the PGC (Principal Galaxy Catalog): PGC 012429
Effective surface brightness: 20.745 ñ .490 (magnitudes per square arcsecond)
Total B magnitude: 12.485 ñ .191,Far infrared magnitude: 11.183
Galaxy RV relative to the Local Group: 5476.540 km/second
Major axis: 2.570ñ0.681 arcminutes
Alternate names: NGC    1275    UGC    2669    MCG  7- 7- 63  CGCG 540-103   IRAS03164+4119

Mosaic, NGC 3079, NGC 3073 and the gravitational lens Q0957+561A/B, group of galaxies in Ursa Major, 12/17/98, jpeg, 5k
Right ascension: 10h01m58.18s, Declination: +55 40' 42.7"
Remarks from the PGC (Principal Galaxy Catalog): PGC 029050
Effective surface brightness: 21.166 ñ .490 (magnitudes per square arcsecond)
Total B magnitude: 11.265 ñ .328, Far infrared magnitude: 9.000
Heliocentric galaxy RV from neutral hydrogen: 1120.759 ñ 8.652 km/s
Heliocentric galaxy RV from optical observations: 1101.265 ñ 79.885 km/s
Galaxy RV relative to the Local Group: 1215.221 km/second
Major axis: 8.128ñ0.337 arcminutes
Alternate names: NGC 3079            UGC 5387            MCG 9-17- 10        CGCG 266- 8         IRAS09585+5555
 

Compare the image above with a x-ray   ROSAT image  of the same region.
 ( Abstract and Image from W.Pietsch, G.Trinchieri, and A.Vogler, NGC 3079: X-ray emission from the nuclear super-bubble and halo, Astronomy and Astrophysics 340, 351-370(1998).
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