Quasar HE 1013-2136
Since some time, astronomers have therefore been searching for clear evidence for a connection between gravitational interaction and the quasar phenomenon. However, quasars are very bright objects and their light easily outshines all nearby objects. Any companion galaxies and structural features that may indicate interaction are therefore hard to detect.
While observations with the Hubble Space Telescope (HST) have much improved our knowledge of the interaction-activity connection in some relatively nearby quasars, it has been difficult to probe the same phenomenon in more distant quasar environments. Such studies clearly require larger telescopes.
The observations of the quasar HE 1013-2136 presented here result from a new programme that addresses this issue at earlier cosmic epochs. This 17-mag object is seen in the southern constellation Hydra (The Water Snake) and is located at a distance of about 10 billion light years (the redshift is z = 0.785)
PR Photo 20a/01 shows an image of HE 1013-2136 and its immediate surroundings, obtained with the FORS2 multi-mode instrument at the 8.2-m VLT KUEYEN telescope under very good seeing conditions. The image resolution is about 0.6 arcsec, or about 10,000 light-years at the distance of the quasar. The image has been further sharpened by means of image processing software (the Lucy algorithm) in PR Photo 20b/01 , now also showing the distribution of objects very close to the bright quasar image. This impressively illustrates the light gathering and resolution power of the VLT.
The quasar is the point-like object at the center of the images. It is embedded within a complex structure that mainly consists of two arc-like and knotty tails extending in different directions. Such tails are well-known from nearby galaxy interactions, cf. NGC 6872/IC4970 and are a consequence of tidal forces in the gravitational field of the galaxies.
The astronomers believe that the two tidal tails result from a dramatic interaction between the quasar host galaxy and one or more of the close companion galaxies. The longer, southern tail extends over more than 150,000 light years, one-and-a-half times the diameter of the Milky Way. In many respects this distant interaction resembles the well known Antenna Galaxies (see the Hubble image ), where two nearby galaxies distort each other in a gravitational dance.
In the case of HE 1013-2136 , a number of knots can be seen along both tidal tails. In particular, the object just below the quasar image, most easily seen in the sharpened image (PR Photo 20b/01 ), lies at a projected distance of only 20,000 light years. This is about two-thirds of the distance from the Earth to the center of the Milky Way galaxy. This object is most likely a companion that is interacting with the quasar host.
Recent observations of nearby quasars have revealed that they mostly reside in elliptical galaxies . Numerical simulations suggest that such galaxies can be formed by successive mergers of spiral galaxies.
Klaus Jäger and his colleagues point out that "with the VLT observations of HE 1013-2136 , we may be directly witnessing such a dramatic merger of galaxies. The special significance of this observation is the great distance and hence the comparably early time at which this happens, when the Universe was about one third as old as it is now". He adds: "This particular galaxy will most probably evolve into the same type of elliptical quasar host galaxy that we observe much nearer to us, that is, at much later times".
Text from: http://www.eso.org/outreach/press-rel/pr-2001/pr-13-01.html