This time we stopped on is a small object of 3.4' of arc by 1.7' of arc...
NGC 520 ou Arp 157We present a couple of Galaxies in interaction in Pisces : NGC 520 (Arp 157) showing all the kinematics of galactic mergers.
Only portions of the original galaxies are somewhat identifiable. A very large tidal tail loops away from the central mayhem. These galaxies are colliding around 100 million light years away from us and this one in particular is one of the brightest examples in the sky.
Arp 157 (NGC 520, UGC 966, VV 231 and others) is a galaxy train wreck. Arp has this one in his ‘Disturbed with interior absorption’ class.
This irregular galaxy is the result of the merger of two spirals approximately 105 million light-years away in Pisces. Note the faint tidal tail going to the north towards faint UGC 957.
They were discovered by astronomer William Herschel on 13 December 1784.
Halton Arp called this the second-brightest very disturbed galaxy in the sky, and it is as bright in the infrared and radio bands as the Antennae Galaxies. Simulations indicate this object consists of two galactic disks that began interacting about 300 million years ago. The system is still in an early stage of its merger, showing two separate velocity systems in the spectra, and two small tails. Two galactic nuclei have been detected,and one is an H II nucleus.
One possible interpretation is that a smaller, irregular galaxy (represented by the crescent-shaped fragment S of the larger galaxy’s dust lane) has side-swiped the larger galaxy. Both have very bright central regions and they meet at an angle of about 10°. The main galaxy’s dust lane is highly disturbed: it is a broad oval in the eastern portion, narrowing as it crosses the core, then broadening again, defining a faint plume of material emerging towards the W. A prominent plume of material emerges from the core, broadening and curving towards the SSE. In a moderate-aperture telescope, the galaxy is bright and of a peculiar form. The main envelope is fairly even in surface brightness. The western end is very slightly broader than the middle. The eastern tip forks into two, with the main body curving slightly to the E, while a short spur juts off to the ESE. Overall, the envelope is quite well defined and is elongated ESE–WNW. Herschel’s 13 December 1784 discovery comments say only that the object is: ‘Extremely faint, considerably large, extended.’ Radial
The main galactic component is being viewed edge-on, making it fainter in the optical band. The secondary component is brighter but less massive than the main, and is located to the northwest. They are separated by a dark lane of dust. The region of the galaxies outside their nuclei experienced a period of increased star formation roughly around the time they began to interact."velocity: 2353 km/s. Distance: 105 mly.Diameter: 137 000 ly.
On this image we can also see :
- 2 blueish objects : a galaxy in couple of Galaxies (upright) MCG00-04-124 and a galaxy in a cluster of galaxies UGC 957 (bottom left)
- A galaxy near NGC 520 : LEDA 5195 de mag 17.46
The image is processed in drizzle, cropped but not entirely restored to its original size.
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