NGC 7320 Galaxy Group - Stephan's Quintet. (astroeyes)

Celestial hemisphere: Northern · Constellation: Pegasus (Peg) · Contains: NGC 7317 · NGC 7318 · NGC 7319 · NGC 7320

NGC 7320 Galaxy Group - Stephan's Quintet., astroeyes

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NGC 7320 Galaxy Group - Stephan's Quintet.

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NGC 7320 Galaxy Group - Stephan's Quintet.

Recorded on a very good night back in July, Stephan's Quintet consists of 5 interacting galaxies, NGC's 7317, 7318a, 7318b, 7319 and 7320.

All except 7320 have redshift velocities of between 5700 and 6700 km/s. 7320 has a redshift value of 800 km/s.

This means that 7317 to 7319 are about 8 times as far away from us than 7320 and therefore can not be physically connected. 7320 is the much bluer galaxy at bottom left in my image.

Halton Arp has challenged conventional wisdom and claims to have recorded a 'tail' stretching from 7320 away to the south east, which indicates, in his opinion, that there is interaction between the high and low redshift components of the Quintet. Indeed some images I have seen do appear to show a connection between 7320 and 7320c, the small galaxy above and to the left of the main group.

Additionally, the HST has located a quasar actually in front of the central core of 7319 (not visible in my image). The quasar has a redshift of 2.1 whereas the redshift of 7319 is 0.022, which should mean the quasar is about 100 times more distant but it appears in front of the quasar. Perhaps it is so bright that it can be seen shining through the galaxy's core but that seems unlikely to me.

My image shows the merest hint of a tail, no connection and no quasar; the group was discovered by Edouard Stephan in 1877.

23 x 3 minute exposures, altitude about 55 deg.

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NGC 7320 Galaxy Group - Stephan's Quintet.

NGC 7320 Galaxy Group - Stephan's Quintet.

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NGC 7320 Galaxy Group - Stephan's Quintet.

NGC 7320 Galaxy Group - Stephan's Quintet.

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