Galaxies
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Deep View of Peculiar Galaxy Pair Arp 171
This very deep exposure shows the rarely imaged interacting galaxy pair Arp 171.
The pair consists of the lenticular (S0) galaxies NGC5718 and IC1042, and lie at the heart of a galaxy cluster 400 million light years away towards the constellation Virgo.
The galaxies were discovered by William Herschel in 1786 and later classified in Halton Arp's Atlas of Peculiar Galaxies under the category 'galaxies with diffuse counter-tails'. While Arp only saw the bright central core regions, this long exposure reveals the full extent of the tidal streams and shells of stars that have been flung far outwards from the merging cores.
These extended structures form when the cores of merging galaxies orbit around their common centre of mass in an ever tighter orbit while disrupting the halos of both galaxies and sending billions of stars into eccentric orbits. The halos of this pair of merging galaxies appear somewhat diffuse but the process can give rise to outward traveling density waves in the form of very distinct shells, such as those in NGC3923, until the collision eventually settles as one single large galaxy.
Several smaller members of the cluster can be seen around the merging galaxy pair, and in the background numerous other more distant galaxies can be seen. Near the top edge of the image lies a very distant galaxy cluster, visibly reddened by the cosmological redshift at very large distances.
Draped across the view is a thin veil of wispy filaments; ghostly structures that are known as galactic cirrus, or Integrated Flux Nebula (IFN). Only a few decades ago such structures were often removed in image processing, as they were thought to be instrument artifacts or image defects. However, these ultra faint patches of nebulousity are real and consist of thin traces of gas and dust which is not directly illuminated by stars but merely reflect the extremely faint combined glow of the Milky Way.
Image details:
Date: March - May 2022
Exposure: LRGB: 1935:280:280:250 mins, total 50 hours 15 mins @ -25C
Telescope: Homebuilt 12.5" f/4 Serrurier Truss Newtonian
Camera: QSI 683wsg with Lodestar guider
Filters: Astrodon LRGB E-Series Gen 2
Taken from my observatory in Auckland, New Zealand
