2 Attachment(s)
Object of the week 16th October 2022 - NGC 7679 - Arp 216
NGC 7679
Arp 216
VV 329
Galaxy
Class SB0 pec
Pisces
R.A. 23h28m46.7s
Dec. +03°30'41" (2000)
Magnitude: 13.40 B
Size: 1.2' x 0.8'
The starburst galaxy NGC 7679 in Pisces was first discovered by Heinrich d’Arrest in 1864 using an 11” refractor.
Classified as a barred lenticular galaxy it is also classed as a luminous infra-red galaxy or LIRG. It has an AGN
in the form of a Seyfert type but it is odd enough that it cannot be classified as a Type 1 or 2. It has been
classified as both but most recently it is suggested to be a Seyfert Type 2. It is associated with the spiral
galaxy NGC 7682, also discovered by d’Arrest, but two years earlier in 1862, although some sources suggest
they were both discovered in 1864. The two galaxies are interacting and were included both in Arp’s catalogue
as Arp 216 and Vorontsov-Velyaminov’s catalogue as VV 329. The Arp classification falls into the group
galaxies with adjacent loops. The two galaxies have a neutral hydrogen bridge connecting them. The star
burst in NGC 7679 takes place in the circumnuclear region and it is unusual as lenticular galaxies do not
usually contain enough gas for star formation to take place. In this case the star formation is thought to
have taken place about 10 million years ago.
Attachment 4898
Image credit SDSS
The gravitational tides raised by the interaction have dragged
two plumes of material out of NGC 7679. The two galaxies probably had a close pass, perhaps 500 million
years ago and are currently separated by perhaps 97kpc. In comparison NGC 7682 does not appear to show
much disturbance. It is possible that the star plumes seen in NGC 7692 maybe the remnants of a merger with
another galaxy rather than as a result of the interaction with NGC 7682. NGC 7682 is also classified as a type
2 Seyfert.
Attachment 4899
HST image credit, NASA/ESA and Judy Schmidt
The pair are thought to be about 190 million light years away. The galaxy seen in the arms of
NGC 7679 is a background object. There is a third galaxy in the field, UGC 12628, which given its redshift
may be part of the same group. There is also a tight 10th magnitude double star Bu 1222, discovered by
S.W. Burnham, about 5’ NW of NGC 7679.
The pair is pretty close so a high power eyepiece will be best when observing them. They should not be that
difficult in 40cm (16") telescopes and both galaxies should show a faint stellar core. It maybe that the plumes
will be visible in the very largest telescopes in amateur hands
As always, give it a go and let us know!!
