Object of the Week, June 19, 2022 - NGC 6670 "The Poster Girl"

[Uwe Glahn]

NGC 6670 (PGC 62033, UGC 11284, CGCG 301-31, MCG 10-26-44, 7ZW 812)
size: 1.1' x 0.5'
magnitude: 14.3vmag
Pair of interacting galaxies in Draco

NGC 6670A (NGC 6670-2, NGC 6670E)
18h33m37.72s, +59d53m22.8s

NGC 6670B (NGC 6670-1, NGC 6670W)
18h33m34.09s, +59d53m17.6s

No simply object as usual by me today, but a more interesting pair when it comes to form a beauty in the sky - the peculiar pair of interacting galaxies in Draco NGC 6670 witch shows slightly different edge-on angles and some starburst activities. In 2008 the pair becomes fame as a "Poster Girl" (https://commons.wikimedia.org/wiki/File:Galaxies_Gone_Wild!.jpg), a compilation of interacting pairs illustrated by the HST.

Discovered at July 31, 1886 by Lewis Swift, he describes the not resolved pair as "extremely faint, small, considerably elongated and extremely difficult". He uses a 16" Refractor at Warner Observatory. So, in summery a later discovered visual object with a relative large and modern telescope from which we can conclude some observations better today than from the more unknown speculum mirrors.

Not unusual enough I found an for me uncommon designation. Because Swift did not record a separation, we found an "1" and "2" in the NGC. Even so NED divided the both main galaxies in an "A" and "B". New to me was the "E" and "W", which stands for the sky direction "west" and "east". NED also accepts theses abbreviations and science took them over. Anyone who knows the origin?

Little science is known about this beauty. Both are located around 400 million light-years away from Earth and seems to have one close encounter and is now in the early stages of a second. Wang et al [2001AJ....122..140W] (https://arxiv.org/pdf/astro-ph/0103280.pdf) classify the galaxy as a luminous infrared galaxy (LIRGs) and discovered long H I tidal tails and concluded the current interacting status. They also suggests active star formation in the nuclear regions of the galaxies.

In the 20-inch telescope galaxy E is visible with direct vision as a 3:1 elongated and slightly concentrated object with a very faint spot at the eastern end. W is visible as a faint, structureless pin. The 27-inch shows similar details while the W seems to be a little bit bend.

DSS blue, 30'x30'
4754

HST (N up) by NASA, STScI, ESA
4755

sketch: 27", 419x, NELM 6m5+, Seeing IV
4756
home (http://www.deepsky-visuell.de/Zeichnungen/NGC6670-Gruppe.htm)

But what could you see, give it a go and let us know.

[akarsh]

I’m surprised that this pair neither has an Arp nor a VV designation. Great OOTW, time to put it on the list.

[obrazell]

It does have the VV designation 1875 in the extended VV catalogue

[akarsh]

Thank you for this object, Uwe.

I gave it a go with my 18" f/4.5 under the pristine skies of the Warner mountains of north-eastern California late last month, on June 26 2022.

Using a 6mm Delos eyepiece (344x 1.3mm ExPu), both galaxies appeared almost equally bright and made an exceptional pair. I could detect their elongations, making about a 135° angle with each other. Using a 5mm Pentax, one of the galaxies (NGC 6670A) appeared brighter than the other (NGC 6670B), the latter being very intermittently visible. I was unable to resolve the "knot" at the eastern end of NGC 6670A, that is separated from the rest of the galaxy with the dust lane. I believe this is what Uwe has captured in his sketch as a stellar point.

I'm surprised that this object was discovered in a 16", given that it was not easy to observe in my 18", even from very good skies! I did have some haze and rather high airglow, but I otherwise had Bortle 1 skies and an elevation of 7300 ft.

BTW, I'm given to believe that the A-B-C designations attached to NGC and IC objects are later introductions by Dr. Harold Corwin (perhaps most famous for the RC3 catalog along with de Vaucouleurs as well as the Abell-Corwin-Olowin revision of Abell's 1958 catalog). Steve Gottlieb would know for sure.

[Uwe Glahn]

Thanks for your posting of your observation Akarsh.

Good to know what is visible through a 18-inch situated under pristine skies.

But your are right - Swift's observation is in fact astonishing. While he uses a modern 16-inch refractor (with some light loss because of missing coatings) he already was suffering of starting light and air pollution near the centre of Rochester. But his good eyes and his huge experience compensate this difficulties.