This OOTW of this week is a faint and very challenging object even for 20" telescopes. However, it is a fascinating object and that's why I chose it.
The galaxy was already included in the MCG (Vorontsov-Velyaminov & Krasnogorskaja 1962, Vorontsov-Velyaminov & Arhipova 1963, 1964) and CGCG (Zwicky et al. 1961-68). A 1966 paper called "Identifications Of Radio Sources With Bright Galaxies" (J.L. Caswell and D. Wills, MNRAS 1967) cross-identifies the radio source 4C 35.06 with the optical galaxy MCG+06-07-034.
In 1971 Zwicky published a "Catalogue Of Selected Compact Galaxies And Of Post-Eruptive Galaxies" (link: https://ned.ipac.caltech.edu/level5/...ky/frames.html) in which he describes the system as "Group of six or more neutral compacts in luminous matrix. Plus several isolated compacts around it". Finally, George Abell included the galaxy and it's surroundings in his catalogue as number 407.
Let's have a look at what this galaxy actually looks like. Here are images from SDSS (left) and a false color image created by taking J, H and K band images from 2MASS
The images show at least 6 and up to 9 galaxies embedded in a halo as Zwicky also already noticed. In fact, Zwicky's catalogue contains a Palomar sky survey image identifying all 9 components. So, why could 6 or even all 9 galaxies be collapsing together? Well, this in fact already was proposed in 1982 by Scheider and Gunn (1982ApJ...263...14S) and they argue, based on spectroscopic and photometric observations, that very likely at least 8 and up to 11 (!) galaxies may collapse to a single cD galaxy on the time scale of about 2 billion years. They do, however, support the idea that at most 9 galaxies form the inner collapsing system. The other two galaxies lie to the west-south-west and south-south-west of this system and are considered cluster galaxies based on redshift measurements.
Fast forward to July 2016. A paper published by Biju et al. (https://arxiv.org/abs/1607.05080) tries to shed more light on the situation. They combine optical data taken from SDSS and 2MASS with radio observations done with the VLA (the Very Large Array in New Mexico, USA) and the GMRT (the Giant Meterwave Radio Telescope in India) which shows that most, if not all, 9 galaxies contribute to the radio emission of the system. This image combines the SDSS image with the 650 MHz GMRT data.
Moreover, the very deep GMRT radio data show twisted and kinked jets which suggests a perturbed AGN. The GMRT overlay on the SDSS image actually shows multiple radio cores. Further analysis of the radio data at different frequencies suggests that some parts of the outer lobes are quite old and do not get fresh particles injected. In short something very dynamic is going on here for sure and this system arguably is the most interesting example of a collapsing galaxy cluster in the sky!
So, what can we expect from this system visually? As I stated in the very first sentence of this article, the system is faint and challenging. The Biju paper gives these SDSS g magnitudes for the nine components (see the 2MASS image for which component is which) with the original Zwicky labels in brackets:
My notes from September 7, 2016, under SQM 21.6 skies using my 20" read very coarsely
"At 545x and 692x I see three (sometimes maybe even four) condensations inside a large halo. I am pretty sure I saw G1, G3 and G7 and I suspect that the fourth part may have been G5 but I only saw that component pop into view once or twice."
I remember that the observation was very difficult and that I intended to return to the object later that week but I never did.
As always,
"Give it a go and let us know!
Good luck and great viewing!"
Last edited by wvreeven; November 28th, 2016 at 07:03 AM.
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