Object Of The Week November 27, 2016- UGC 2489

UGC 2489 - MCG+06-07-034, ZW V 311, 4C 35.06 a.k.a. Zwicky's Nonet

Group of up to 9 collapsing galaxies

Constellation: Perseus
RA: 03 01 51.4
DEC: +35 50 23

Mag: ~16.0

Size: 1.1'

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

Attachment 2355Attachment 2356

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.

Attachment 2357

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:

G1 (B) 15.84
G2 (A) 19.04
G3 (D) 16.00
G4 (C) 18.81
G5 (F) 17.93
G6 (E) 19.93
G7 (G) 16.34
G8 (H) -
G9 (I) 18.68

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!"

Great ultra-compact galaxy group!

I've only looked at the field once, back in 1999, while doing a quick survey of AGC 407 in a 17.5". UGC 2489 was noted as "faint, elongated glow with an irregular surface brightness, ~1' in length". I was only using 220x, not enough to possibly resolve the tight components. UGC 2489 has been on my "reobserve" list for years, but I never got back to it.

Other galaxies I picked up during the 1999 observation included UGC 2491, 2493 and 2494. But checking later, UGC 2491 lies in the foreground and is a member of the NGC 1167 group (LGG 080). UGC 2493, perhaps the brightest member of AGC 407, is a double system (actually an overlapping pair on the SDSS) - another challenge while in the area!

Great object. I observed this group 7 years ago when I was doing Zwicky's Red Book catalog. My brief notes say "six seen, really cool group,Nice!" The note nice! means for me to look at it again. I guess now would be a good time to revisit it :D. The fainter galaxies are going to take a night of great seeing and transparency.

Thanks for mentioning UGC 2491, UGC 2493 and UGC 2494, Steve. I didn't observe UGC 2494 because it seemed to lie outside of Abell 407, but I did observe UGC 2491 ("At 320x reasonably large with a slightly brighter central region.") and UGC 2493 ("At 320x seen the two nuclei of the two galaxies that form this one.") that same night.

A very intriguing group; I'll have to give this one a try if the rain ever stops here. (Almost eight weeks straight of clouds here.)

So this one's a nonet. We have triplets and trios (Wild's Triplet, Zwicky's Triplet, the Leo Trio), quartets (the Grus Quartet), quintets (Stephan's Quintet), sextets (Seyfert's Sextet), septets (Copeland's Septet), and a nonet. Any octets?

I had a look at UGC 2498 last night with the 82". Transparency was excellent, but seeing was mediocre (~2 seconds). At low power (402x), the six brightest components (G1,3,4,5,7,9) were distinct and fairly bright. With an increase in power to 757x, G2 began popping in sporadically. At 1282x, G2 was visible most of the time, and G6 popped in occasionally. Due to the seeing conditions, G7 was smeared out fairly wide, and G8 was not detected, even as a bulge on G7. In all, 8 of 9 components seen. It will take a night with excellent seeing to determine whether G8 is achievable.

Nice group. I visited last nights with my 27-inch (733x). G7 brightest member and a little bit separated from the nebulous glow. Glow itself visible as a difficult to separate but clearly visible G1/G3 line. Glow bents to SW with faint G4 at its end. G9 popping in and out of view and because of the separated position easier than expected. G5 hardest direct member because of the near position to the disturbing glow of G1/G3/G4. Very difficult to see and only popping.
N and NE three more galaxies visible.

I add a sketch when ready.

:shocked: :shocked: :shocked:

Thanks for sharing that observation with us, Jim. I am sure you are the first and only person on Earth to have seen that many components in this galaxy with your own eyes!

Just want to add the sketch of the group.

27", 733x, Seeing III, NELM 7m0+
Attachment 2393

This is not the only nonet, though -- WAY easier, the 9 galaxies around M84, M86 and the Eyes are sometimes called the "nonet". Visible in an 8" from mediocre skies :D

Came here to see if anyone had tried to see the combined light at least with an 18". I just put it on the list :scared:

Also adding an old observation through Jimi's 48". October 2014.
Attachment 4183

Quote:

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Originally Posted by akarsh

Came here to see if anyone had tried to see the combined light at least with an 18". I just put it on the list :scared:

Also adding an old observation through Jimi's 48". October 2014.
Attachment 4183

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12/18/22 UGC 2489 21.3mpsas
In my 10” SCT at 200x, the small clump known as UGC 2489 in AGC 407 wasn’t very hard to see. At 450x and above in my 16”, I can see two or three member galaxies. Shouldn't be a problem for someone under a darker sky to see it with a single-digit aperture telescope.

Scott H.