Object Of The Week March 12, 2022 - Zwicky's Necklace

[wvreeven]

8 ZW 388, Zwicky's Necklace

Group of Galaxies

Virgo

RA: 14 15 06.786
DEC: -00 29 31.90

Mag: 17.0 and fainter

When Fritz Zwicky died, he left a huge amount of unpublished work. This contained a list of compact galaxies which he discovered after his 1971 Catalog of Compact Galaxies. This new list was published in 1975 as the Eighth List of Compact Galaxies. The list contains 496 entries and this OOTW is about number 388, also known as Zwicky's Necklace.

I came across this tiny, compact group of galaxies in the index of the Interstellarum DeepSky Atlas (IDSA). The atlas was created based on observing reports of many amateurs all over the world using a wide range of apertures. The atlas provides very useful information regarding which telescope it is visible in and, in case of emission nebulae, which filter likely is to work best. Given the faint magnitudes of the galaxies in this group, I am surprised and also excited to see it listed in the IDSA!

zwicky_s-necklace.jpg
SSDS DR15 image of Zwicky's Necklace.

Occasioanlly Simbad gets its IDs wrong, which is the case here as well since Simbad points slightly next to the actual group. See this link. The group is visible to the lower right of the Aladin preview. Using Aladin, all galaxies (and more) in a radius of 42 arcsec around the galaxy LEDA 1142006 (for which the RA and DEC are given at the top of this article) can be found. This totals 15 galaxies of which only 5 have known B and R magnitudes. The list can be seen here.

So, what is visible of this compact group? To be honest, I don't know! This is the first time I post an OOTW article about an object that I haven't actually observed yet myself. I had plans to go for it with my 20" but unfortunately I haven't been to Chile with this region of Virgo in an observable position in the sky since I learned about this group about half a year ago. However, I will go there again later this week and I intend to go and observe with my 20" for two weekends in a row while I am there and I will give this group a try. So I am curious to learn if anyone else has had a look at this group.


As always,

"Give it a go and let us know!
Good luck and great viewing!"

[Uwe Glahn]

That thing is tough Wouter, more of it later.

When you speak about the IDSA, I had to add the use of the Interstellarum Deep Sky Guide (IDSG), an companion which support the pure atlas with sketches and observing descriptions. Of course the VIII Zw 388 is also included.
Here in Europe, Wolfgang Steinicke introduce this group in an article in the year 2000 (VdS Journal 1/2000) and published it also in a book around 2004 (Praxishandbuch Deep Sky). I had the honor to observe it through Jimi's 48-inch Barbarella.

All in all a very difficult group. I add the group in my "Deep Sky Challenge" project and got three observations with different apertures so far. My research gives brightness o the members under 18bmag, beside the 16.8bmag bright PGC 3110345. To sum up the (only German written) descriptions, the 27-inch only shows the two brightest members. To see the necklace I needed at least a 36-inch and the 48-inch. But even then, not all single galaxies were seen.


sketch: 48", 610x, NELM 7m0+, Seeing III
8Zw388.jpg
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[Steve Gottlieb]

I observed the Necklace through Jimi's 48-inch back in May 2012 and similar to Uwe, I resolved four galaxies. Besides the faint magnitudes, the group is packed into a 1' circle with the ring itself only 40" across! So high power and good seeing are required, even in large apertures. I'm sure Jimi has observed this object several times, so perhaps he's caught it on a great night. Zwicky's Necklace has a similar redshift as AGC 1882 at distance of 1.75 billion light years (z = .137), so probably belongs to this rich cluster.

48" at 813x: Four members of Zwicky's Necklace were seen (two easily visible) with B magnitudes ranging from 16.8 (at east end) to 18.6. The entire group of >10 galaxies spans a length of 1'! The brightest member, PGC 3110345, is at the east end (just east of the actual ring) and it appeared very small, round, 10" diameter. A mag 16.6 star is 1' NNE and was convenient to use for fine focusing. PGC 1142006, a faint and round 8" glow was easily seen just 24" W. Two additional members, PGC 3304336 and 3304331 were very faint, popping in and out of view, at the north and west end of the ring.

[wvreeven]

Uwe, thanks for mentioning the IDSG and apologies for not mentioning it myself! I am currently in Spain, where I have the IDSA, but my copy of IDSG is in Chile. I am traveling there soon so I will for sure check it out!

[KidOrion]

Thanks to Uwe's wonderful sketch in the IDSG, I was inspired to seek this object out armed with a mere 20-inch. On a hazy June night with the Necklace well past meridian, I could not see any confirmable galaxies--not that I expected to--but I was able to tell in direct vision that something was at the location indicated on the POSS image.

Thanks for reminding me of this one, Wouter--back it goes onto the spring agenda!

[Jimi Lowrey]

I have observed this most unusual galaxy group many times over the years. I have found it best on nights of excellent seeing at powers of 800X and up. I will never forget the first time when the ring of galaxies suddenly appeared into view for a few seconds. I was so excited I let out a yell in the darkness from the tall ladder I was on. I was able to see the ring shape several times on this night it was quite exciting! On other nights it is tough see the fainter galaxies at all. The best views I have had is at 813X with a 6MM ZAO.

Like Uwe said this object is really tough. I would think that just to detect a glow from the combined galaxies would be an accomplishment.

[wvreeven]

I gave this group a shot tonight from Rio Hurtado in Chile using my 20" dob. Like KidOrion I suspected a glow at the location of the group at 197x. At 320x and 427x I could discern PGC 3110345 but nothing else. The size of the galaxy at those magnifications seems to indicate that I did see more than that galaxy at 197x but I am not certain. A tough one indeed! Having said that, I don't think that the transparency was great tonight. Cars passing in the distance produced beam-like glows, which usually isn't a good sign.

[akarsh]

I am yet to attempt this formidable group with my "mere" 18 inch, but I too have an observation from May 2016 with the same marvelous instrument through which (now) 4 out of the 6 observations reported here were made. I wrote of the conditions that night: "Excellent transparency, winds low".

4 galaxies were held steadily, with a fifth galaxy coming into view on a few occasions. I had three flashes of the overall ring structure. We were using a 8mm Delos eyepiece, which on Jimi's scope gives 610x.

[MelBartels]

The main thing is to make it to your eyepiece. Last night was average transparency at best and poor to medium seeing. My 30 inch with its 81 inch focal length is not the ideal telescope to look at a tiny grouping of distant galaxies. Nonetheless, I made it to my eyepiece.

Here's my sketch. Sometimes the little galaxies looked like scattered glittering dust and other times more like dim dark little charcoals.

NGC 5584 is on the way.

Bob was here with his 17.5 inch binos. We looked at a ton of stuff. I was most impressed with how milky smooth the IFN looked in his scope.

Zwickys Necklace NGC 5584.jpg

Mel Bartels

[akarsh]

The main thing is to make it to your eyepiece. Last night was average transparency at best and poor to medium seeing. My 30 inch with its 81 inch focal length is not the ideal telescope to look at a tiny grouping of distant galaxies. Nonetheless, I made it to my eyepiece.

Here's my sketch. Sometimes the little galaxies looked like scattered glittering dust and other times more like dim dark little charcoals.

NGC 5584 is on the way.

Bob was here with his 17.5 inch binos. We looked at a ton of stuff. I was most impressed with how milky smooth the IFN looked in his scope.

Zwickys Necklace NGC 5584.jpg

Mel Bartels

Amazing sketch, Mel! You must have had excellent seeing to see so much in a 30"!

Follow-up: I just noticed you mention the seeing to be "poor to medium". Perhaps our definition of excellent seeing is very different. Even though I live in coastal California, I have only rarely experienced our great stable seeing.

[MelBartels]

Ah yes, how to rate seeing. Rarely is it (seeing) good enough, so my typical response is that seeing is poor to medium. But yeah, being limited to 300x, maybe up to 500x during moments, is not great seeing in my book. I call that more along the lines of poor-medium seeing. As a good astro buddy once said, something along the lines of, the gods laugh at our entreaties for good seeing and delight in spinning the wheel of reality: one must meet the sky as it is, period! Mel.

[Jimi Lowrey]

That’s a great quote!