Object of the Week, November 18, 2017 - Zwicky's Pierced Galaxy, NGC 7732

[Howard B]

Interacting galaxy with NGC 7731
RA 23 41 33.852
Dec +03 43 29.83
Magnitude 14.25
Angular Size (arc minutes) 1.98 x 0.7

2808

NGC 7732 is directly south of the bright star in the image, with NGC 7731 immediately to the west of the star.

The only place I’ve seen this galaxy referred to as Zwicky’s Pierced Galaxy is in Interstellarum. It certainly got my attention and I couldn’t help imagining what unusual shape and/or astrophysical reason inspired this awesome name - so I observed it as soon as I could. Here’s my observation from the 2016 Oregon Star Party:

“So last night I found IC 1504 and thought it was Zwicky’s Pierced Galaxy (GREAT name and I’ve got to look it up when I get home). But this is the real deal, NGC 7731 and 7732. I looked up the DSS image of this pair in Megastar and it wasn’t obvious why it has such an evocative name, and visually it’s a low surface brightness elongated galaxy with an off-center area that’s brighter than the rest of the galaxy. I’m intrigued to learn more about how this seemingly run of the mill galaxy got its name. 476x, 21.68 SQM.”

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And through Jimi’s 48 inch in October 2016:

“Alright, now this really looks like a galaxy that should have a name. It has a mottled, granular look to its central axis and the brightest, widest end shoots off to the left of the FOV. It’s all low surface brightness though. 700x, 21.35 SQM”.

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To my surprise it looked rather ordinary in my 28-inch scope, but it does have considerable interest because it’s interacting with nearby NGC 7731. In Jimi’s scope it looked somewhat like a fat check mark. Photos show the hook area looking like an area active star formation area that’s possibly been perturbed by NGC 7731.

My guess is that the name comes from the “V” shape of the star forming area and its visual suggestion of piercing the side of the galaxy. But so far I haven't found any online references to Zwicky’s Pierced Galaxy - does anyone know where the name came from?

Regardless, these two galaxies make an attractive pair and the view is made even more lovely with a handful of field stars.

"GIVE IT A GO AND LET US KNOW"

[Uwe Glahn]

Very nice pair Howard.

Got an attempt last year under exceptional good condition in the High Alps. NGC 7731 shows a brighter, somewhat elongated central bar with a stellar nucleus and a faint halo around. NGC 7732 it self shows a small hook to the south. With averted vision it looks to me like a overlapping detail, like a second galaxy in front. Nice view.

27", 419x, NELM 7m0+, Seeing III
2813

[Steve Gottlieb]

NGC 7731 and 7732 are included in Zwicky's "Catalogue of Selected Compact Galaxies and of Post-eruptive Galaxies (http://ned.ipac.caltech.edu/level5/Sept02/Zwicky/frames.html)" (CGPG). Zwicky noted (https://ned.ipac.caltech.edu/level5/Sept02/Zwicky/cgpg11.html) NGC 7732 was a "Disrupted and badly 'dented' Sc." Furthermore, the appendix to the CGPG includes a photo of the pair and NGC 7732 is noted as a "Pierced" Sc spiral.

Wolfgang Steinicke and Richard Jakiel picked up on this comment and included NGC 7732 in their book "Galaxies and How to Observe Them" and nicknamed it "Zwicky's 'Pierced' Galaxy" in a table of peculiar or amorphous galaxies. Finally, the nickname is mentioned in Howard's article in the October issue of Sky & Tel (in a table of objects we observed on Jimi's telescope). There you go!

By the way, does anyone own a copy of Zwicky's rare "Red Book (http://adsabs.harvard.edu/abs/1971cscg.book.....Z)"?

[Howard B]

There you go indeed! Thanks Steve, this makes my day.

[obrazell]

Not surprised it is rare by the way he goes around accusing Sandage of plagiarising him and other insults in the paper.

Owen

[Steve Gottlieb]

Not surprised it is rare by the way he goes around accusing Sandage of plagiarising him and other insults in the paper.

Owen

Well, you know what he called other astronomers at Mt. Wilson -- spherical bastards! (didn't matter which way you looked)

But seriously, I think the reason it's hard to find is it was self-published in a small quantity.

[obrazell]

Well there is one here if you have $3000 https://www.abebooks.com/servlet/BookDetailsPL?bi=10314930565&searchurl=tn%3DCompact%2Bgalaxies%26sortby%3D17%26 an%3DZwicky&cm_sp=snippet-_-srp1-_-title1

:-)

Owen

[Paul Alsing]

Well there is one here if you have $3000 https://www.abebooks.com/servlet/BookDetailsPL?bi=10314930565&searchurl=tn%3DCompact%2Bgalaxies%26sortby%3D17%26 an%3DZwicky&cm_sp=snippet-_-srp1-_-title1

:-)

Owen

You would think that for $3,000 he could throw in free shipping :P

[Steve Gottlieb]

As the bookstore is in Pasadena, I wouldn't be surprised if that copy came from a disposal of unused books at the Mount Wilson observatory library!

[roragi]

Interesting galaxies for the next exit. They are within my scope 16'' but perhaps with less details than their sketches teach.