Object of the Week April 10th, 2016: NGC 3432, the "indecisive" Arp galaxy

NGC 3432= Arp 206 = UGC 5986
RA: 10h 52' 30"
Dec: +36 37'
Type: Dwarf Spiral Galaxy (SB(s)m)
Dim:7'x2'
Mag: 11.5


This week’s object of the week is a relatively bright galaxy in a star-poor region in the constellation of Leo Minor.

I first observed this galaxy several years ago with my old 12” dob, but unfortunately I don’t have any notes from that occasion, except a checkmark on the observing list indicating “seen”. At the time I was just the “seen it, move on” kind of observer. My interest in this galaxy was rekindled after I observed it again last year as part of my effort to observe all Arp galaxies visible through my 18” dob.

Arp included this galaxy in his well known list of peculiar galaxies as entry 206, for being a galaxy with material ejected from nucleus. Indeed, in the photo of Arp’s Atlas, the galaxy does superficially resemble a more distant version of M82, a well known galaxy ejecting material from its nucleus. Yet, NGC 3432 appears as a paradox, for no active starburst activity has been observed. NGC 3432 is being disturbed by UGC5983, a small dwarf galaxy near its southwest end. Apparently, despite the interaction, no starburst activity has yet happened, indicating that the interaction with UGC 5983 has been rather recent. Astrophysicists suggest that usually there is a 400 million year lag between galaxy interaction and starburst activity, and NGC 3432 seems to be still in the lag phase. Hence my calling the “indecisive Arp galaxy”, for it is a galaxy which has yet to make up its mind for starburst activity!

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NGC 3432 image in Arp's Catalog of Peculiar Galaxies

Deep photos show that NGC 3432 is an edge-on system with lots of bright spots and dark lanes along its length, somewhat reminiscent of M82. In addition, on photographs a faint extension can be seen extending from the NE side of the galaxy, with a subtle central brightening, named MAC 1052+3640. On the SW end, the dwarf galaxy UGC 5983 can be readily seen in deep photos as a very diffuse roundish patch with a slightly brighter center. But what (from all these details) can be seen visually in a telescope?

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Deep photo of NGC 3432 by J. Schuder, http://www.pbase.com/image/143306089

My first observation of NGC 3432 with my 18” took place in February 2015. Under excellent conditions, NGC 3432 was a rather bright edge-on system, elongated 6-to-1, nicely framed by three 12th magnitude stars forming a tight triangle. At 275X in the 18” the galaxy appeared to extend from the base to the apex of the triangle. Two brighter patches adorn the galaxy, one centered on the eastern half of the galaxy, and the other, which is brighter, nearer the center of the galaxy. No distinct nucleus could be seen. A few arc-minutes to the west of NGC 3432 I could detect an extremely faint roundish patch, that I could hold steady only with averted vision. The position of this patch corresponds very nicely with UGC 5983. One important aspect of that observation was that at the time I had not expected to see another galaxy in the field, I confirmed it though by checking a DSS image after the observation. I did not though see the faint extension to the northeast.

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I re-observed the galaxy one week ago, but under so-and-so skies. NGC 3432 did appear more or less the same as in my first observation, but, despite the fact that I now knew of UGC 5983, I could not detect it. Apparently, this very low surface faint dwarf galaxy needs superb transparency to be detected.

I also observed NGC 3432 with my 5 and 6 inch achromatic refractors on a very transparent night. Despite the difference in aperture, the view was quite similar in both scopes. NGC 3432 appeared as a thin long streak of light tightly bounded in the triangle of the 13th magnitude stars. I could not detect UGC 6983 in either scope. I did not have a chance to observe NGC 3432 in my 4” apo, but I have no doubt it will be readily visible. As an aside, I also had a nice view of this galaxy in the 12.5” dob of NicosCY.

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Observations of this system by other observers are few and kind of disagree. Using a 17.5” dob, Steve Gottlieb has similar observations to mine, except that he finds the SW edge of NGC 3432 fainter. Also, he does not mention UGC 5983, so apparently he did not detect it. Barbara Wilson also does not mention UGC 5983 in her observations using a 20” dob, but Alvin Huey did detect UGC 5983 using his 22”. Huey also detected MAC 1052+3640 as a very low surface brightness patch. The most surprising observation though that I came across is by Stephen O’Meara in his “Secret Deep” book, where he mentions that he detected MAC 1052+3640 using a 5-inch refractor (but not UGC 5983).

So, NGC 3432, Arp’s 206th entry in his famous catalog, is a galaxy full of challenges for the dedicated observer. It’s agalaxy that abounds with detail and challenges for large light buckets, yet at the same time it is a galaxy that willingly unveils (at least some) of its secrets to the users of smaller instruments.

So, don’t be indecisive, and the next night you are out,

GIVE IT A GO AND LET US KNOW!

No one has ever observed this neck-breaking galaxy???? (Neck breaking as in it being 36N declination and myself living at 35N latitude LOL!)...

Not yet, but it's on my list!

I have :) Last year I had a look at these galaxies however I failed to notice that the south western blob I saw was another galaxy instead of a part of NGC 3432! My notes read:

At 320x visible as an elongated patch of light in between three bright stars. Two of those lie to the south west and the galaxy seems to touch one of these stars. To the north east the galaxy runs along the third stars and there lies a fourth, faint, star and the galaxy runs in between the third and fourth star. There lies a brighter patch in the galaxy on that side as well, which coincides with a star forming region. Further to the north east lies a detached part of the galaxy and another was lies east of the south tip. Very spectacular galaxy!

My older result was with my 16" a few "days" ago. See the sketch below.
My last is no week old and was a view trough a new 36" telescope. As you can imagine - stunning views. Although a quick and dirty observation the stunning thing was, that the connection between the main elongated and structured body and the NE knot was visible very easy. Aperture rules.

16", 225x, NELM 6m5+
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I saw this with my old 10 inch scope. My notes say Very faint misty glow around three stars.

Will have to go back again with my 16 inch.

Mark

I observed this galaxy March 2, 2016 from a friends house in Magdalena, NM (just under 7,000 feet elevation near the VLA) using my 25" f4 Obsession with Zambuto mirror. The conditions that night offered fairly clear skies, with average seeing, but the skies there were very dark. Even with less than best conditions the views were amazing.
I made the following log entry:
10 Ethos with Paracorr TypeII
Awesome view. A very slight bowl shape to this galaxy, looks kinda like an upside down plate. Really cool view. The galaxy extends out beyond the two stars that frame the one end. The galaxy extends out beyond those stars a little longer than the distance between the two stars. There is a mottling and widening in the arm opposite the two stars. There is a dim star that sits above it and a bright star below it.