Object of the Week, March 28, 2021 - NGC 3628 Tidal Tail

Leo
Galaxy interaction tidal tail
Magnitude: faint
RA: 11 21 03
Dec: +13 34 56

Attachment 4272
Image by Mark Hanson, https://www.hansonastronomy.com/ngc-3628-mosaic


NGC 3628 is a well know edge-on galaxy in Leo, and is the northern most member of the Leo Triplet with M65 and M66 to its south. 3628 has been covered in previous OOTW’s, but not its tidal tail, which is our focus for this week.

3628’s tail is the result of its close encounter with M66 about 800,000 years ago when they came within about 82,000 light years of each other. The complete tidal tail extends about four times further to the east than shown in my sketch, and includes the Leo-TDG, a rare Tidal Dwarf Galaxy. More about that in a moment.

I’ve seen only the brightest portion of 3628’s tidal tail once with my 28-inch scope, and that was under good, but not great observing conditions:

“An excellent view, especially considering that it’s 2/3 of the way to the western horizon. The dark lane is prominent, and long, with the tidal tail readily seen. Low contrast except for the brightest part of the (core’s) central area, which also delineates the sharpest edge of the dark lane. 253x, 21.47 SQM.”

Attachment 4270 Attachment 4271

My sketch is a good approximation of what I saw, and I also remember my surprise at how easily visible the tidal tail and other faint features of 3628 were that night. On the other hand, I tried to observe it during the March 2021 new moon period with the same scope and a 22.00 SQM sky, but saw absolutely no trace of the tidal tail! After a bit of head scratching, I noticed that it was in the outskirts of a very bright Gegenschein, but I was still disappointed that I couldn’t detect even a hint of its glow.

So, is it surprisingly easy or surprisingly difficult to see? For now, the answer seems to be it’s both, and is probably a function of how sky darkness, transparency, the Gegenschein, and the observer interact. I’ll try again next month if the weather permits.

The Leo-TDG is located toward the much fainter eastern end of 3628’s tidal tail. It seems to have actually formed out of the tidal plume itself, making it a relatively rare object. Its location is easy to find because it’s just a few arc minutes north of the 15th magnitude background galaxy, IC 2787 – it’s between the two red lines in the Mark Hanson photo above. On the same night last month that I couldn’t see the tidal tail, I could barely see IC 2787, which may mean the bright Gegenschein really was reducing contrast in this area.

Jimi has seen the Leo-TDG with his 48-inch, and it seems possible other observers at a high-altitude site might have a chance to see it as well. I plan to keep trying, and hope many of you will too.

Give it a go and let us know!

Howard you might want to change the title to March 28th 2021 unless you are working a month ahead :-)

Perhaps that's because Howard also has an article on the Leo Triplet in the April issue of Sky & Tel.

Thanks Owen, I may never have seen that on my own. Unfortunately it seems I don't have access to correct the month to March because the title is outside the post - perhaps one of the moderators can change this?

Steve - you're probably right, but that still makes me a goof!

No worries. Taken care of

Quote:

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Originally Posted by Howard B

Thanks Owen, I may never have seen that on my own. Unfortunately it seems I don't have access to correct the month to March because the title is outside the post - perhaps one of the moderators can change this?

Steve - you're probably right, but that still makes me a goof!

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Thanks Dragan!

Howard do you know if Mel Bartels has any observations of NGC 3628 tidal tail with his super fast 25” scope. I would be interested in his results with the super fast 25” on this object.

Wonderful observation Howard - inspiring - must get back to the Triplet asap

Here's my obs from years ago - how time flies - with my 13" F3.0
The tail was at the limit but was clearly seen 100% of the time
The IFN surrounding particularly towards the bottom was fairly bright
It's a beautiful and subtle area with lots of varied detail

Attachment 4273

Mel Bartels

Wow Howard, I never though it was possible to see the faint tidal, but thanks to your OOTW I gave it a quick and dirty try last night shortly before moonrise. I doesn't know where to look at exactly (I even don't remember the roughly side of the tail), BUT it was clearly visible. Equipped with a 26mm Nagler, which gave me a field of around 40' with my 27-inch, I could see a faint and wide tail, starting at the northeast end of the NGC, running roughly until a triangle of 12mag stars. So it was visible around 0,5° length.
I have to revisit it more precisely and sketch it. And I will try the Leo-TDG also.

I tried last night (transp. 9/10, seeing 2-4 arcsec, SQM 21.8, object approaching meridian, elevation 700 m, aperture 20", magnification 150 with a wide-field ocular): Large apparent nebulosity running NE from E end of the galaxy, unconnected, S of three bright stars. Position and orientation do not match the photographic tail, match a group of subthreshold stars. Vm 16.4 star just beyond the E end of the galaxy is easily seen.

Hi all,

On 3th of April we had very good conditions despite of the fact that low clouds were passing. I could finally spot the brightest part of the tidal tail with my 14 inch Newton at 80x and 114x so far. I tried a 10 inch Newton also but nothing that I could spot. The brightest part is located between the two stars laying west of SAO 99572. The background is crowded of very faint stars there but at 168x I could see some of them and in fact they are to faint and very few, so the longitudinal glow that I saw could not caused by them.


Attachment 4283

I finally got a very nice night last new moon and give the galaxy a concentrated go.

What a fantastic object Howard and what a surprise to see the tidal tail. But it was clearly there. I only could see the brightest part. The first impression to see a longer tail was probably a false observation. Perhaps very similar like Ivan reported because of star empty regions and the dangerous contrast phenomenon between?

sketch: 27", 172x, NELM 6m5+, Seeing III
Attachment 4298
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