APOD: NGC 1316: After Galaxies Collide (2022 May 17)

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APOD: NGC 1316: After Galaxies Collide (2022 May 17)

Post by APOD Robot » Tue May 17, 2022 4:08 am

Image NGC 1316: After Galaxies Collide

Explanation: Astronomers turn detectives when trying to figure out the cause of startling sights like NGC 1316. Investigations indicate that NGC 1316 is an enormous elliptical galaxy that started, about 100 million years ago, to devour a smaller spiral galaxy neighbor, NGC 1317, just on the upper right. Supporting evidence includes the dark dust lanes characteristic of a spiral galaxy, and faint swirls and shells of stars and gas visible in this wide and deep image. One thing that >remains unexplained is the unusually small globular star clusters, seen as faint dots on the image. Most elliptical galaxies have more and brighter globular clusters than NGC 1316. Yet the observed globulars are too old to have been created by the recent spiral collision. One hypothesis is that these globulars survive from an even earlier galaxy that was subsumed into NGC 1316. Another surprising attribute of NGC 1316, also known as Fornax A, is its giant lobes of gas that glow brightly in radio waves.

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Re: APOD: NGC 1316: After Galaxies Collide (2022 May 17)

Post by Ann » Tue May 17, 2022 5:18 am

NGC 1316 and NGC 1317 are a fascinating pair of interacting galaxies!


NGC 1316 is a portrait of the aftermath of some sort of collision (which certainly involved NGC 1317 to the upper right of NGC 1316 in the APOD), whereas NGC 1275 is a portrait of the collision as it is happening (and the hapless smaller galaxy is no longer visible as an independent entity).

There is another galactic pair that is somewhat similar to NGC 1316/NGC 1317, namely NGC 474/NGC 470. There is a large elliptical that shows severe signs of upheaval, paired with a much more calm-looking spiral galaxy sporting a prominent ring:



The main difference between NGC 1316 and NGC 474 is that the tidal shells of NGC 1316 look rather messy, whereas in NGC 474 they look more elegant and "sculpted". And there are a number of "nested shells" in NGC 474.



A fascinating aspect of the NGC 1316/NGC 1317 pair is that NGC 1316 is classified as a (barred) lenticular galaxy, a galaxy with a disk but with little dust and no star formation, whereas NGC 1317 is classified as a barred spiral galaxy. But you can tell at a glance that these two galaxies are pretty much exactly the same color, the same shade of completely dominant yellow. Their color indexes confirm it: Both have a B-V index of +0.89! Their U-B indexes are also very similar, if not identical: +0.29 for NGC 1317 and +0.39 for NGC 1316.

The reason why NGC 1317 is a little more ultraviolet than than NGC 1316 is that NGC 1317 sports a nuclear ring of star formation, the only place in NGC 1317 where (any sort of substantial) star formation is taking place:

NGC 1317 detail from APOD 17 May 2022.png

Note that NGC 1317 is another of those two-ringed galaxies: There is a nuclear ring encircling the core and a larger ring encircling the galactic bar. There was another APOD showing such a two-ringed galaxy just a little more than a week ago. Do you remember?


Ann
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Re: APOD: NGC 1316: After Galaxies Collide (2022 May 17)

Post by orin stepanek » Tue May 17, 2022 12:05 pm

Ngc1316_Turgeon_1300.jpg
Maybe NGC 1316 may have some spiral arms or whats left of them!
I don't think NGC 1317 has much chance of victory here! David and
Goliath! :mrgreen:
lovely-puppy-portrait-picture-id92359506.jpg
Puppy looks lonely!
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Re: APOD: NGC 1316: After Galaxies Collide (2022 May 17)

Post by johnnydeep » Tue May 17, 2022 3:59 pm

Alright, can someone point out the "the unusually small globular star clusters, seen as faint dots on the image"? I'm not sure if those are the small orangish dots (green pointer lines) or the small blueish dots (yellow pointer lines):

NGC1316 globular clusters.png
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Re: APOD: NGC 1316: After Galaxies Collide (2022 May 17)

Post by Ann » Tue May 17, 2022 4:38 pm

johnnydeep wrote: Tue May 17, 2022 3:59 pm Alright, can someone point out the "the unusually small globular star clusters, seen as faint dots on the image"? I'm not sure if those are the small orangish dots (green pointer lines) or the small blueish dots (yellow pointer lines):

I don't we should look for orange-colored dots seen against a yellow galaxy when we look for globular clusters of NGC 1316. :no:

In Sky Catalogue 2000.0, Volume 2, there is a list of Milky Way globular clusters along with their B-V indexes. Generally speaking, most Milky Way globulars appear to have a B-V index of around 0.7 to 0.8. This is most likely slightly bluer than than the overall B-V index of the Milky Way itself.

Detail from Gaia Milky Way Omega Centuri.png
Milky Way vs. Omega Centauri by ESA:s Gaia telescope. Note Omega Centauri's
whitish color compared with the more reddish color of the Milky Way.


As you can see in the Gaia portrait of the Milky Way in the picture above, MW:s brightest globular cluster Omega Centauri is quite whitish in color, more so than most of the brightest parts of the Milky Way itself. I think, therefore, that the globulars of NGV 1316 will also show up as rather whitish dots, which are probably quite faint, too.

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Re: APOD: NGC 1316: After Galaxies Collide (2022 May 17)

Post by johnnydeep » Tue May 17, 2022 7:09 pm

Ann wrote: Tue May 17, 2022 4:38 pm
johnnydeep wrote: Tue May 17, 2022 3:59 pm Alright, can someone point out the "the unusually small globular star clusters, seen as faint dots on the image"? I'm not sure if those are the small orangish dots (green pointer lines) or the small blueish dots (yellow pointer lines):

I don't we should look for orange-colored dots seen against a yellow galaxy when we look for globular clusters of NGC 1316. :no:

In Sky Catalogue 2000.0, Volume 2, there is a list of Milky Way globular clusters along with their B-V indexes. Generally speaking, most Milky Way globulars appear to have a B-V index of around 0.7 to 0.8. This is most likely slightly bluer than than the overall B-V index of the Milky Way itself.

Detail from Gaia Milky Way Omega Centuri.png
Milky Way vs. Omega Centauri by ESA:s Gaia telescope. Note Omega Centauri's
whitish color compared with the more reddish color of the Milky Way.

As you can see in the Gaia portrait of the Milky Way in the picture above, MW:s brightest globular cluster Omega Centauri is quite whitish in color, more so than most of the brightest parts of the Milky Way itself. I think, therefore, that the globulars of NGV 1316 will also show up as rather whitish dots, which are probably quite faint, too.

Ann
So it seems you're saying that the real globular clusters are other even fainter more whitish dots than either the orangish or blueish dots I pointed out? If so, what then ARE the orangish and blueish dots? Mere foreground stars of different colors?
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Re: APOD: NGC 1316: After Galaxies Collide (2022 May 17)

Post by johnnydeep » Tue May 17, 2022 7:32 pm

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Re: APOD: NGC 1316: After Galaxies Collide (2022 May 17)

Post by Ann » Tue May 17, 2022 7:35 pm

johnnydeep wrote: Tue May 17, 2022 7:09 pm
So it seems you're saying that the real globular clusters are other even fainter more whitish dots than either the orangish or blueish dots I pointed out? If so, what then ARE the orangish and blueish dots? Mere foreground stars of different colors?
My guess is that most of them are stars. But a few of them look elongated and are therefore almost certainly galaxies.

Check out this portrait on NGC 1316/NGC 1317, which is more highly resolved than today's APOD. I think this might give you a better idea as to which dots are stars and which are galaxies, although I admit that it is still hard to see sometimes.

It looks to me as if there are a "swarm of faint white dots" "below" the main body of NGC 1316, in the fainter disk or tidal feature just below it. These faint dots are probably globulars.

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Re: APOD: NGC 1316: After Galaxies Collide (2022 May 17)

Post by Ann » Tue May 17, 2022 7:39 pm

johnnydeep wrote: Tue May 17, 2022 7:32 pm I did find these two pictures at odds with what I thought I was seeing - the left one is from a prior2005 APOD (https://apod.nasa.gov/apod/ap050404.html), and the right is from today's APOD. Both seem to be claiming that they show the whole galaxy, but clearly, the older one is but the tiniest center portion of today's! [ PS - one of these days I might figure out how to use the 'float' tags property. ]

From Explanation: How did this strange-looking galaxy form? Astronomers turn detectives when trying to figure out the cause of unusual jumbles of stars, gas, and dust like NGC 1316. A preliminary inspection indicates that NGC 1316 is an enormous elliptical galaxy that includes dark dust lanes usually found in a spiral. The above image taken by the Hubble Space Telescope shows details, however, that help in reconstructing the history of this gigantic jumble. Close inspection finds fewer low mass globular clusters of stars toward NGC 1316's center. Such an effect is expected in galaxies that have undergone collisions or merging with other galaxies in the past few billion years. After such collisions, many star clusters would be destroyed in the dense galactic center. The dark knots and lanes of dust indicate that one or more of the devoured galaxies were spiral galaxies. NGC 1316 spans about 60,000 light years and lies about 75 million light years away toward the constellation of the Furnace.

[img3]center of ngc 1316.JPG[/img3]

I think that many of the faint white dots seen scattered over the face of NGC 1316 in the Hubble image are globulars. My guess is that some of the brighter white dots are not globulars, but foreground stars, and that goes for more than the obvious star "above" the most prominent dust lane of NGC 1316. But I can't be sure.

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Re: APOD: NGC 1316: After Galaxies Collide (2022 May 17)

Post by AVAO » Tue May 17, 2022 8:24 pm

Ann wrote: Tue May 17, 2022 7:39 pm
I think that many of the faint white dots seen scattered over the face of NGC 1316 in the Hubble image are globulars. My guess is that some of the brighter white dots are not globulars, but foreground stars, and that goes for more than the obvious star "above" the most prominent dust lane of NGC 1316. But I can't be sure.

Ann
APOD Robot wrote: Tue May 17, 2022 4:08 am Yet the observed globulars are too old to have been created by the recent spiral collision. One hypothesis is that these globulars survive from an even earlier galaxy that was subsumed into NGC 1316.
Red circles shows the positions of the innermost Globular Clusters in the following paper: https://arxiv.org/pdf/1806.00316.pdf
"We confirmed the existence of multiple GC populations associated with NGC 1316, where the presence of a dominant subpopulation of very young GCs, with an average age of 2.1 Gyr, metallicities between -0.5 < [Z/H] < 0.5 dex and α- element abundances in the range -0.2 < [α/Fe] < 0.3 dex, stands out."

Obviously there are very old as well as very young globular clusters there. It's still a bit confusing for me...

Image
https://live.staticflickr.com/65535/520 ... 6a11_k.jpg
Jac Berne (flickr)

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Re: APOD: NGC 1316: After Galaxies Collide (2022 May 17)

Post by Ann » Wed May 18, 2022 4:01 am

AVAO wrote: Tue May 17, 2022 8:24 pm
Ann wrote: Tue May 17, 2022 7:39 pm
I think that many of the faint white dots seen scattered over the face of NGC 1316 in the Hubble image are globulars. My guess is that some of the brighter white dots are not globulars, but foreground stars, and that goes for more than the obvious star "above" the most prominent dust lane of NGC 1316. But I can't be sure.

Ann
APOD Robot wrote: Tue May 17, 2022 4:08 am Yet the observed globulars are too old to have been created by the recent spiral collision. One hypothesis is that these globulars survive from an even earlier galaxy that was subsumed into NGC 1316.
Red circles shows the positions of the innermost Globular Clusters in the following paper: https://arxiv.org/pdf/1806.00316.pdf
"We confirmed the existence of multiple GC populations associated with NGC 1316, where the presence of a dominant subpopulation of very young GCs, with an average age of 2.1 Gyr, metallicities between -0.5 < [Z/H] < 0.5 dex and α- element abundances in the range -0.2 < [α/Fe] < 0.3 dex, stands out."

Obviously there are very old as well as very young globular clusters there. It's still a bit confusing for me...

Image
https://live.staticflickr.com/65535/520 ... 6a11_k.jpg
Jac Berne (flickr)
Thanks, very interesting, AVAO!

Ann
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