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APOD: NGC 1316: After Galaxies Collide (2022 May 17)
Posted: Tue May 17, 2022 4:08 am
by APOD Robot
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.
Re: APOD: NGC 1316: After Galaxies Collide (2022 May 17)
Posted: Tue May 17, 2022 5:18 am
by Ann
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:
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
Re: APOD: NGC 1316: After Galaxies Collide (2022 May 17)
Posted: Tue May 17, 2022 12:05 pm
by orin stepanek
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!
Puppy looks lonely!
Re: APOD: NGC 1316: After Galaxies Collide (2022 May 17)
Posted: Tue May 17, 2022 3:59 pm
by johnnydeep
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):
- NGC 1316 Globular Clusters?
Re: APOD: NGC 1316: After Galaxies Collide (2022 May 17)
Posted: Tue May 17, 2022 4:38 pm
by Ann
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.
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.
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
Re: APOD: NGC 1316: After Galaxies Collide (2022 May 17)
Posted: Tue May 17, 2022 7:09 pm
by johnnydeep
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.
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?
Re: APOD: NGC 1316: After Galaxies Collide (2022 May 17)
Posted: Tue May 17, 2022 7:32 pm
by johnnydeep
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. ]
- center of ngc 1316.JPG (13.86 KiB) Viewed 2841 times
Re: APOD: NGC 1316: After Galaxies Collide (2022 May 17)
Posted: Tue May 17, 2022 7:35 pm
by Ann
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.
Ann
Re: APOD: NGC 1316: After Galaxies Collide (2022 May 17)
Posted: Tue May 17, 2022 7:39 pm
by Ann
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. ]
[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.
Ann
Re: APOD: NGC 1316: After Galaxies Collide (2022 May 17)
Posted: Tue May 17, 2022 8:24 pm
by AVAO
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
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...
https://live.staticflickr.com/65535/520 ... 6a11_k.jpg
Jac Berne (flickr)
Re: APOD: NGC 1316: After Galaxies Collide (2022 May 17)
Posted: Wed May 18, 2022 4:01 am
by Ann
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
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...
https://live.staticflickr.com/65535/520 ... 6a11_k.jpg
Jac Berne (flickr)
Thanks, very interesting, AVAO!
Ann