APOD: Stellar Streams in the Local Universe (2024 Sep 27)

[APOD Robot]

Stellar Streams in the Local Universe

Explanation: The twenty galaxies arrayed in these panels are part of an ambitious astronomical survey of tidal stellar streams. Each panel presents a composite view; a deep, inverted image taken from publicly available imaging surveys of a field that surrounds a nearby massive galaxy image. The inverted images reveal faint cosmic structures, star streams hundreds of thousands of light-years across, that result from the gravitational disruption and eventual merger of satellite galaxies in the local universe. Such surveys of mergers and gravitational tidal interactions between massive galaxies and their dwarf satellites are crucial guides for current models of galaxy formation and cosmology. Of course, the detection of stellar streams in the neighboring Andromeda Galaxy and our own Milky Way also offers spectacular evidence for ongoing satellite galaxy disruption within our more local galaxy group.

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[raschumacher]

For your inner cosmos listening pleasure:

https://en.wikipedia.org/wiki/Musical_Starstreams

[Bartolo]

What were the criteria used to determine the contour in which the image of the galaxy at the center is inverted?

[johnnydeep]

What were the criteria used to determine the contour in which the image of the galaxy at the center is inverted?

Contour?

[Chris Peterson]

What were the criteria used to determine the contour in which the image of the galaxy at the center is inverted?

I'd say they just eyeballed the visible edge of the galaxy, which in all cases is pretty sharp, manually drew a mask, and inverted outside of that mask. Any rigorous use of intensity profiles to define the galaxies would risk masking stream structures, as well.

[johnnydeep]

What were the criteria used to determine the contour in which the image of the galaxy at the center is inverted?

I'd say they just eyeballed the visible edge of the galaxy, which in all cases is pretty sharp, manually drew a mask, and inverted outside of that mask. Any rigorous use of intensity profiles to define the galaxies would risk masking stream structures, as well.

The text said it was a composite, so I took that to mean that it was just an overlaying of an original color image with an inverted b/w version of that same image. Not plausible?

[Chris Peterson]

What were the criteria used to determine the contour in which the image of the galaxy at the center is inverted?

I'd say they just eyeballed the visible edge of the galaxy, which in all cases is pretty sharp, manually drew a mask, and inverted outside of that mask. Any rigorous use of intensity profiles to define the galaxies would risk masking stream structures, as well.

The text said it was a composite, so I took that to mean that it was just an overlaying of an original color image with an inverted b/w version of that same image. Not plausible?

Sure. Either way it's a masking operation, though, and almost certainly a subjective, manual one.

[johnnydeep]

I'd say they just eyeballed the visible edge of the galaxy, which in all cases is pretty sharp, manually drew a mask, and inverted outside of that mask. Any rigorous use of intensity profiles to define the galaxies would risk masking stream structures, as well.

The text said it was a composite, so I took that to mean that it was just an overlaying of an original color image with an inverted b/w version of that same image. Not plausible?

Sure. Either way it's a masking operation, though, and almost certainly a subjective, manual one.

Ok. I was thinking that the inverted version would show the streams but the original image wouldn't, but that's clearly wrong. And now looking closer, it's also pretty obvious that some masking was used to limit how far the non-inverted image extends.

[Ann]

It is hard for me to say much about the POD in itself, because the picture is quite large and many of the galaxies are in fact rather distant and small in the sky. Several of them are 14th magnitude, and I have been unable to find any useful pictures of meny of them. (Such as, for example, ESO 199-012.)

But there exists a gorgeous Hubble image of NGC 922:

NGC 922. Isn't it gorgeous? Note that you can actually see a dusty brown jet shooting away from the core(?) towards the top of the image. Credit: NASA, ESA.

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NGC 1097 is another very interesting galaxy. Three of its jets are clearly visible in this beautiful image by Mark Hanson:

NGC 1097. It's a lovely image. You can see the small companion galaxy at upper right, NGC 1097A, which is clearly responsible for stirring things up in the large galaxy. Credit: Mark Hanson.

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But let's look at some other interacting galaxies, shall we? There is so much beautiful chaos and order and birth and death in the realm of interacting galaxies!

Arp 256, spiral galaxy pair in the early stages of colliding and merging. Credit: NASA, ESA, the Hubble Heritage.

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Elliptical galaxies can do it, too:

Elliptical shell galaxy NGC 474 and spiral companion NGC 470. Credit: Mark Hanson.

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And make room for the loveliest of galaxies, the Bird or the Tinker Bell of the local universe!

The other Tinker Bell.

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Using ESO's Very Large Telescope, an international team of astronomers has discovered a stunning rare case of a triple merger of galaxies. This system, which astronomers have dubbed 'The Bird' - although it also bears resemblance with a cosmic Tinker Bell - is composed of two massive spiral galaxies and a third irregular galaxy.

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The formal name of the galactic bird or fairy is ESO 593-IG 008. Let's enjoy the sight of it taking flight!

Ann

[johnnydeep]

To me, NGC 1097A looks far more like a distant unrelated (and undisrupted) background galaxy than an interacting companion of NGC 1097. But all the sources I've found seem to disagree with me.

[Ann]

To me, NGC 1097A looks far more like a distant unrelated (and undisrupted) background galaxy than an interacting companion of NGC 1097. But all the sources I've found seem to disagree with me.

NGC 1097 and NGC 1097A. Credit: Mark Hanson.

---

NGC 1097 and NGC 1097A have much the same radial velocities, meaning that they are at much the same distance. They could indeed be entangled inside one another, but they will have their own velocity due to their interactions, which will suggest that they are at somewhat different distances. even though they are not.

The reason why NGC 1097A looks so undisturbed is almost certainly because it hasn't got any "arm fluff". It may very well have had arms before it started interacting with NGC 1097, but it has lost its arms since then. Therefore it looks undisturbed.

Take a look at "The Eyes", NGC 4438 (which has arms) and NGC 4435 (which has not):

NGC 4438 and NGC 4435 are interacting. But only NGC 4438 looks disturbed,
because it has arms. NGC 4435 has not. Credit: KuriousGeorge.

Ann

[johnnydeep]

To me, NGC 1097A looks far more like a distant unrelated (and undisrupted) background galaxy than an interacting companion of NGC 1097. But all the sources I've found seem to disagree with me.

NGC 1097 and NGC 1097A. Credit: Mark Hanson.

---

NGC 1097 and NGC 1097A have much the same radial velocities, meaning that they are at much the same distance. They could indeed be entangled inside one another, but they will have their own velocity due to their interactions, which will suggest that they are at somewhat different distances. even though they are not.

The reason why NGC 1097 looks so undisturbed is almost certainly because it hasn't got any "arm fluff". It may very well have had arms before it started interacting with NGC 1097, but it has lost its arms since then. Therefore it looks undisturbed.

Take a look at "The Eyes", NGC 4438 (which has arms) and NGC 4435 (which has not):

2019-05-07_5cd1d0208a20f_TheEyes_S1_HVLG_SS1040_CBS_HVLG_Curves_s[1].jpg

NGC 4438 and NGC 4435 are interacting. But only NGC 4438 looks disturbed,
because it has arms. NGC 4435 has not. Credit: KuriousGeorge.

Ann

Ok, thanks.

[AVAO]

To me, NGC 1097A looks far more like a distant unrelated (and undisrupted) background galaxy than an interacting companion of NGC 1097. But all the sources I've found seem to disagree with me.

NGC 1097 and NGC 1097A. Credit: Mark Hanson.

---

NGC 1097 and NGC 1097A have much the same radial velocities, meaning that they are at much the same distance. They could indeed be entangled inside one another, but they will have their own velocity due to their interactions, which will suggest that they are at somewhat different distances. even though they are not.

The reason why NGC 1097 looks so undisturbed is almost certainly because it hasn't got any "arm fluff". It may very well have had arms before it started interacting with NGC 1097, but it has lost its arms since then. Therefore it looks undisturbed.

Take a look at "The Eyes", NGC 4438 (which has arms) and NGC 4435 (which has not):

2019-05-07_5cd1d0208a20f_TheEyes_S1_HVLG_SS1040_CBS_HVLG_Curves_s[1].jpg

NGC 4438 and NGC 4435 are interacting. But only NGC 4438 looks disturbed,
because it has arms. NGC 4435 has not. Credit: KuriousGeorge.

Ann

Ok, thanks.

"It may very well have had arms before it started interacting with NGC 1097, but it has lost its arms since then. Therefore it looks undisturbed."

I also think that Ann is right here.
The fact that the two galaxies interact becomes quite obvious, especially in the IR.

Click to view full size image

biggg: https://live.staticflickr.com/65535/540 ... 6e69_o.jpg
Original data: NASA/ESA/CSA (GALEX/SST/JWST) jac berne (flickr)

[johnnydeep]

NGC 1097 and NGC 1097A. Credit: Mark Hanson.

---

NGC 1097 and NGC 1097A have much the same radial velocities, meaning that they are at much the same distance. They could indeed be entangled inside one another, but they will have their own velocity due to their interactions, which will suggest that they are at somewhat different distances. even though they are not.

The reason why NGC 1097 looks so undisturbed is almost certainly because it hasn't got any "arm fluff". It may very well have had arms before it started interacting with NGC 1097, but it has lost its arms since then. Therefore it looks undisturbed.

Take a look at "The Eyes", NGC 4438 (which has arms) and NGC 4435 (which has not):

2019-05-07_5cd1d0208a20f_TheEyes_S1_HVLG_SS1040_CBS_HVLG_Curves_s[1].jpg

NGC 4438 and NGC 4435 are interacting. But only NGC 4438 looks disturbed,
because it has arms. NGC 4435 has not. Credit: KuriousGeorge.

Ann

Ok, thanks.

"It may very well have had arms before it started interacting with NGC 1097, but it has lost its arms since then. Therefore it looks undisturbed."

I also think that Ann is right here.
The fact that the two galaxies interact becomes quite obvious, especially in the IR.

Click to view full size image

biggg: https://live.staticflickr.com/65535/540 ... 6e69_o.jpg
Original data: NASA/ESA/CSA (GALEX/SST/JWST) jac berne (flickr)

I don't see it. Why does this IR image show clear signs that the two galaxies are interacting that the optical image doesn't?

[Ann]

Ok, thanks.

"It may very well have had arms before it started interacting with NGC 1097, but it has lost its arms since then. Therefore it looks undisturbed."

I also think that Ann is right here.
The fact that the two galaxies interact becomes quite obvious, especially in the IR.

Click to view full size image

biggg: https://live.staticflickr.com/65535/540 ... 6e69_o.jpg
Original data: NASA/ESA/CSA (GALEX/SST/JWST) jac berne (flickr)

I don't see it. Why does this IR image show clear signs that the two galaxies are interacting that the optical image doesn't?

This is how you can tell that NGC 1097 and NGC 1097A are interacting:

NGC 1097 has two normal spiral arms. But it also has one patch of messy arm fluff surrounding satellite galaxy NGC 1097.

There would be no reason for an otherwise well-formed spiral galaxy like NGC 1097 to look so messy in that particular place if there wasn't a satellite galaxy there to mess things up. And indeed, we can see that there is a galaxy there, a small-looking galaxy.

We can either assume that this small-looking galaxy is a large background galaxy that has nothing to so with NGC 1097. The "arm chaos" and the presence of a galaxy seemingly located in the middle of that chaos is utter coincidence, in other words. Or else we conclude that the galaxy we see in the middle of the "arm mess" of NGC 1097 is indeed a small satellite galaxy whose presence is itself the cause of the chaotic shape of that spiral arm.

Almost all astronomers vote for the latter alternative.

Ann

[johnnydeep]

"It may very well have had arms before it started interacting with NGC 1097, but it has lost its arms since then. Therefore it looks undisturbed."

I also think that Ann is right here.
The fact that the two galaxies interact becomes quite obvious, especially in the IR.

Click to view full size image

biggg: https://live.staticflickr.com/65535/540 ... 6e69_o.jpg
Original data: NASA/ESA/CSA (GALEX/SST/JWST) jac berne (flickr)

I don't see it. Why does this IR image show clear signs that the two galaxies are interacting that the optical image doesn't?

This is how you can tell that NGC 1097 and NGC 1097A are interacting:


NGC 1097 NGC 1097A annotated Spitzer.png


NGC 1097 has two normal spiral arms. But it also has one patch of messy arm fluff surrounding satellite galaxy NGC 1097.

There would be no reason for an otherwise well-formed spiral galaxy like NGC 1097 to look so messy in that particular place if there wasn't a satellite galaxy there to mess things up. And indeed, we can see that there is a galaxy there, a small-looking galaxy.

We can either assume that this small-looking galaxy is a large background galaxy that has nothing to so with NGC 1097. The "arm chaos" and the presence of a galaxy seemingly located in the middle of that chaos is utter coincidence, in other words. Or else we conclude that the galaxy we see in the middle of the "arm mess" of NGC 1097 is indeed a small satellite galaxy whose presence is itself the cause of the chaotic shape of that spiral arm.

Almost all astronomers vote for the latter alternative.

Ann

You can also see most of that same disturbance in the optical image IMO. And I still think the mere appearance of a disturbance is not definitive. However, distance measurements and similar motion vectors (as you've already noted) could be. Good think I'm not an astronomer.

[AVAO]

I don't see it. Why does this IR image show clear signs that the two galaxies are interacting that the optical image doesn't?

This is how you can tell that NGC 1097 and NGC 1097A are interacting:


NGC 1097 NGC 1097A annotated Spitzer.png


NGC 1097 has two normal spiral arms. But it also has one patch of messy arm fluff surrounding satellite galaxy NGC 1097.

There would be no reason for an otherwise well-formed spiral galaxy like NGC 1097 to look so messy in that particular place if there wasn't a satellite galaxy there to mess things up. And indeed, we can see that there is a galaxy there, a small-looking galaxy.

We can either assume that this small-looking galaxy is a large background galaxy that has nothing to so with NGC 1097. The "arm chaos" and the presence of a galaxy seemingly located in the middle of that chaos is utter coincidence, in other words. Or else we conclude that the galaxy we see in the middle of the "arm mess" of NGC 1097 is indeed a small satellite galaxy whose presence is itself the cause of the chaotic shape of that spiral arm.

Almost all astronomers vote for the latter alternative.

Ann

You can also see most of that same disturbance in the optical image IMO. And I still think the mere appearance of a disturbance is not definitive. However, distance measurements and similar motion vectors (as you've already noted) could be. Good think I'm not an astronomer.

Thank you for the interesting question and discussion.

The galaxy is indeed very distorted, which in my opinion is not only due to the existence of NGC 1097A.

Click to view full size image 1 or image 2

I also looked at Hubble's zoom on NGC 1097A and have to admit that it does not allow any clear statement, except that NGC 1097A is an elliptical galaxy with a completely different morphology. If you compare this image with the star clusters of NGC 1097 in the immediate vicinity of NGC 1097A, there is a lot to suggest that NGC 1097A must be much further away. For a mini galaxy in the immediate vicinity, this would be a completely new type of galaxy, which seems unlikely. For the double-shelled halo phenomenon I have no explanation.

Click to view full size image

Original Data: NASA/ESA (HST) F555w jac berne (flickr)


...My personal favorites...

NGC 1097 in the WISE dust map:

Click to view full size image 1 or image 2

NGC 1097 core with JWST:

Click to view full size image

biggg: https://live.staticflickr.com/65535/540 ... d356_o.jpg
Original data: NASA/ESA/CSA JWST MIRI F770w

IC 169 (Legacy Surveys DR10)

Click to view full size image

NGC 681 (Legacy Surveys DR10)

Click to view full size image

ESO 199-012 (Legacy Surveys DR10)

Click to view full size image

[Ann]

Thank you for the interesting question and discussion.

The galaxy is indeed very distorted, which in my opinion is not only due to the existence of NGC 1097A.

Click to view full size image 1 or image 2

I also looked at Hubble's zoom on NGC 1097A and have to admit that it does not allow any clear statement, except that NGC 1097A is an elliptical galaxy with a completely different morphology. If you compare this image with the star clusters of NGC 1097 in the immediate vicinity of NGC 1097A, there is a lot to suggest that NGC 1097A must be much further away. For a mini galaxy in the immediate vicinity, this would be a completely new type of galaxy, which seems unlikely. For the double-shelled halo phenomenon I have no explanation.

Click to view full size image

Original Data: NASA/ESA (HST) F555w jac berne (flickr)


...My personal favorites...

NGC 1097 in the WISE dust map:

Click to view full size image 1 or image 2

NGC 1097 core with JWST:

Click to view full size image

biggg: https://live.staticflickr.com/65535/540 ... d356_o.jpg
Original data: NASA/ESA/CSA JWST MIRI F770w

Maybe, Jac, but you have not convinced me.

What we need to create a small galaxy shaped like NGC 1097A is a smallish barred galaxy that is interacting with a much larger bully of a galaxy until it loses its arms. We know for a fact that most smallish satellite galaxies interacting with large galaxies is that they are typically yellow, lacking in gas and non-starforming. The fact that the two largest satellites of the Milky Way, the Large and Small Magellanic Clouds, are so different, is clearly due to the fact that the Milky Way has only recently captured them.

NGC 1097 appears to have a broad stubby bar with no central core, which is indeed unusual. But there are certainly other smallish (but not dwarf) galaxies that have bars without a bright center. A very good example is the Large Magellanic Cloud. The LMC is not tiny, and most of its mass is probably concentrated in its bar.

The Large Magellanic Cloud. Credit: Primoz Cigler

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Large and massive-looking NGC 5996 has a relatively short and stubby bar which however contains a bright mass center. But its smaller companion, NGC 5994, appears to have a bar that contains no core.

Large barred spiral NGC 5996 and small barred spiral NGC 5994. Credit: ESA/Hubble & NASA, L. Galbany, J. Dalcanton, Dark Energy Survey/DOE/FNAL/DECam/CTIO/NOIRLab/NSF/AURA

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Another smallish (but not dwarf) galaxy that has a bar without a core is NGC 5068:

NGC 5068. Credit: NASA, ESA, R. Chandar (University of Toledo), and J. Lee (Space Telescope Science Institute); Processing: Gladys Kober (NASA/Catholic University of America)

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What I'm trying to say is that I don't think it's impossible for smallish galaxies to have substantial bars. I also think that small galaxies that interact with large massive galaxies for a long time are highly likely to lose their arms.

Ann