APOD: Arp 142: The Hummingbird Galaxy (2023 Sep 25)

[stacase@hotmail.com]

I probably never noticed before, but how can a Hubble photograph be copyrighted by an amateur astronomer?

Although it's not clear to me that the processor is claiming a copyright, he could (and in some countries there are certain automatic copyrights that occur). But this is not a "Hubble photograph". This is a derivative work created from Hubble data, and while the data itself is freely available to everyone, that does not mean that material produced from it is public domain.

Thanks

[johnnydeep]

Arp 142: The Hummingbird Galaxy

Explanation: What's happening to this spiral galaxy? Just a few hundred million years ago, NGC 2936, the upper of the two large galaxies shown at the bottom, was likely a normal spiral galaxy -- spinning, creating stars -- and minding its own business. But then it got too close to the massive elliptical galaxy NGC 2937, just below, and took a turn. Sometimes dubbed the Hummingbird Galaxy for its iconic shape, NGC 2936 is not only being deflected but also being distorted by the close gravitational interaction. Behind filaments of dark interstellar dust, bright blue stars form the nose of the hummingbird, while the center of the spiral appears as an eye. Alternatively, the galaxy pair, together known as Arp 142, look to some like Porpoise or a penguin protecting an egg. The featured re-processed image showing Arp 142 in great detail was taken recently by the Hubble Space Telescope. Arp 142 lies about 300 million light years away toward the constellation of the Water Snake (Hydra). In a billion years or so the two galaxies will likely merge into one larger galaxy.

The link-to the instagram post says something that makes no sense to me:

ARP 142 is not a single galaxy but rather a pair of interacting galaxies engaged in a cosmic dance. It consists of two main components: a smaller, irregular-shaped galaxy, and a larger, spiral-shaped galaxy. The smaller galaxy appears to be colliding with the larger one, triggering intense gravitational interactions.

So, yes, Arp 142 is the interacting galaxy pair consisting of the massive elliptical NGC 2937 below, and the massively distorted spiral NGC 2936 above it. So, what is the "smaller, irregular-shaped galaxy" if not NGC 2936? But the elliptical doesn't look "irregular" at all. And which one is smaller than the other by mass?

Also, is the smudge of stars that deceptively seems to be trailing upward from a foreground star (and looking quite like a comet!) yet another galaxy? If not, what is it?

And trying to summarize Ann's dialog with JohnD above, there are globular clusters visible in the foggy elliptical but no individual stars, whereas there ARE many massive big blue stars visible in the distorted elliptical. Yet both galaxies are much closer to each other than they are to us. Is that the upshot?

Click to view full size image

You got the picture right there, Johnny, because Arp 142 is NGC 2936 and NGC 4237! Arp 142 is the two of them!

(And yes: NGC 2936 and NGC 2937 are very very close to each other, much much closer to each other than they are to us.)

But there is only one elliptical galaxy in this APOD, not two. NGC 2936 is not an elliptical galaxy, but a distorted spiral. Elliptical galaxies are featureless, blob-shaped, dustlane-free, all-yellow bee swarms of stars orbiting a common center of mass. Just like NGC 2937.

The irregular galaxy is the "False Comet" in your picture. These galaxies are typically small, blue, devoid of a bright yellow center and devoid of any sort of regular shape or spiral arms.

The Small Magellanic Cloud is an irregular galaxy. Credit: NOIRLab/NSF/AURA

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I would guess that the irregular galaxy in the APOD is at the same distance as NGC 2936 and NGC 2937, because its stars are resolved to the same extent as the stars of NGC 2936.

However, using Simbad, I found that the designation of "the blue streak" in the APOD is LEDA 1237172. And actually, Simbad told me that LEDA 1237172 is not at the same distance as the two components as Arp 142, because their radial velocity is about 7,000 km/sec, whereas the radial velocity of LEDA 1237172 is "only" some 5,000 km/sec. That is probably a sufficiently significant difference to show that LEDA 1237172 is a foreground object.

Ann

So, again, the quoted text from the instagram page is just wrong:

ARP 142 is not a single galaxy but rather a pair of interacting galaxies engaged in a cosmic dance. It consists of two main components: a smaller, irregular-shaped galaxy, and a larger, spiral-shaped galaxy. The smaller galaxy appears to be colliding with the larger one, triggering intense gravitational interactions.

The pair of interacting galaxies comprises the compact elliptical plus the distorted spiral. The smaller irregular galaxy above them both is just photobombing and is not related (though at least one reference I've seen - and quoted by Pastorian in a post above - describes Arp 142 as a galaxy triple that includes it).

[Ann]

The link-to the instagram post says something that makes no sense to me:



So, yes, Arp 142 is the interacting galaxy pair consisting of the massive elliptical NGC 2937 below, and the massively distorted spiral NGC 2936 above it. So, what is the "smaller, irregular-shaped galaxy" if not NGC 2936? But the elliptical doesn't look "irregular" at all. And which one is smaller than the other by mass?

Also, is the smudge of stars that deceptively seems to be trailing upward from a foreground star (and looking quite like a comet!) yet another galaxy? If not, what is it?

And trying to summarize Ann's dialog with JohnD above, there are globular clusters visible in the foggy elliptical but no individual stars, whereas there ARE many massive big blue stars visible in the distorted elliptical. Yet both galaxies are much closer to each other than they are to us. Is that the upshot?

Click to view full size image

You got the picture right there, Johnny, because Arp 142 is NGC 2936 and NGC 4237! Arp 142 is the two of them!

(And yes: NGC 2936 and NGC 2937 are very very close to each other, much much closer to each other than they are to us.)

But there is only one elliptical galaxy in this APOD, not two. NGC 2936 is not an elliptical galaxy, but a distorted spiral. Elliptical galaxies are featureless, blob-shaped, dustlane-free, all-yellow bee swarms of stars orbiting a common center of mass. Just like NGC 2937.

The irregular galaxy is the "False Comet" in your picture. These galaxies are typically small, blue, devoid of a bright yellow center and devoid of any sort of regular shape or spiral arms.

The Small Magellanic Cloud is an irregular galaxy. Credit: NOIRLab/NSF/AURA

---

I would guess that the irregular galaxy in the APOD is at the same distance as NGC 2936 and NGC 2937, because its stars are resolved to the same extent as the stars of NGC 2936.

However, using Simbad, I found that the designation of "the blue streak" in the APOD is LEDA 1237172. And actually, Simbad told me that LEDA 1237172 is not at the same distance as the two components as Arp 142, because their radial velocity is about 7,000 km/sec, whereas the radial velocity of LEDA 1237172 is "only" some 5,000 km/sec. That is probably a sufficiently significant difference to show that LEDA 1237172 is a foreground object.

Ann

So, again, the quoted text from the instagram page is just wrong:

ARP 142 is not a single galaxy but rather a pair of interacting galaxies engaged in a cosmic dance. It consists of two main components: a smaller, irregular-shaped galaxy, and a larger, spiral-shaped galaxy. The smaller galaxy appears to be colliding with the larger one, triggering intense gravitational interactions.

The pair of interacting galaxies comprises the compact elliptical plus the distorted spiral. The smaller irregular galaxy above them both is just photobombing and is not related (though at least one reference I've seen - and quoted by Pastorian in a post above - describes Arp 142 as a galaxy triple that includes it).

Indeed, Johnny, the instagram text is wrong.

As for whether or not the irregular galaxy is sufficiently close to the Arp 142 pair to feel their gravity and be interacting with them, my initial guess was that it is close enough. I have no idea if it still possible that it might be at the same distance as NGC 2936 and NGC 2937, in spite of its different (but not wildly different) radial velocity.

Ann

[johnnydeep]

You got the picture right there, Johnny, because Arp 142 is NGC 2936 and NGC 4237! Arp 142 is the two of them!

(And yes: NGC 2936 and NGC 2937 are very very close to each other, much much closer to each other than they are to us.)

But there is only one elliptical galaxy in this APOD, not two. NGC 2936 is not an elliptical galaxy, but a distorted spiral. Elliptical galaxies are featureless, blob-shaped, dustlane-free, all-yellow bee swarms of stars orbiting a common center of mass. Just like NGC 2937.

The irregular galaxy is the "False Comet" in your picture. These galaxies are typically small, blue, devoid of a bright yellow center and devoid of any sort of regular shape or spiral arms.

The Small Magellanic Cloud is an irregular galaxy. Credit: NOIRLab/NSF/AURA

---

I would guess that the irregular galaxy in the APOD is at the same distance as NGC 2936 and NGC 2937, because its stars are resolved to the same extent as the stars of NGC 2936.

However, using Simbad, I found that the designation of "the blue streak" in the APOD is LEDA 1237172. And actually, Simbad told me that LEDA 1237172 is not at the same distance as the two components as Arp 142, because their radial velocity is about 7,000 km/sec, whereas the radial velocity of LEDA 1237172 is "only" some 5,000 km/sec. That is probably a sufficiently significant difference to show that LEDA 1237172 is a foreground object.

Ann

So, again, the quoted text from the instagram page is just wrong:

ARP 142 is not a single galaxy but rather a pair of interacting galaxies engaged in a cosmic dance. It consists of two main components: a smaller, irregular-shaped galaxy, and a larger, spiral-shaped galaxy. The smaller galaxy appears to be colliding with the larger one, triggering intense gravitational interactions.

The pair of interacting galaxies comprises the compact elliptical plus the distorted spiral. The smaller irregular galaxy above them both is just photobombing and is not related (though at least one reference I've seen - and quoted by Pastorian in a post above - describes Arp 142 as a galaxy triple that includes it).

Indeed, Johnny, the instagram text is wrong.

As for whether or not the irregular galaxy is sufficiently close to the Arp 142 pair to feel their gravity and be interacting with them, my initial guess was that it is close enough. I have no idea if it still possible that it might be at the same distance as NGC 2936 and NGC 2937, in spite of its different (but not wildly different) radial velocity.

Ann

Well, this site says they are quite far apart:

Above the pair, an unrelated, lone, bluish galaxy, inconsistently cataloged as UGC 5130, appears to be an elongated irregular or an edge-on spiral. Located 230 million light-years away, this galaxy is much closer to us than the colliding pair, and therefore is not interacting with them. It happens to lie along the same line of sight to foreground Milky Way stars caught in the image.

Arp 142 lies 326 million light-years away in the southern constellation Hydra. It is a member of the Arp catalog of peculiar galaxies observed by astronomer Halton C. Arp in the 1960s.

[AVAO]

Spiral galaxies aren't typically hugely symmetrical, although there are examples of galaxies that are. Like NGC 2857. But even in NGC 2857, there is more star formation in one arm than in the other:

NGC 2857. Credit: Sloan Digital Sky Survey.

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Other galaxies show a huge difference in the amount of star formation in their arms:

NGC 7496. Credit: ESA/Hubble & NASA, J. Lee and the PHANGS-HST Team Acknowledgement: J. Schmidt

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So we can't just assume that both arms of a spiral galaxy will contain the same (or more or less the same) amount of star formation.

As for the reddish color of much of NGC 2936, I still believe that these parts owe their color to dust, a myriad of small reddish stars - and, mind you, the sort of processing that made "the red parts" of the galaxy look extra red. I do believe that it would have been possible to process NGC 2936 so that its "red parts" looked less reddish.

However!! I do think that "the intrinsic color" of the non-blue parts of NGC 2936 is indeed redder than the intrinsic color of NGC 2937. The difference, I believe, is due to dust reddening. NGC 2936 contains a lot of dust, and its interaction with NGC 2937 may have scattered quite a bit of that dust across the disk of NGC 2936.

Take a look at nearby NGC 4038 and NGC 4039, the Antennae Galaxies, and note how dust is scattered across the disks of them and reddening their light, particularly their yellow populations.

---

So, Jac, I have just edited this post, and I took away the suggestion that NGC 2936 would originally have been similar to nearby spiral galaxy M81. M81 has a massive yellow bulge, and the bulge of NGC 2936 really doesn't look remarkably big at all.

One more thing, though. You wrote:

An explanation could be that the dust filaments in the rear part reflect the diffused galactic radiation over all, which does not happen in the front arm, so that the dust filaments appear brown and dark. Is there a better one?

I'm not sure what you mean by that. But bear in m ind that the combined light from galaxies is diffuse and faint. So if you start out with diffuse, faint and scattered light, you are not going to get any sort of bright reflection nebulosity out of that.

There really is dust in the Milky Way that reflects the combined light of our galaxy. The nebulosity it creates is called the Integrated Flux Nebula, or IFN. You can see it in this great picture of Polaris and cluster NGC 188:

The Integrated Flux Nebula surrounding Polaris and NGC 188. Credit: Kush.Chandaria

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But the Integrated Flux Nebula is typically quite faint. I doubt that it would affect the overall appearance of a galaxy.

As to what NGC 2936 originally would have looked like, I don't know. And as to what it would look like if we could see it from another perspective, I frankly have no idea!

Ann

ThanX Ann

...for all your interesting explanations. I think there are still some secrets to be revealed about Arp 142.
Even when it comes to who interacts with whom and how .-)

Click to view full size image

bigg: https://live.staticflickr.com/65535/532 ... 893b_o.jpg
jac berne (flickr)

[johnnydeep]

...
ThanX Ann

...for all your interesting explanations. I think there are still some secrets to be revealed about Arp 142.
Even when it comes to who interacts with whom and how .-)

Click to view full size image

bigg: https://live.staticflickr.com/65535/532 ... 893b_o.jpg
jac berne (flickr)

What are you hinting at here? That one or more of those small reddish seemingly distant background galaxies are interacting with NGC 2936? I don't see any clear sign of that at all, superficial appearances to the contrary notwithstanding.

[AVAO]

...
ThanX Ann

...for all your interesting explanations. I think there are still some secrets to be revealed about Arp 142.
Even when it comes to who interacts with whom and how .-)

Click to view full size image

bigg: https://live.staticflickr.com/65535/532 ... 893b_o.jpg
jac berne (flickr)

What are you hinting at here? That one or more of those small reddish seemingly distant background galaxies are interacting with LEDA 1237172 / UGC 5130? I don't see any clear sign of that at all, superficial appearances to the contrary notwithstanding.

Well. The suggestion was intended as a stimulus for discussion. Halton Arp, who also studied this group of galaxies, was also a convinced advocate of his theory that, at least in the case of quasars, the redshift is not (only) a feature of distance but (also) of age. However, as far as I know, he did not dare to extend this generally to redshifted background galaxies, which would then have implied a model of "baby galaxies"... The fact that in JWST even strongly redshifted background galaxies are already strongly structured is likely to contribute to this discussion again give a new wind.

I myself have analysed the phenomenon of seemingly interacting background galaxies in more detail in many other examples and have not been able to find any convincing evidence that would conclusively support this hypothesis. That's why I dropped this one again.

The same thing could also be discussed between galaxies and the flux nebula mentioned by Ann or the submillimeter range (which correlates strongly with the flux nebula structures). But even there, the question between accidental coincidence of structures and real interaction has so far remained without conclusive evidence in my research.

What's interesting about the example above, "the apparently nested baby galaxy" - I'll call it that now anyway - is the difference between the left and right sides. On the right, the dust clouds from NGC 2936 become visible, but on the left, the bright star and gas clouds appear to be additionally brightened. Which brings us back to my previous discussion with Ann.

But back to your question: I also do not see any clear sign of that at all, superficial appearances to the contrary notwithstanding.

[Ann]

...
ThanX Ann

...for all your interesting explanations. I think there are still some secrets to be revealed about Arp 142.
Even when it comes to who interacts with whom and how .-)

Click to view full size image

bigg: https://live.staticflickr.com/65535/532 ... 893b_o.jpg
jac berne (flickr)

What are you hinting at here? That one or more of those small reddish seemingly distant background galaxies are interacting with LEDA 1237172 / UGC 5130? I don't see any clear sign of that at all, superficial appearances to the contrary notwithstanding.

Well. The suggestion was intended as a stimulus for discussion. Halton Arp, who also studied this group of galaxies, was also a convinced advocate of his theory that, at least in the case of quasars, the redshift is not (only) a feature of distance but (also) of age. However, as far as I know, he did not dare to extend this generally to redshifted background galaxies, which would then have implied a model of "baby galaxies"... The fact that in JWST even strongly redshifted background galaxies are already strongly structured is likely to contribute to this discussion again give a new wind.

I myself have analysed the phenomenon of seemingly interacting background galaxies in more detail in many other examples and have not been able to find any convincing evidence that would conclusively support this hypothesis. That's why I dropped this one again.

The same thing could also be discussed between galaxies and the flux nebula mentioned by Ann or the submillimeter range (which correlates strongly with the flux nebula structures). But even there, the question between accidental coincidence of structures and real interaction has so far remained without conclusive evidence in my research.

What's interesting about the example above, "the apparently nested baby galaxy" - I'll call it that now anyway - is the difference between the left and right sides. On the right, the dust clouds from NGC 2936 become visible, but on the left, the bright star and gas clouds appear to be additionally brightened. Which brings us back to my previous discussion with Ann.

But back to your question: I also do not see any clear sign of that at all, superficial appearances to the contrary notwithstanding.

You lost me there, Jac. The background galaxies that can be seen behind NGC 2936 are not that far behind. They don't hark back to the beginning of time. We have no reason to think of them as "baby galaxies", the way we think of the first galaxies in the Universe.

If there is another hypothesis about baby galaxies, I haven't heard of it.

I don't find the difference between the background galaxies on the right and on the left side of the distorted spiral arm of NGC 2936 remarkable. Background galaxies look different for two reasons, 1) because of the amount of dust in front of them when they are seen through the disk or through the arm of a galaxy, for example), and 2) because of the intrinsic qualities of the background galaxies themselves. A background galaxy that is bursting with hot ultraviolet stars is going to look decidedly different than a galaxy at the same distance that is dominated by cool infrared stars.

So I don't find the difference in appearance of the background galaxies remarkable.

What I do find strange, the more I think about it, is the very red appearance of NGC 2936 compared to NGC 2937 (and perhaps compared to the background galaxies as well).

NGC 2937 at left and NGC 2936 at right. Image credit: NASA, ESA, Hubble, HLA; Processing & Copyright: Basudeb Chakrabarti

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NGC 2937 at left and NGC 2936 at right. Image credit: Sloan Digital Sky Survey

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Compare the APOD with the (very small) picture from Sloan Digital Sky Survey (SDSS). I trust SDSS, because I find their colors consistent. Note how the colors of NGC 2936 and NGC 2937 are wildly different in the APOD - NGC 2937 is almost white, whereas NGC 2937 is strikingly reddish.

But the SDSS image does not look like that at all. We can see that the core of NGC 2936 is reddened by a dust lane in front of it, but other than that, the colors of NGC 2936 and NGC 2937 are mostly the same. Apart from the blue stars in NGC 2936 and the obvious dust lanes in it, the two galaxies are, more or less, the same yellow color.

I think that is correct, because the yellow color in both galaxies comes from the same type of stars. Trying to explain the reddish color of NGC 2936 in the APOD is therefore futile.

Ann

[AVAO]

Well. The suggestion was intended as a stimulus for discussion. Halton Arp, who also studied this group of galaxies, was also a convinced advocate of his theory that, at least in the case of quasars, the redshift is not (only) a feature of distance but (also) of age. However, as far as I know, he did not dare to extend this generally to redshifted background galaxies, which would then have implied a model of "baby galaxies"... The fact that in JWST even strongly redshifted background galaxies are already strongly structured is likely to contribute to this discussion again give a new wind.

I myself have analysed the phenomenon of seemingly interacting background galaxies in more detail in many other examples and have not been able to find any convincing evidence that would conclusively support this hypothesis. That's why I dropped this one again.
...

You lost me there, Jac. The background galaxies that can be seen behind NGC 2936 are not that far behind. They don't hark back to the beginning of time. We have no reason to think of them as "baby galaxies", the way we think of the first galaxies in the Universe.
...

I don't disagree with that in any way. Personally, I find Halton Arp's idea regarding the life cycle of quasars "interesting", but I don't believe in extending this to normal galaxies or generally questioning the redshift as a means of measuring distances.

Jac

[johnnydeep]

Well. The suggestion was intended as a stimulus for discussion. Halton Arp, who also studied this group of galaxies, was also a convinced advocate of his theory that, at least in the case of quasars, the redshift is not (only) a feature of distance but (also) of age. However, as far as I know, he did not dare to extend this generally to redshifted background galaxies, which would then have implied a model of "baby galaxies"... The fact that in JWST even strongly redshifted background galaxies are already strongly structured is likely to contribute to this discussion again give a new wind.

I myself have analysed the phenomenon of seemingly interacting background galaxies in more detail in many other examples and have not been able to find any convincing evidence that would conclusively support this hypothesis. That's why I dropped this one again.
...

You lost me there, Jac. The background galaxies that can be seen behind NGC 2936 are not that far behind. They don't hark back to the beginning of time. We have no reason to think of them as "baby galaxies", the way we think of the first galaxies in the Universe.
...

I don't disagree with that in any way. Personally, I find Halton Arp's idea regarding the life cycle of quasars "interesting", but I don't believe in extending this to normal galaxies or generally questioning the redshift as a means of measuring distances.

Jac

{ Note: my reply above mistakenly mentioned the blue galaxy at the top of the APOD as the one (not) interacting with the small red background galaxies from AVAO's post, which I've since corrected. Of course those are near NGC 2936, not the upper blue galaxy which they are nowhere near. My bad. ]

Now, about "questioning redshift as a distance measure", what do you guys think of that paper that came out a few months ago that was espousing the "tired light" theory (among other questionable things) and that came to the conclusion that the universe was almost twice as old as standard cosmology predicts? Although it made for eyebrow raising click-bait, the paper was quickly taken to task by others (here for example - https://www.astronomy.com/science/is-th ... e-thought/).

[PoorChoiceOfWords]

Does anybody else see a cat in this image? The cat I see is at the bottom of NGC 2936. It's a striped cat with the stripes going vertically. The cat's tail is straight up with a curl at the end, the right back leg is forward while the left back leg is back and both front legs are together with its head up...

[johnnydeep]

Does anybody else see a cat in this image? The cat I see is at the bottom of NGC 2936. It's a striped cat with the stripes going vertically. The cat's tail is straight up with a curl at the end, the right back leg is forward while the left back leg is back and both front legs are together with its head up...

Well, now that you've described it, I do see it (though the head is less clearly defined than the body):

[Ann]

Does anybody else see a cat in this image? The cat I see is at the bottom of NGC 2936. It's a striped cat with the stripes going vertically. The cat's tail is straight up with a curl at the end, the right back leg is forward while the left back leg is back and both front legs are together with its head up...

Well, now that you've described it, I do see it (though the head is less clearly defined than the body):

Click to view full size image

Thanks for showing it to us, Johnny! I absolutely couldn't see it, but it makes me happy to see cats!

Click to view full size image

Oh, and - if the entire galaxy is a Hummingbird Nebula, then I can't help thinking that the kitty in the nebula must be licking its lips!

Ann

[johnnydeep]

Does anybody else see a cat in this image? The cat I see is at the bottom of NGC 2936. It's a striped cat with the stripes going vertically. The cat's tail is straight up with a curl at the end, the right back leg is forward while the left back leg is back and both front legs are together with its head up...

Well, now that you've described it, I do see it (though the head is less clearly defined than the body):

Click to view full size image

Thanks for showing it to us, Johnny! I absolutely couldn't see it, but it makes me happy to see cats!

Click to view full size image

Oh, and - if the entire galaxy is a Hummingbird Nebula, then I can't help thinking that the kitty in the nebula must be licking its lips!

Ann

In which case, the cat's appetite is far too big for its body!