APOD: Unusual Spiral Galaxy M66 from Webb (2023 Aug 29)

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APOD: Unusual Spiral Galaxy M66 from Webb (2023 Aug 29)

Post by APOD Robot » Tue Aug 29, 2023 4:08 am

Image Unusual Spiral Galaxy M66 from Webb

Explanation: Why isn't spiral galaxy M66 symmetric? Usually, density waves of gas, dust, and newly formed stars circle a spiral galaxy's center and create a nearly symmetric galaxy. The differences between M66's spiral arms and the apparent displacement of its nucleus are all likely caused by previous close interactions and the tidal gravitational pulls of nearby galaxy neighbors M65 and NGC 3628. The galaxy, featured here in infrared light taken by the James Webb Space Telescope, spans about 100,000 light years, lies about 35 million light years distant, and is the largest galaxy in a group known as the Leo Triplet. Like many spiral galaxies, the long and intricate dust lanes of M66 are seen intertwined with the bright stars and intergalactic dust that follow the spiral arms.

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Re: APOD: Unusual Spiral Galaxy M66 from Webb (2023 Aug 29)

Post by Ann » Tue Aug 29, 2023 6:09 am


I found another version of the JWST portrait of M66, processed by another person. And as long as everything we see is infrared light, we can map it to whatever visible colors we want to, right?

The dust that is highlighted by the JWST image is the raw material for star formation in M66. The dust is also the "stabilizer" for the spiral shape of M66 in the first place. It is possible to find "fossil" all-yellow apparently dust-free galaxies with a weak spiral structure, but the way I understand it, well-ordered "spiral dust structures" is what "upholds the spiral-ness of spiral galaxies".

Anyway, the Leo Triplet. I found a picture that I really liked, but it is an AAPOD2 image, and I'm not absolutely sure it is safe to open links to them. Is it, bystander? Well, I uploaded the image to my computer, and here it is, perfectly harmless:

Leo Triplet AAPOD2 Boris Vladimirovich.png
Leo Triplet. Credit: Boris Vladimirovich

In Boris Vladimirovich's image, M66 is at top left, M65 is at bottom and NGC 3628 is at top right. I'm not sure that M66 is the largest of the galaxies in the Leo Triplet, because NGC 3628 looks bigger to me.

Note that the dust lanes of M66 are red from hydrogen alpha in Boris Vladimirovich's image, and we can also see a few young blue star clusters. There is certainly star formation going on in this galaxy. If you want some technical information on how Boris Vladimirovich acquired his image, it is here (the AAPOD2 link).

By contrast, the other two galaxies of the Leo Triplet lack red nebulas and obvious blue star clusters.

NGC 3628 has a fantastic long tail:


Interestingly, NGC 3628 is very slightly similar to those jellyfish galaxies that fall through the intergalactic medium of a large galaxy cluster and are compressed on one side and lose their gas on the other side:


Interestingly, NGC 3628 seems to be flying away from the other two galaxies, And that is indeed possible: It may have received a "tidal kick" that made it fly away in this direction. But it is sure to come back!

Because the galaxies of the Leo Triplet are indeed interacting. That is why NGC 3628 looks so squished and puffed up at the same time, and that is why M66 is somewhat asymmetrically shaped and why it is forming quite a lot of stars. And that may just possibly be why sedate M65, that looks fit for an old galaxies' retirement home, suddenly blew a core collapse supernova back in 2013. 💥


The world, and certainly the Universe, is full of surprises!

Ann
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Re: APOD: Unusual Spiral Galaxy M66 from Webb (2023 Aug 29)

Post by michaelgriffith » Tue Aug 29, 2023 6:36 am

I found another version of the JWST portrait of M66, processed by another person. And as long as everything we see is infrared light, we can map it to whatever visible colors we want toangry gran, right?

The dust that is highlighted by the JWST image is the raw material for star formation in M66. The dust is also the "stabilizer" for the spiral shape of M66 in the first place. It is possible to find "fossil" all-yellow apparently dust-free galaxies with a weak spiral structure, but the way I understand it, well-ordered "spiral dust structures" is what "upholds the spiral-ness of spiral galaxies".
I'm so surprised with information of Ann, especially the JWST image. The structure of dust seems more magical than my thought.

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Re: APOD: Unusual Spiral Galaxy M66 from Webb (2023 Aug 29)

Post by AVAO » Tue Aug 29, 2023 4:51 pm

Ann wrote: Tue Aug 29, 2023 6:09 am ...
I found another version of the JWST portrait of M66, processed by another person. And as long as everything we see is infrared light, we can map it to whatever visible colors we want to, right?
...
Ann
ThanX Ann

I like this version of "Go Webb! (Unofficial)".
Filters: F770W Blue; F1000W Cyan; F1130W Yellow; F2100W Red (slightly color temp adjusted overall)
But well, depending on which filters are transferred to RGB, the result is different again.
big:https://live.staticflickr.com/65535/526 ... 24a_o.png

However, I can find few images on the net that use the "official" JWST filter assignment. This would enable better scientific comparability. But depending on that, spatiality and depth are then lost.
Image
https://jwst-docs.stsci.edu/jwst-mid-in ... ingfilters

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Re: APOD: Unusual Spiral Galaxy M66 from Webb (2023 Aug 29)

Post by johnnydeep » Tue Aug 29, 2023 7:21 pm

Why does this mention a "displaced nucleus"? I see one nucleus in what I would call the exact center, and a thoroughly disrupted spiral arm. Or is the reference to a possible second nucleus at about the 4:30 position? To me that just looks like an unusually dense knot of stars in the spiral arm.
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Re: APOD: Unusual Spiral Galaxy M66 from Webb (2023 Aug 29)

Post by Chris Peterson » Tue Aug 29, 2023 7:59 pm

johnnydeep wrote: Tue Aug 29, 2023 7:21 pm Why does this mention a "displaced nucleus"? I see one nucleus in what I would call the exact center, and a thoroughly disrupted spiral arm. Or is the reference to a possible second nucleus at about the 4:30 position? To me that just looks like an unusually dense knot of stars in the spiral arm.
To my eyes, the nucleus is much closer to the end of the upper arm than the lower one. If I saw this image with no nucleus and was asked to suggest where it should be, I'd place it lower.
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Re: APOD: Unusual Spiral Galaxy M66 from Webb (2023 Aug 29)

Post by johnnydeep » Tue Aug 29, 2023 8:20 pm

Chris Peterson wrote: Tue Aug 29, 2023 7:59 pm
johnnydeep wrote: Tue Aug 29, 2023 7:21 pm Why does this mention a "displaced nucleus"? I see one nucleus in what I would call the exact center, and a thoroughly disrupted spiral arm. Or is the reference to a possible second nucleus at about the 4:30 position? To me that just looks like an unusually dense knot of stars in the spiral arm.
To my eyes, the nucleus is much closer to the end of the upper arm than the lower one. If I saw this image with no nucleus and was asked to suggest where it should be, I'd place it lower.
I'm not clear on where the inner "end" of either arm is, but if the quite clearly seen nucleus is closer to one arm's end than the other, that would just reflect a disrupted spiral arm (or two). Meaning that it's the arm that's displaced, not the nucleus!
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Re: APOD: Unusual Spiral Galaxy M66 from Webb (2023 Aug 29)

Post by Chris Peterson » Tue Aug 29, 2023 8:24 pm

johnnydeep wrote: Tue Aug 29, 2023 8:20 pm
Chris Peterson wrote: Tue Aug 29, 2023 7:59 pm
johnnydeep wrote: Tue Aug 29, 2023 7:21 pm Why does this mention a "displaced nucleus"? I see one nucleus in what I would call the exact center, and a thoroughly disrupted spiral arm. Or is the reference to a possible second nucleus at about the 4:30 position? To me that just looks like an unusually dense knot of stars in the spiral arm.
To my eyes, the nucleus is much closer to the end of the upper arm than the lower one. If I saw this image with no nucleus and was asked to suggest where it should be, I'd place it lower.
I'm not clear on where the inner "end" of either arm is, but if the quite clearly seen nucleus is closer to one arm's end than the other, that would just reflect a disrupted spiral arm (or two). Meaning that it's the arm that's displaced, not the nucleus!
It's all relative. It's a displacement between the arms and the nucleus. Visually, it is seen as the nucleus being off center, so I think the wording is reasonable.
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Re: APOD: Unusual Spiral Galaxy M66 from Webb (2023 Aug 29)

Post by johnnydeep » Tue Aug 29, 2023 8:34 pm

Chris Peterson wrote: Tue Aug 29, 2023 8:24 pm
johnnydeep wrote: Tue Aug 29, 2023 8:20 pm
Chris Peterson wrote: Tue Aug 29, 2023 7:59 pm

To my eyes, the nucleus is much closer to the end of the upper arm than the lower one. If I saw this image with no nucleus and was asked to suggest where it should be, I'd place it lower.
I'm not clear on where the inner "end" of either arm is, but if the quite clearly seen nucleus is closer to one arm's end than the other, that would just reflect a disrupted spiral arm (or two). Meaning that it's the arm that's displaced, not the nucleus!
It's all relative. It's a displacement between the arms and the nucleus. Visually, it is seen as the nucleus being off center, so I think the wording is reasonable.
Alright. But it's not the clearest wording IMHO. I guess it's making a distinction between galaxies with spiral arms that are disrupted only far away from the nucleus and galaxies whose spiral arm disruption extends all the way to the nucleus.
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Re: APOD: Unusual Spiral Galaxy M66 from Webb (2023 Aug 29)

Post by orin stepanek » Tue Aug 29, 2023 10:03 pm

M66_JwstTomlinson_1080.jpg
In my mind the galaxy doesn't look unusual at all; and I think it is
very beautiful! Seeing it how it look is in the eye of the beholder! :wink:
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Re: APOD: Unusual Spiral Galaxy M66 from Webb (2023 Aug 29)

Post by musigeek » Wed Aug 30, 2023 12:52 am

I looked at this picture and thought "That looks pretty grainy. Waitaminute! Are those stars? Can JWST actually resolve individual stars at that distance?

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Re: APOD: Unusual Spiral Galaxy M66 from Webb (2023 Aug 29)

Post by Chris Peterson » Wed Aug 30, 2023 12:55 am

musigeek wrote: Wed Aug 30, 2023 12:52 am I looked at this picture and thought "That looks pretty grainy. Waitaminute! Are those stars? Can JWST actually resolve individual stars at that distance?
Yes and no. It can certainly resolve them in the sense of isolating individual stars against the background. So can Hubble. So can backyard astroimagers on Earth. It can often isolate more of them given its nature, but that's the main difference.

I think most of the graininess you're seeing here is, in fact, noise. Not stars.
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Re: APOD: Unusual Spiral Galaxy M66 from Webb (2023 Aug 29)

Post by Ann » Wed Aug 30, 2023 4:46 am

musigeek wrote: Wed Aug 30, 2023 12:52 am I looked at this picture and thought "That looks pretty grainy. Waitaminute! Are those stars? Can JWST actually resolve individual stars at that distance?

Some of them are stars, or else they are some low-temperature byproducts of stars in the vicinity:

APOD 29 August 2023 annotated.png

You can see a number of distinct red blips at certain places in the JWST of M66. These are either stars, or else they are low-temperature byproducts of stars in the vicinity of the stars.

I'd say they are most likely stars. Take a look at a Hubble picture of almost the same region of M66:

M66 annotated ESA Hubble NASA.png
M66. Credit: NASA, ESA, Hubble, Janice Lee, Leo Shatz

Note the "blue cloud of stars" to the lower left of the core of M66 in the Hubble picture. This blue cloud corresponds exactly to the position of the "red blips" to the left of the core in the JWST photo.

But wait, you say. Surely JWST can't see blue stars? No, it can't. But in a region where there are a lot of hot bright blue stars, there are almost always a few large cool red supergiants, too. These large bright very cool supergiant stars is what JWST is seeing.


The Double Cluster of Perseus are dominated by massive stars that are hot, bright and blue. But there are some very cool, bright red supergiants among the blue stars.


Alternatively, if the red blips in the JWST image are not stars, they might be free-floating clouds of gas and dust like this fascinating caterpillar in the Carina Nebula:


On the other hand, I expect these Bok globules to exist mostly in regions of active star formation where there are large clouds that the small Bok globules to break off of. And the red blips in the JWST image are mostly seen where there isn't a lot of dust. Which, again, suggests that these things are stars.

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Re: APOD: Unusual Spiral Galaxy M66 from Webb (2023 Aug 29)

Post by johnnydeep » Wed Aug 30, 2023 12:51 pm

Chris Peterson wrote: Wed Aug 30, 2023 12:55 am
musigeek wrote: Wed Aug 30, 2023 12:52 am I looked at this picture and thought "That looks pretty grainy. Waitaminute! Are those stars? Can JWST actually resolve individual stars at that distance?
Yes and no. It can certainly resolve them in the sense of isolating individual stars against the background. So can Hubble. So can backyard astroimagers on Earth. It can often isolate more of them given its nature, but that's the main difference.

I think most of the graininess you're seeing here is, in fact, noise. Not stars.
How is it proven that it's actually individual stars that are being "isolated" against the background in images of galaxies millions of lightyears away, and not noise or perhaps small clusters of stars?
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Re: APOD: Unusual Spiral Galaxy M66 from Webb (2023 Aug 29)

Post by Chris Peterson » Wed Aug 30, 2023 1:39 pm

johnnydeep wrote: Wed Aug 30, 2023 12:51 pm
Chris Peterson wrote: Wed Aug 30, 2023 12:55 am
musigeek wrote: Wed Aug 30, 2023 12:52 am I looked at this picture and thought "That looks pretty grainy. Waitaminute! Are those stars? Can JWST actually resolve individual stars at that distance?
Yes and no. It can certainly resolve them in the sense of isolating individual stars against the background. So can Hubble. So can backyard astroimagers on Earth. It can often isolate more of them given its nature, but that's the main difference.

I think most of the graininess you're seeing here is, in fact, noise. Not stars.
How is it proven that it's actually individual stars that are being "isolated" against the background in images of galaxies millions of lightyears away, and not noise or perhaps small clusters of stars?
Not noise because it's repeatable. A star makes a different shape on a sensor than a cluster, and individual stars are spectroscopically different from groups of them. And, of course, many stars are variable, and that can be measured. Cepheids are the obvious case. I can see and measure those from my observatory with a 10" telescope!
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Re: APOD: Unusual Spiral Galaxy M66 from Webb (2023 Aug 29)

Post by AVAO » Wed Aug 30, 2023 3:17 pm

musigeek wrote: Wed Aug 30, 2023 12:52 am I looked at this picture and thought "That looks pretty grainy. Waitaminute! Are those stars? Can JWST actually resolve individual stars at that distance?
Today's APOD shows various JWST filters overlaid. If you only want to see the stars separately, it is advantageous to study filters close to the optical spectrum such as the F200W filter below. The resolution never fails to amaze me. You have the feeling of being able to count each star individually, even if the star density increases so much towards the center that no individual stars remain separately recognizable in the central area.

M66 (NGC 3627) cutout https://live.staticflickr.com/65535/531 ... 791f_k.jpg[/url] 5 seconds to wait
Original Data Source: NASA / ESA / CSA (JWST) jac berne (flickr)
Last edited by AVAO on Thu Aug 31, 2023 4:02 am, edited 1 time in total.

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Re: APOD: Unusual Spiral Galaxy M66 from Webb (2023 Aug 29)

Post by johnnydeep » Wed Aug 30, 2023 7:19 pm

Chris Peterson wrote: Wed Aug 30, 2023 1:39 pm
johnnydeep wrote: Wed Aug 30, 2023 12:51 pm
Chris Peterson wrote: Wed Aug 30, 2023 12:55 am

Yes and no. It can certainly resolve them in the sense of isolating individual stars against the background. So can Hubble. So can backyard astroimagers on Earth. It can often isolate more of them given its nature, but that's the main difference.

I think most of the graininess you're seeing here is, in fact, noise. Not stars.
How is it proven that it's actually individual stars that are being "isolated" against the background in images of galaxies millions of lightyears away, and not noise or perhaps small clusters of stars?
Not noise because it's repeatable. A star makes a different shape on a sensor than a cluster, and individual stars are spectroscopically different from groups of them. And, of course, many stars are variable, and that can be measured. Cepheids are the obvious case. I can see and measure those from my observatory with a 10" telescope!
By "different shape" what do you mean? Stars are point sources. Wouldn't a dense enough cluster also be a point source provided it was far enough away? And how about multiple star systems. They're point sources too I presume, but their members can still be distinguished spectroscopically, right? As for variable stars, if one was a member of a small cluster, we'd still notice the variability.
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Re: APOD: Unusual Spiral Galaxy M66 from Webb (2023 Aug 29)

Post by Chris Peterson » Wed Aug 30, 2023 7:24 pm

johnnydeep wrote: Wed Aug 30, 2023 7:19 pm
Chris Peterson wrote: Wed Aug 30, 2023 1:39 pm
johnnydeep wrote: Wed Aug 30, 2023 12:51 pm

How is it proven that it's actually individual stars that are being "isolated" against the background in images of galaxies millions of lightyears away, and not noise or perhaps small clusters of stars?
Not noise because it's repeatable. A star makes a different shape on a sensor than a cluster, and individual stars are spectroscopically different from groups of them. And, of course, many stars are variable, and that can be measured. Cepheids are the obvious case. I can see and measure those from my observatory with a 10" telescope!
By "different shape" what do you mean? Stars are point sources. Wouldn't a dense enough cluster also be a point source provided it was far enough away? And how about multiple star systems. They're point sources too I presume, but their members can still be distinguished spectroscopically, right? As for variable stars, if one was a member of a small cluster, we'd still notice the variability.
A cluster of stars would have to be awfully far away to look like a point source. Farther than any of these relatively nearby galaxies that we're looking at. It's likely that we couldn't distinguish a single star from a multiple star system, unless we viewed the system edge on and could detect eclipsing. Or, as you suggest, by some spectroscopic features, depending on the stellar types involved.
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Re: APOD: Unusual Spiral Galaxy M66 from Webb (2023 Aug 29)

Post by johnnydeep » Wed Aug 30, 2023 7:26 pm

AVAO wrote: Wed Aug 30, 2023 3:17 pm
musigeek wrote: Wed Aug 30, 2023 12:52 am I looked at this picture and thought "That looks pretty grainy. Waitaminute! Are those stars? Can JWST actually resolve individual stars at that distance?
Today's APOD shows various JWST filters overlaid. If you only want to see the stars separately, it is advantageous to study filters close to the optical spectrum such as the F200W filter below. The resolution never fails to amaze me. You have the feeling of being able to count each star individually, even if the star density increases so much towards the center that no individual stars remain separately recognizable in the central area.

M66 (NGC 3627) cutout biggg: https://live.staticflickr.com/65535/531 ... 6707_o.jpg 5 seconds to wait
Original Data Source: NASA / ESA / CSA (JWST) jac berne (flickr)
Yes, that's very impressive. And the color inverted version is even more so! Here's a zoom-in on those two knots of stars in the lower arm:

m66 high res inverted zoom in to knots.jpg
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Re: APOD: Unusual Spiral Galaxy M66 from Webb (2023 Aug 29)

Post by Ann » Wed Aug 30, 2023 8:16 pm

johnnydeep wrote: Wed Aug 30, 2023 7:26 pm
AVAO wrote: Wed Aug 30, 2023 3:17 pm
musigeek wrote: Wed Aug 30, 2023 12:52 am I looked at this picture and thought "That looks pretty grainy. Waitaminute! Are those stars? Can JWST actually resolve individual stars at that distance?
Today's APOD shows various JWST filters overlaid. If you only want to see the stars separately, it is advantageous to study filters close to the optical spectrum such as the F200W filter below. The resolution never fails to amaze me. You have the feeling of being able to count each star individually, even if the star density increases so much towards the center that no individual stars remain separately recognizable in the central area.

M66 (NGC 3627) cutout biggg: https://live.staticflickr.com/65535/531 ... 6707_o.jpg 5 seconds to wait
Original Data Source: NASA / ESA / CSA (JWST) jac berne (flickr)
Yes, that's very impressive. And the color inverted version is even more so! Here's a zoom-in on those two knots of stars in the lower arm:

That's impressive indeed!

Speaking of impressive, though unfortunately off topic, I just found a fantastic JWST picture of NGC 1566. I'm almost certain that this picture has been posted somewhere here at Starship Asterisk* before - maybe even as an APOD? - but I find the image so gorgeous that I can't resist posting it again:


A larger version of the picture is here. Anyway, talk about NGC 1566 being a picture-perfect spiral galaxy!!

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Re: APOD: Unusual Spiral Galaxy M66 from Webb (2023 Aug 29)

Post by johnnydeep » Wed Aug 30, 2023 8:42 pm

Chris Peterson wrote: Wed Aug 30, 2023 7:24 pm
johnnydeep wrote: Wed Aug 30, 2023 7:19 pm
Chris Peterson wrote: Wed Aug 30, 2023 1:39 pm
Not noise because it's repeatable. A star makes a different shape on a sensor than a cluster, and individual stars are spectroscopically different from groups of them. And, of course, many stars are variable, and that can be measured. Cepheids are the obvious case. I can see and measure those from my observatory with a 10" telescope!
By "different shape" what do you mean? Stars are point sources. Wouldn't a dense enough cluster also be a point source provided it was far enough away? And how about multiple star systems. They're point sources too I presume, but their members can still be distinguished spectroscopically, right? As for variable stars, if one was a member of a small cluster, we'd still notice the variability.
A cluster of stars would have to be awfully far away to look like a point source. Farther than any of these relatively nearby galaxies that we're looking at. It's likely that we couldn't distinguish a single star from a multiple star system, unless we viewed the system edge on and could detect eclipsing. Or, as you suggest, by some spectroscopic features, depending on the stellar types involved.
How far? What's the minimum angular separation needed to cover more than 1 pixel in a CCD? Or is that the wrong measurement?
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Re: APOD: Unusual Spiral Galaxy M66 from Webb (2023 Aug 29)

Post by Chris Peterson » Wed Aug 30, 2023 9:01 pm

johnnydeep wrote: Wed Aug 30, 2023 8:42 pm
Chris Peterson wrote: Wed Aug 30, 2023 7:24 pm
johnnydeep wrote: Wed Aug 30, 2023 7:19 pm

By "different shape" what do you mean? Stars are point sources. Wouldn't a dense enough cluster also be a point source provided it was far enough away? And how about multiple star systems. They're point sources too I presume, but their members can still be distinguished spectroscopically, right? As for variable stars, if one was a member of a small cluster, we'd still notice the variability.
A cluster of stars would have to be awfully far away to look like a point source. Farther than any of these relatively nearby galaxies that we're looking at. It's likely that we couldn't distinguish a single star from a multiple star system, unless we viewed the system edge on and could detect eclipsing. Or, as you suggest, by some spectroscopic features, depending on the stellar types involved.
How far? What's the minimum angular separation needed to cover more than 1 pixel in a CCD? Or is that the wrong measurement?
What actually happens is that point sources cover a number of pixels, and if you plot the intensity profile you can usually determine if it's a true point source or a very small extended source. Star extraction tools that are used for astrometry and image solving are quite good at distinguishing stars from clusters and galaxies, when to our eyes they look virtually the same in images.

The point here is that we are rarely confused by detectable stars within galaxies that are close enough to yield views like we see today (and usually see in galaxy images where the galaxy is hundreds or thousands of pixels across).
Chris

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Ann
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Re: APOD: Unusual Spiral Galaxy M66 from Webb (2023 Aug 29)

Post by Ann » Thu Aug 31, 2023 5:30 am

AVAO wrote: Tue Aug 29, 2023 4:51 pm
Ann wrote: Tue Aug 29, 2023 6:09 am ...
I found another version of the JWST portrait of M66, processed by another person. And as long as everything we see is infrared light, we can map it to whatever visible colors we want to, right?
...
Ann
ThanX Ann

I like this version of "Go Webb! (Unofficial)".
Filters: F770W Blue; F1000W Cyan; F1130W Yellow; F2100W Red (slightly color temp adjusted overall)
But well, depending on which filters are transferred to RGB, the result is different again.
big:https://live.staticflickr.com/65535/526 ... 24a_o.png

However, I can find few images on the net that use the "official" JWST filter assignment. This would enable better scientific comparability. But depending on that, spatiality and depth are then lost.
Image
https://jwst-docs.stsci.edu/jwst-mid-in ... ingfilters
Nice bluish M66, AVAO! Thanks! And thank you for showing us the official JWST filter assignment, even though it rarely seems to be used.

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Re: APOD: Unusual Spiral Galaxy M66 from Webb (2023 Aug 29)

Post by johnnydeep » Thu Aug 31, 2023 1:27 pm

Chris Peterson wrote: Wed Aug 30, 2023 9:01 pm
johnnydeep wrote: Wed Aug 30, 2023 8:42 pm
Chris Peterson wrote: Wed Aug 30, 2023 7:24 pm

A cluster of stars would have to be awfully far away to look like a point source. Farther than any of these relatively nearby galaxies that we're looking at. It's likely that we couldn't distinguish a single star from a multiple star system, unless we viewed the system edge on and could detect eclipsing. Or, as you suggest, by some spectroscopic features, depending on the stellar types involved.
How far? What's the minimum angular separation needed to cover more than 1 pixel in a CCD? Or is that the wrong measurement?
What actually happens is that point sources cover a number of pixels, and if you plot the intensity profile you can usually determine if it's a true point source or a very small extended source. Star extraction tools that are used for astrometry and image solving are quite good at distinguishing stars from clusters and galaxies, when to our eyes they look virtually the same in images.

The point here is that we are rarely confused by detectable stars within galaxies that are close enough to yield views like we see today (and usually see in galaxy images where the galaxy is hundreds or thousands of pixels across).
Ok, got it.
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