APOD: NGC 4632: Galaxy with a Hidden Polar... (2023 Sep 13)

[APOD Robot]

NGC 4632: Galaxy with a Hidden Polar Ring

Explanation: Galaxy NGC 4632 hides a secret from optical telescopes. It is surrounded by a ring of cool hydrogen gas orbiting at 90 degrees to its spiral disk. Such polar ring galaxies have previously been discovered using starlight. However, NGC 4632 is among the first in which a radio telescope survey revealed a polar ring. The featured composite image combines this gas ring, observed with the highly sensitive ASKAP telescope, with optical data from the Subaru telescope. Using virtual reality, astronomers separated out the gas in the main disk of the galaxy from the ring, and the subtle color gradient traces its orbital motion. Why do polar rings exist? They could be material pulled from one galaxy as it gravitationally interacts with a companion. Or hydrogen gas flows along the filaments of the cosmic web and accretes into a ring around a galaxy, some of which gravitationally contracts into stars.

<< Previous APOD

This Day in APOD

Next APOD >>

[AVAO]

NGC 4632: Galaxy with a Hidden Polar Ring

Explanation: Galaxy NGC 4632 hides a secret from optical telescopes. It is surrounded by a ring of cool hydrogen gas orbiting at 90 degrees to its spiral disk. Such polar ring galaxies have previously been discovered using starlight. However, NGC 4632 is among the first in which a radio telescope survey revealed a polar ring. The featured composite image combines this gas ring, observed with the highly sensitive ASKAP telescope, with optical data from the Subaru telescope. Using virtual reality, astronomers separated out the gas in the main disk of the galaxy from the ring, and the subtle color gradient traces its orbital motion. Why do polar rings exist? They could be material pulled from one galaxy as it gravitationally interacts with a companion. Or hydrogen gas flows along the filaments of the cosmic web and accretes into a ring around a galaxy, some of which gravitationally contracts into stars.

<< Previous APOD

This Day in APOD

Next APOD >>

“The findings suggest that one to three per cent of nearby galaxies may have gaseous polar rings, which is much higher than suggested by optical telescopes. Polar ring galaxies might be more common than previously thought.”

“NGC 4632 is one of two polar ring galaxies we’ve identified from 600 galaxies that were mapped in our first small WALLABY survey."

“Using ASKAP over coming years we expect to reveal more than 200,000 hydrogen-rich galaxies, among them many more unusual galaxies like these ones with polar rings.”

"Why polar rings exist is still a puzzle to astronomers. One possible explanation is that their stellar rings, which appear blended with gas clouds, are shredded material from a passing galaxy. Another possibility is that hydrogen gas flows along the filaments of the cosmic web and accretes into a ring around a galaxy, possibly forming stars during this process."

...what great perspectives...

https://www.icrar.org/first-wallaby
https://www.icrar.org/polar-rings

[Ann]

NGC 4632: Galaxy with a Hidden Polar Ring Credit: Jayanne English (U. Manitoba), Nathan Deg (Queen's University) & WALLABY Survey, CSIRO/ASKAP, NAOJ/Subaru Telescope

---

My first question when I see a picture like this, is always, What kind of a galaxy is this?

Here is a Sloan Digital Sky Survey picture of NGC 4632:

---

A few points here. NGC 4632 has a small and faint yellow center. Its disk is dominated by a fairly nondescipt mixture of small stars of different populations. There are some green splotches which are really red emission nebulas, birth sites of young stars, which are shown as green in the SDSS palette. There are also a few blurry blue regions which represent somewhat older clusters or associations of young stars, where no red nebulas are present. As for the overall shape of this galaxy, the spiral pattern is not very well developed in NGC 4632.

Conclusion: NGC 4632 looks like a smallish galaxy to me, mostly because I don't expect a large galaxy to have such a puny yellow center (although I must admit that SDSS images don't usually make galactic centers look extremely bright).


Let's compare NGC 4632 with two other galaxies seen in the SDSS palette:

NGC 2976. Image credit: SDSS/Donald Pelletier

---

NGC 1087. Credit: SDSS.

---

NGC 2976 is puny indeed. You can barely see the yellow core. There is also no spiral pattern at all. According to Wikipedia, NGC 2976 is midway in size between the Large and Small Magellanic Clouds, which does make it quite small.

As for NGC 1087, it has a very short but rather bright bar. The disk is rather full of green and blue blobs, which means that there is a good amount of star formation here. The spiral pattern is not very well developed at all, but there is what looks like a very obvious "torque" in this galaxy, as if the bar itself was turning and dragging the entire galactic disk along with it.

According to my software, the distance to NGC 1087 is 76 million light-years, and Wikipedia mostly agrees with that (~80 million light-years). My software says that the brightness and distance of NGC 1087 makes it similar in brightness to the Milky Way. Yes, maybe.

My software also suggests that the brightness and distance of NGC 4632 (11.8 in V mag, 74 million light-years) makes it about 70% the brightness of the Milky Way. It looks smaller to me.


Okay! Polar ring galaxy! Two examples are NGC 4650A and NGC 660:

Polar ring galaxy NGC 660. Credit: Gemini Observatory, AURA, NASA

---

Polar ring galaxy NGC 4650A. Credit: The Hubble Heritage Team (AURA/STScI/NASA/ESA)

---

Maybe in the future the polar ring of gas around NGC 4632 will collapse into a ring of stars, giving NGC 4632 an upgraded, very impressive appearance?

Ann

[AVAO]

NGC 4632: Galaxy with a Hidden Polar Ring Credit: Jayanne English (U. Manitoba), Nathan Deg (Queen's University) & WALLABY Survey, CSIRO/ASKAP, NAOJ/Subaru Telescope

---

My first question when I see a picture like this, is always, What kind of a galaxy is this?

Here is a Sloan Digital Sky Survey picture of NGC 4632:

---

A few points here. NGC 4632 has a small and faint yellow center. Its disk is dominated by a fairly nondescipt mixture of small stars of different populations. There are some green splotches which are really red emission nebulas, birth sites of young stars, which are shown as green in the SDSS palette. There are also a few blurry blue regions which represent somewhat older clusters or associations of young stars, where no red nebulas are present. As for the overall shape of this galaxy, the spiral pattern is not very well developed in NGC 4632.

Conclusion: NGC 4632 looks like a smallish galaxy to me, mostly because I don't expect a large galaxy to have such a puny yellow center (although I must admit that SDSS images don't usually make galactic centers look extremely bright).


Let's compare NGC 4632 with two other galaxies seen in the SDSS palette:

NGC 2976. Image credit: SDSS/Donald Pelletier

---

NGC 1087. Credit: SDSS.

---

NGC 2976 is puny indeed. You can barely see the yellow core. There is also no spiral pattern at all. According to Wikipedia, NGC 2976 is midway in size between the Large and Small Magellanic Clouds, which does make it quite small.

As for NGC 1087, it has a very short but rather bright bar. The disk is rather full of green and blue blobs, which means that there is a good amount of star formation here. The spiral pattern is not very well developed at all, but there is what looks like a very obvious "torque" in this galaxy, as if the bar itself was turning and dragging the entire galactic disk along with it.

According to my software, the distance to NGC 1087 is 76 million light-years, and Wikipedia mostly agrees with that (~80 million light-years). My software says that the brightness and distance of NGC 1087 makes it similar in brightness to the Milky Way. Yes, maybe.

My software also suggests that the brightness and distance of NGC 4632 (11.8 in V mag, 74 million light-years) makes it about 70% the brightness of the Milky Way. It looks smaller to me.


Okay! Polar ring galaxy! Two examples are NGC 4650A and NGC 660:

Polar ring galaxy NGC 660. Credit: Gemini Observatory, AURA, NASA

---

Polar ring galaxy NGC 4650A. Credit: The Hubble Heritage Team (AURA/STScI/NASA/ESA)

---

Maybe in the future the polar ring of gas around NGC 4632 will collapse into a ring of stars, giving NGC 4632 an upgraded, very impressive appearance?

Ann

ThanX Ann for your exciting explanations.

Apparently no one wants to discuss this very exciting innovations.

The fact that it is possible to derive the 3D structure of the surrounding hydrogen cloud from the observations is an absolute milestonein deepsky astronomy.

The structure also clearly shows that the previous model of a ring needs to be corrected. It clearly represents two twisted gas strands and clearly speaks for a new model: "Another possibility is that hydrogen gas flows along the filaments of the cosmic web and accretes into a ring around a galaxy, possibly forming stars during this process."

This means that the current standard theory of the formation of galaxies continues to falter.

Jac

[orin stepanek]

PolarRing_Askap_960.jpg

Ring makes the Galaxy look special!

dog-playing-tug.jpg

Doggy playing tug of war!

[Uncle Jeff]

When I first saw the picture, I thought it was a coincidence of looking down the throat of a nearby planetary nebula that just happened to frame a distant spiral galaxy.

What work has been done to measure the distance to the ring to prove that it is in fact associated with the galaxy and not an amazing coincidence of alignment?

[Roy]

As Ann has shown, this doesn’t look like a polar ring galaxy. What’s going on here? The ASKAP site shows that it is an array of radio astronomy dishes, heavily computerized to convert the radio waves into visual images. They use something called “virtual reality” to locate and view the images. The NGC 4632 image is from the optical Subaru telescope. So we are presented with a composite image. The Subaru site is in Japanese, which is hard to read unless you have studied the language (aside: complex Kanji characters from Chinese, Hiragana characters for syllables, and a set of Katakana characters for foreign words.)
So, it could be that the radio image is misplaced, obscures another object, or is computerized in some internal way..I know the astronomers are doing their best, but I do not see how the two images are related.

[Chris Peterson]

As Ann has shown, this doesn’t look like a polar ring galaxy. What’s going on here? The ASKAP site shows that it is an array of radio astronomy dishes, heavily computerized to convert the radio waves into visual images. They use something called “virtual reality” to locate and view the images. The NGC 4632 image is from the optical Subaru telescope. So we are presented with a composite image. The Subaru site is in Japanese, which is hard to read unless you have studied the language (aside: complex Kanji characters from Chinese, Hiragana characters for syllables, and a set of Katakana characters for foreign words.)
So, it could be that the radio image is misplaced, obscures another object, or is computerized in some internal way..I know the astronomers are doing their best, but I do not see how the two images are related.

They are just images in two different ranges of the EM spectrum. The location of the radio emissions is rigorously determined.

[johnnydeep]

The "polar ring" plane shown here looks to be more like 45 degrees offset from the plane of the rest of the galaxy, not 90 degrees as stated. Or am I being deceived by perspective?