by Ann » Wed Sep 13, 2023 6:29 am
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 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:
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
[img3="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"]https://apod.nasa.gov/apod/image/2309/PolarRing_Askap_960.jpg[/img3]
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:
[img3=""]https://upload.wikimedia.org/wikipedia/commons/5/50/NGC4632_-_SDSS_DR14.jpg[/img3]
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:
[float=left][img3="NGC 2976. Image credit: SDSS/Donald Pelletier"]https://upload.wikimedia.org/wikipedia/commons/thumb/9/9e/NGC_2976_SDSS.jpg/1200px-NGC_2976_SDSS.jpg?20181031234140[/img3][/float][float=right][img3="NGC 1087. Credit: SDSS."]https://upload.wikimedia.org/wikipedia/commons/5/5b/NGC1087_-_SDSS_DR14.jpg[/img3][/float]
[clear][/clear]
NGC 2976 is puny indeed. You can barely see the yellow core. There is also no spiral pattern at all. According to [url=https://en.wikipedia.org/wiki/NGC_2976]Wikipedia[/url], 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 [url=https://en.wikipedia.org/wiki/NGC_1087]Wikipedia[/url] 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:
[float=right][img3="Polar ring galaxy NGC 660. Credit: Gemini Observatory, AURA, NASA"]https://upload.wikimedia.org/wikipedia/commons/thumb/9/9d/NGC_660_Polar_Galaxy_Gemini_Observatory.jpg/1280px-NGC_660_Polar_Galaxy_Gemini_Observatory.jpg[/img3][/float][float=left][img3="Polar ring galaxy NGC 4650A. Credit:
The Hubble Heritage Team (AURA/STScI/NASA/ESA)"]https://cdn.spacetelescope.org/archives/images/large/opo9916a.jpg[/img3][/float]
[clear][/clear]
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