MarkBour wrote: ↑Wed Jan 16, 2019 6:08 pm
Ann wrote: ↑Wed Jan 16, 2019 11:50 am
As you can see, IC 342 is a bit more irregular than M74. That suggests that IC 342 is more affected by star formation than M74. Either there is actually more star formation going on in IC 342 than in M74, or, alternatively, IC 342 is a less massive galaxy than M74 so that it more easily gets distorted by the extremely strong winds of massive star formation.
That's an interesting take on this. All I have heard so far goes the other direction: Gravitational "events" cause distortions, and then disruption of gas clouds, which then brings on bursts of star formation. I did not think that star formation could cause spiral arm distortions on the galactic scale. (Meaning that they could deform a spiral arm enough that it would be noticeable to an observer looking at an image of a galaxy at this scale.)
NGC 1313. Photo: Robert Gendler.
M101. Photo: Robert Gendler.
The idea that galaxies get distorted from a lot of star formation is my amateur impression from looking at pictures of a lot of spiral galaxies and irregular galaxies. Irregular galaxies, as you know, are practically always small and low in mass, and they undergo a lot of star formation and become absolutely contorted because of that.
NGC 1313 is a smallish galaxy, somewhat halfway between a spiral and an irregular galaxy, and it is very distorted. Interestingly, it appears to be pretty much alone in its own neighbourhood, so its own shenanigans must have played a big role in making its shape so weird. (But I guess it just might have collided with, or been tidally disrupted by, a clump of dark matter passing by.)
M101 is of course a huge galaxy, but my impression is that it is lightweight for its size. Surely it must have been disturbed by interaction with another galaxy, but my guess is that its massive star formation has affected its shape, too.
M74. Isaac Newton Group of Telescopes.
Anyway, now that I look at the two pictures in my first post of galaxies M74 and IC 342 on my computer at home, the two galaxies look about equally distorted. Maybe that is because I can see the outer, low-luminosity arms of M74, while no such arms can be seen in IC 342.
But take a look at M74 again. See how regular its bright arms are, except for a strange "arc" at upper right, where the spiral arm "bends the wrong way". There appears to be a lot of star formation going on in the rims of that arc.
What caused the arc? Maybe a very powerful supernova, or even more than one supernova?