APOD: Galaxies in Pegasus (2014 Oct 23)

[APOD Robot]

Galaxies in Pegasus

Explanation: This wide, sharp telescopic view reveals galaxies scattered beyond the stars and faint dust nebulae of the Milky Way at the northern boundary of the high-flying constellation Pegasus. Prominent at the upper right is NGC 7331. A mere 50 million light-years away, the large spiral is one of the brighter galaxies not included in Charles Messier's famous 18th century catalog. The disturbed looking group of galaxies at the lower left is well-known as Stephan's Quintet. About 300 million light-years distant, the quintet dramatically illustrates a multiple galaxy collision, its powerful, ongoing interactions posed for a brief cosmic snapshot. On the sky, the quintet and NGC 7331 are separated by about half a degree.

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[Ann]

Oh, that's a great picture! So glad to see it!

One thing that fascinates me about the Deer Lick Group (the scattered group of distant galaxies near large galaxy NGC 7331), when you compare it with the true members of Stephan's Quintet, is that all these galaxies are more or less the same apparent size. Okay, the Deer Lick Group members look a bit bigger than the Sephan's Quintet ones, but not by much. This suggests to me that they are at relatively similar distances from us. And if we think of them like that, then we can really see how compact Stephan's Quintet is. The Deer Lick Group is probably a relatively "typical" galaxy group, unlike Stephan's Quintet, which is like a galactic train wreck. (Actually the Deer Lick group looks like a rather tight group too, and its members have probably had a lot of interaction, judging from the fact that there is little star formation here.)

I also like seeing the very blue color of NGC 7320, the foreground dwarf galaxy which is only masquerading as a member of Stephan's Quintet. Small starforming galaxies like NGC 7320 are typically quite blue. The reason is probably that they haven't built up a large population of old red and yellow stars, and moreover they have undergone so few episodes of star formation that they are still relatively metal-poor (that is, they contain low levels of elements heavier than hydrogen and helium). And metal-poor stars are typically bluer than metal-rich ones.

What a fine picture!

Ann

[Indigo_Sunrise]

Oh, that's a great picture!

/snip


x2
Very great indeed!

[TNT]

That's an awesome shot of Stephan's Quintet in the corner! That small group of galaxies has always been intriguing to me...

[Cousin Ricky]

It should probably be noted that only 4 of the galaxies in Stephan's Quintet are interacting with each other.

[Chris Peterson]

It should probably be noted that only 4 of the galaxies in Stephan's Quintet are interacting with each other.

Well, technically, every galaxy we see in this image is interacting with all the others. Do you mean that only four are gravitationally bound into closed orbits about each other?

[visual_astronomer]

This is a favorite observing target of mine - I can't quite fit both the Deer Lick group and Stephen's quintet into one field of view, but it's close. Just a little panning and I can move from one to the other. The photo reveals a lot of galactic dust which is of course not visible, but it makes the image very interesting. A beautiful image indeed!

[Ann]

Click to view full size image

It should probably be noted that only 4 of the galaxies in Stephan's Quintet are interacting with each other.

Actually, there really seems to be five members in Stephan's Quintet. The fifth member is some distance away from the others, but the tidal tail of one of the main galaxies points towards it.

The blue foreground galaxy is not a member, however.

Ann

[Cousin Ricky]

It should probably be noted that only 4 of the galaxies in Stephan's Quintet are interacting with each other.

Well, technically, every galaxy we see in this image is interacting with all the others. Do you mean that only four are gravitationally bound into closed orbits about each other?

And people tell me that I'm pedantic.

[Chris Peterson]

And people tell me that I'm pedantic.

Wear it with pride!

[starsurfer]

And people tell me that I'm pedantic.

Wear it with pride!

starsurfer approves of the exclamation mark!

[AeWObservatory]

Thank you so much to all the people who have seen and commented on our image.
Best Regards