Stephan's Quintet

1. Mar 5, 2006

Nacho

A Shocking Surprise in Stephan's Quintet

The Spitzer Telescope views Stephan's Quintent. I remember reading a writeup Halton Arp had about this a time back (please, this is not the place for "shots" against him), that he thought the bottom left galaxy was actually a member of the group, but had a discordant redshift .. and it went against conventional wisdom.

Here's a couple of quotes in the article, with my emphasis:

It appears to me the "green arc" is in front of the galaxy that is supposed to be a foreground object. I suppose since it is of a different wavelength of light, it could bleed through a foreground galaxy that didn't emit very much of that wavelength .. but it all looks fishy to me!

I guess it could be that the "green arc" they are talking about is not the large green filament in the center of the picture (and that would be an even closer object, perhaps in our galaxy) but the small green-to-red arc in the interacting galaxy to the right that makes a smilely face with the 2 concentrated light objects above it.

What am I missing here!?!

2. Mar 5, 2006

SpaceTiger

Staff Emeritus
It looks to me like that "green object" (H$\alpha$ light) only extends as far as the edge of the foreground galaxy. Where do you see them overlapping?

3. Mar 5, 2006

Nacho

The large pink galaxy on the bottom left. It's supposed to be a spiral, but by its orientation it takes a two-dimensional shape of an oval. The "green object" takes a pretty good bite out of the top-right side of it.

4. Mar 5, 2006

neutrino

I think it's nothing more than a line-of-sight-illusion. I may be wrong, but I think such a powerful shockwave interacting with another galaxy might not remain "green". Also it appears that the foregroud galaxy is not disturbed by the shockwave.

5. Mar 5, 2006

Nacho

Good point about there not being a distruption .. that makes sense. How could it be a line-of-sight-illusion though?

6. Mar 5, 2006

SpaceTiger

Staff Emeritus
What happens when you view a disk that is inclined relative to your line of sight?

Well, I only see a very tiny region where there appears to be any overlap, and this would be expected if the foreground galaxy's disk were obscuring the H$\alpha$ light. The green changes into blue right at the edge, and we expect the blue (near-infrared light) from the foreground galaxy's disk.

I wouldn't expect the shock wave to have a big impact on any of the galaxies (it has very low mass) -- rather, it is itself an indication of the gravitational interaction that's already occurring. Notice, in fact, that the foreground galaxy is very smooth with no prominent spiral waves. If it were gravitationally interacting, we would expect it to be clumpy and distorted like the others.

7. Mar 5, 2006

Nacho

I see now. If you do forget about the blue for a moment, there is very little if any overlap on the green. It seemed to me the blue was a continuation of the green, not part of the spiral.

8. Mar 6, 2006