Stephan's Quintet: Spitzer Telescope Views Galaxy Cluster Shock Wave

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Discussion Overview

The discussion centers on the observations made by the Spitzer Telescope regarding Stephan's Quintet, particularly focusing on the interpretation of a shock wave and the positioning of a foreground galaxy in relation to the observed phenomena. Participants explore the implications of redshift, light wavelengths, and visual interpretations of the galaxy cluster.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants reference Halton Arp's views on the discordant redshift of the bottom left galaxy, suggesting it may be a member of the group despite conventional wisdom.
  • There is a debate about the positioning of the "green arc" and whether it is in front of the foreground galaxy or not, with some participants questioning the overlap of the green object with the galaxy.
  • One participant suggests that the green object may only extend to the edge of the foreground galaxy, raising questions about the visibility of the shock wave.
  • Another participant proposes that the observed phenomena could be a line-of-sight illusion, noting that the shock wave might not remain "green" when interacting with another galaxy.
  • Concerns are raised about the lack of disturbance in the foreground galaxy, which could indicate that it is not gravitationally interacting with the shock wave.
  • Participants discuss the implications of viewing an inclined disk and how it affects the perception of overlap between the galaxies and the shock wave.
  • There is acknowledgment that the blue light observed may not be a continuation of the green, but rather part of the foreground galaxy's disk.

Areas of Agreement / Disagreement

Participants express differing interpretations of the visual data and the implications of the shock wave's interaction with the foreground galaxy. No consensus is reached regarding the nature of the observations or the validity of the proposed interpretations.

Contextual Notes

Participants note limitations in their observations, including assumptions about the visibility of light wavelengths and the effects of gravitational interactions on galaxy morphology. The discussion remains open-ended with unresolved questions about the nature of the observed phenomena.

Nacho
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http://www.spitzer.caltech.edu/Media/releases/ssc2006-08/"

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:

This false-color composite image of the Stephan's Quintet galaxy cluster clearly shows one of the largest shock waves ever seen (green arc), produced by one galaxy falling toward another at over a million miles per hour.


One galaxy, the large spiral at the bottom left of the image, is a foreground object and is not associated with the cluster.


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?
 
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Nacho said:
It appears to me the "green arc" is in front of the galaxy that is supposed to be a foreground object.

It looks to me like that "green object" (H[itex]\alpha[/itex] light) only extends as far as the edge of the foreground galaxy. Where do you see them overlapping?
 
SpaceTiger said:
It looks to me like that "green object" (H[itex]\alpha[/itex] light) only extends as far as the edge of the foreground galaxy. Where do you see them overlapping?

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.
 
Nacho said:
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.
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.
 
neutrino said:
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.

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

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


The "green object" takes a pretty good bite out of the top-right side of it.

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[itex]\alpha[/itex] 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.
 
SpaceTiger said:
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[itex]\alpha[/itex] 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 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.
 

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