Comparing Radio and X-Ray Galaxies: Redshift vs. Emission Mechanism

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Discussion Overview

The discussion revolves around the characteristics that distinguish radio galaxies from X-ray galaxies, particularly focusing on the concepts of redshift and emission mechanisms. Participants explore the implications of distance, frequency, and the nature of emissions from these galaxies.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants question whether all radio galaxies are approximately the same distance from us and whether their receiving frequency is exclusively in the radio band.
  • One participant notes that while radio galaxies are not all at the same distance, the difference in redshift between nearby and extremely distant galaxies is relatively small compared to the difference between radio and X-ray emissions.
  • There is a discussion about the definition of a radio galaxy, with some participants suggesting that it should be characterized by its emission in the radio band, while others argue that it also emits in other wavelengths.
  • One participant mentions Centaurus A as a classic example of a radio galaxy, indicating that it emits significant radiation across multiple bands, including radio, visible, and X-rays.
  • Another participant expresses confusion about the categorization of radio galaxies, questioning what specifically distinguishes them if they emit across various frequencies.
  • Clarifications are made regarding the term "receiving frequency," with one participant suggesting that there was a misunderstanding of this concept in earlier posts.

Areas of Agreement / Disagreement

Participants express differing views on the criteria that define a radio galaxy, particularly regarding the significance of its emissions across different frequency bands. The discussion remains unresolved, with multiple competing perspectives present.

Contextual Notes

There are unresolved questions regarding the definitions of terms like "receiving frequency" and the implications of redshift on the categorization of galaxies. The discussion reflects varying interpretations of what constitutes a radio galaxy.

shirin
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Are all the radio galaxies in the (approximarely) same distance from us? And is the reciveing frequency from all of them in radio band?
I am wondering whether the difference between a radio and x-ray galaxy is their redshift or their emission mechanism ?
 
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shirin said:
Are all the radio galaxies in the (approximarely) same distance from us?
No, but the difference between "nearby" and "extremely far away" is just a factor of 10 in redshift. The difference between radio and xrays is something like a factor of 100000000000. Also, the observations get corrected for redshift for obvious reasons.
 
When we say a galaxy is a radio-galaxy, does it mean that its reciving frequency is in radio band?
Is it correct that all of observibg synchrotron activities are in radio band? Or we can observe this activity in other bands too?
 
shirin said:
When we say a galaxy is a radio-galaxy, does it mean that its receiving frequency is in radio band?

no, the opposite ... its an intense emitter of RF, visible and X-rays
Centaurus A radio galaxy is a classic object

here's a set of images showing the galaxy at different wavelengths

Cen_A_multiwavelength_7.jpg
Dave
 
davenn said:
no, the opposite ... its an intense emitter of RF, visible and X-rays
Centaurus A radio galaxy is a classic object

here's a set of images showing the galaxy at different wavelengths

View attachment 89998Dave

So I don't understand what categorizes a galaxy as a "radio galaxy". If it has radiation in other bands too and it is not its received frequency to us, then what does distinguish it as a "radio" galaxy?
 
shirin said:
So I don't understand what categorizes a galaxy as a "radio galaxy". If it has radiation in other bands too and it is not its received frequency to us, then what does distinguish it as a "radio" galaxy?

Radio galaxies emit large amounts of radiation in the RF band of the EM spectrum. Much more than the usual galaxy does. I think davenn misunderstood what you mean by 'receiving frequency'.
 
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Drakkith said:
I think davenn misunderstood what you mean by 'receiving frequency'.

hahaha uh huh
for the first part of my answer yes I did mis-read ... put it down to being exhausted
 

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