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Originally Posted by gregbradley
A magnificent image and great contribution. Well done.
I would conjecture the Ha is in the Milky Way as average galaxy images don't show surrounding Ha clouds and the distances involved would be mind boggling. The clouds would be many hundreds of times larger than Cent A itself. Whilst possible it just doesn't seem likely.
The Milky Way on the other hand is chock full of Ha clouds as a wide angle shot reveals.
Also Ha surrounding a distant galaxy, where would the ionizing radiation come from?
Love that technique. Just when you think you have seen it all in this game someone posts an image like yours!
Greg.
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Thanks Greg! You raise some very good points 👍 I agree it is likely some/all of the Ha is related to the Milky Way but the gas halos around galaxies are amazingly large. For example, the Ha cloud that was discovered near M82 is 44kpc from the galaxy, which is a similar distance to the inner ring of clouds in my image 😳
As to ionisation sources, the Ha could be photo-ionised from local or background UV radiation, from starburst activity from CenA, from AGN outflows (likely with CenA), or from shock ionisation from infalling gas. It is also possible the ionisation is a light echo from a previous more active starburst period or AGN outflows. Getting some spectroscopy done would be great and would give a few clues about the ionisation mechanism 😀
Cheers, Mat