M31 halo paper - question on metallicity

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    Halo Paper
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The discussion centers on a paper that presents evidence of a halo of ionized gas and heavier elements around the Andromeda galaxy, estimating the mass of the halo's metal component at 2 million solar masses. Various hypotheses are proposed regarding the origin of these heavier elements, including creation by supernovae in situ, expulsion from nearby supernovae, hypervelocity stars, and remnants of galactic collisions. The presence of rogue hypervelocity stars is mentioned as a potential source, although their connection to the heavy elements is unclear. The conversation highlights the need for data or models that explain the existence of these heavy elements, particularly since current supernova activity in the region is not evident. Overall, the discussion seeks to clarify the mechanisms behind the observed metallicity in the Andromeda halo.
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http://iopscience.iop.org/0004-637X/804/2/79/pdf/0004-637X_804_2_79.pdf
The report finds evidence for a halo of ionized gas and small amounts of other heavier elements, in a very large halo around the Andromeda galaxy. The report estimates the mass of the CGM halo's metal component at 2 million solar masses.

Ok.

So here are some ways to explain how those "extra" heavier elements got out there:
created by supernovae in situ
expulsion from supernovae closer to home
hypervelocity stars(?)
remnants of galactic collisions

I am aware of one report (cannot get the citation) on the presence of rogue hypervelocity stars far from the center of mass of our own Milky Way. These could be larger staller mass objects, I do not know.

Most references - like Wikipedia - cite models with Population I stars making up most of the sparse stellar population out there. So, what hypothesis/explanation/data accounts for those heavy elements?

Heavy elements are derived from supernovae, which AFAIK does not appear to be happening out there right now.

Thanks for any corrections.
 
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