The paper cited in this report stated "We use ultraviolet absorption measurements of Si ii, Si iii, Si iv, C ii, and C iv from the Hubble Space Telescope/Cosmic Origins Spectrograph and O vi from the Far Ultraviolet Spectroscopic Explorer to provide an unparalleled look at how the physical conditions and metals are distributed in the CGM of M31. "
Another report stated, "We find the inner shell that extends to about a half million light-years is far more complex and dynamic," explained study leader Nicolas Lehner of the University of Notre Dame in Indiana. "The outer shell is smoother and hotter. This difference is a likely result from the impact of supernova activity in the galaxy's disk more directly affecting the inner halo.", Hubble maps giant halo around Andromeda Galaxy, https://phys.org/news/2020-08-hubble-giant-halo-andromeda-galaxy.html
My observation. The observation and explanation of metals found in M31 halo uses r-process and s-process to explain the metals and avoid BB problems, perhaps. Metals in M31 halo can also be interpreted as primordial thus metals in the halo from the start. However, this approach opens up problems with BB, Population III stars, and cosmic evolution using the r-process, s-process to explain the presence of metals found in the halo. The M31 halo with metals could be interpreted as no primordial gas clouds from BB that formed the M31 halo but the gas was already metal polluted. r-process and s-process tweaks are needed to reconcile the observations with BB cosmology and the report does this.