There was a question that came up on the MCM mailing list about what are these files: model_msdbdata.mdf, model_msdblog.ldf, model_replicatedmaster.mdf, model_replicatedmaster.ldf? It was pointed out that the files don’t show up in the typical DMVs and seem to not really be used at the moment.
These are the databases used as the basis for the system databases in contained availability groups. Definitely don’t touch them, just leave them be, even if you aren’t using availability groups (let alone contained).
Click through for more information on how you can find them and another warning not to mess with them.