You are right - PIE cluster -rkt- becomes Common
Celtic -rt- (and then Welsh -rth-).
I am not familiar with this Celtiberian word arsias
- can you tell me where it comes from? The -s- in Celtiberian may actually stand
for a -ts- sound. The feminine suffix -(i)as is usually the genitive singular or
accusative plural.
-C. Gwinn