The affix ya comes in the sense of 'who deserves that' after the word soma in the Accusative -2nd case in construction, in the chandas (Vedas).,
Thus सोममर्हन्ति = सौम्या ब्राह्मणाः \The Brahmanas who deserve Soma\ i. e. honorable and learned, and worthy of performing sacrifices. The difference between यत् and घ is in accent.,