Summary on Authorship
nThat Luke wrote the Gospel ascribed to him is the unanimous opinion of tradition & of the titles on extant manuscripts.
nNone of the remarks for Luke are quite as early as those of Papias for Matt & Mark; but by AD 200, these are from whole Mediterranean area.
nThese traditions are consistent with the internal evidence of vocabulary & connection with Acts.
nThe Gospel is frequently mentioned third, perhaps preserving a tradition on order of authorship.