Soghdians, Persian or Iranic?

Modern Tajik is just a Persian dialect, but Yaghnobi language which is spoken in Sughd province of Tajikistan can be considered a descendant of Sogdian, there are certainly some differences between Sogdian and Persian languages, however both of them are Iranian and you can find a large number of similar words between them, anyway Tajikistan was part of the Greater Khorasan which became the cultural center of Persians after the fall of Sassanid empire, no one can deny the role Samanids who were originated in the land of Tajiks, in the survival of the Persian culture, in fact the greatest known Persian literary figures, like Rudaki, were from this region.