Andhra Brahmins Migrated from Tamil Nadu? Surnames

My view is that Brahmins, being an integral part of Sanathana Dharma, were present in the North and the South right from the earlier ages. And Lord Rama's ancestor Satyavrata Manu migrated from the South to the North and his offspring established the Ikshvahu dynasty. However evidence suggests that the Brahmins initially settled around the Cauvery River in Tamil Nadu, which was ruled by the Chola dynasty whose ancestors were the Surya Dynasty, and the Cholas belong to Kasyapa Gotra. Please read my post on this. Brahmins migrated , for unknown reasons to Andhra Pradesh, around 1400AD.

Manu Rama’s Ancestor Migrated From South India 5000 BC

If the first migration was from the East, how come there were people already living in these areas? From where did they come? For more on this, read my post Rama's ancestor Dravida. But the Puranas and Tamil Classics provide information that can be checked with astronomical phenomenon, cross checked with other literature, archeological findings. One such information is the so-called Legends of the Tamil Sangams. Sangams are Poets' Conclaves held by the Tamil Kings. There were three such Sangams held.