Fáinne Geal an Lae. It means literally "The bright ring of day". There are two songs of this name, they predate Kavanagh by 250 and 100 years respectively. It is the later one by Edward Walsh which is translated into English as The Dawning of the Day.

Kavanagh would have been aware of this, and included the phrase "The Dawning of the Day" in his poem Raglan Road. It is thought that he had this tune in mind when he wrote it.

Source 1

Source 2

I know nothing about Connellan's earlier Fáinne Geal an Lae.