This is an initial entry, hopefully I will write more in the near future.
Personally I believe there are 2 lines of Jackman's in Ireland, the reason I say this is Noel Jackman in Waterford and myself have had our DNA done and registered. We are connected a long time back, certainly not in the last 8 generations. I believe my Jackmans lived in Carlow, Wexford, Wicklow and Dublin.
Noel's branch come mainly from Kilkenny, Waterford, Tipperary, Cork, Fermanagh.
In my only family some of my uncles were registered as Chapman, which was later changed by deed pole.
If interested in finding which line your Irish Jackman relatives come from, consider contacting FTDNA and doing the test. Cost between 150 and 200 dollars,
Jamesjackman57@gmail.com