My Great-Grandfather Thomas McCormack born Dublin 1841

Hi - My G Grandfather Thomas McCormack was born in Dublin in 1841 and migrated to Tasmania with his family when still a child. He was a great writer, winning prizes for his essays in the NZ Tablet, a Catholic journal, and married Elizabeth Ann Briggs, born 1849 in Hobart, the daughter of two English convicts who had been transported there. They had six children, including my grandfather Louis Francis McCormack (1884-1954). Thomas owned a successful metalworking business in Dunedin after migrating to NZ as a young man and died in Dunedin in 1923. However we have no information about his parents, why the family left for Australia, or how old he was when he left Ireland. In one of his essays he described travelling on a coach between Launceston and Hobart, talking to a distinguished gentleman, who however the other passengers were shunning, and who turned out to be the hangman, coming to "turn off" some convicts. Any information about Thomas MCCormack's family would be much appreciated.