I research the Irish Family History Foundation's database. It contains 12,000,000 surviving rcds for abt 65% of Irish counties. Rcds are increasingly sparse B4 1840, rare B4 1800.
Note 1 - Without a KNOWN county, the chance of an ancestor's rcds NOT being in this database is AT LEAST 35%.
Note 2 - Only 1/2 of Co. Cork's rcds are in this database.
Note 3 - The RC church kept control over most parish rcds from Tipperary (north). These are ONLY available thru the Tipperary Family History Research center at a substantial fee (regardless of outcome).
For Tho(mas) Ratigan B ???? Co. Galway, with the father's forename unknown, the earliest rcd I found was in 1819.
For Tho(mas) Ratigan M 1834 +/- 4 yrs Co. Galway, I found 1 rcd in 1837, Dunmore RC parish. This has a small chance of being for your ancestor. A view of the detailed rcd MAY show that the bride's name was Catherine. Even if it does, Catherine was second in popularity only to the ubiquitous Mary. Therefore, it may be a false positive. You will need an exact DOB, parent(s) name(s), and/or placename(s) to validate the rcd.
Google the Foundation's name to lead you to this database. Register, opt to be notified as rcds are added and browse. Pls post your search results to my genforum msg.