You have supplied information in relation to Patrick Gahan. I have checked www.findmypast.ie and I see a record of 180 male passengers being shipped to New South Wales. One is recorded as "Patrick Gahan. 15 years, Catholic who was being transported for burglary. His native county is recorded as "County Dublin". Convicted on March 6th 1840 in Dublin City and the sentence was 7 years. The name of the ship was King William and the Master was George Thomas. The arrival date August 17th 1840. Had he any siblings?