Johan Arnesen m. Emilie Fossum

I can find Johan Arnesen b. 1839 Fredrikstad in the 1865 and 1875 census. He was married to Emilie Fossum b. 1843 Christiania. I don't see children for them either? I think they might have moved to USA but can not find ship records or census records to back that up. Any ideas where to look for them?