Extra-planar gas in the spiral galaxy NGC 4559 C. V. Barbieri, F. Fraternali, T. Oosterloo, G. Bertin, R. Boomsma and R. Sancisi A&A, 439 3 (2005) 947-956 Published online: 12 August 2005 DOI: 10.1051/0004-6361:20042395