Extraplanar HII regions in the edge-on spiral galaxies NGC 3628 and NGC 4522 Y. Stein, D. J. Bomans, A. M. N. Ferguson and R.-J. Dettmar A&A, 605 (2017) A5 Published online: 29 August 2017 DOI: 10.1051/0004-6361/201730589