Outer edges of face-on spiral galaxies - Deep optical imaging of NGC 5923, UGC 9837 and NGC 5434M. Pohlen, R.-J. Dettmar, R. Lütticke and G. AronicaA&A, 392 3 (2002) 807-816DOI: https://doi.org/10.1051/0004-6361:20020994