Ionized gas at the edge of the central molecular zone W. D. Langer, P. F. Goldsmith, J. L. Pineda, T. Velusamy, M. A. Requena-Torres and H. Wiesemeyer A&A, 576 (2015) A1 Published online: 13 March 2015 DOI: 10.1051/0004-6361/201425360