Ionized gas in the Nuclear Bulge

N.J.Rodríguez-Fernaández1, J. Martín-Pintado2, A. Fuente3, P. de Vicente3, T. Wilson4, S. Hüttemeister5

1 LERMA, Observatoire de Paris, 61, Av. de l'Observatoire, 75014, Paris, France
2 Instituto de Estructura de la materia, CSIC, Serrano 121, Spain
3 Observatorio Astronómico Nacional, IGN, Apdo. 1143, 28800 Alcalá de Henares, Spain
4 Max-Planck Institute für Radioastronomie, Bonn, Germany
5 Bochum University, Bochum, Germany

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The interstellar medium in the central 600 pc of the Galaxy (hereafter Nuclear Bulge, NB) is mainly neutral and molecular. Is there ionized gas associated to the molecular clouds of the NB? In our contribution we will present fine structure lines observations made by the LWS and SWS instruments onboard the Infrared Space Observatory (ISO) toward a sample of clouds distributed along the NB. We also present hydrogen radio recombination lines observations of those clouds made with the IRAM 30m millimeter telescope. The cloud sample was selected as molecular peaks located far from known thermal radio continuum sources. The radio recombination lines observations seem to confirm the lack of ionized gas in the line of sight of the molecular clouds. We have not detected emission in any of the sources. However, the fine structure line observations in the infrared reveal the presence of ionized gas in all of the clouds. In some of the clouds we have even detected lines from Ne III or N III. We discuss the properties of this ionized gas and those of the ionizing radiation with emphasis on the ionization structure in the Arc region.