Large scale ionization of the Radio Arc region by the Quintuplet and the Arches cluster

Abstract

(Short version) We present an analysis of selected fine structure lines observed ISO toward the Radio Arc in the Galactic center region (GCR). We study the density of the ionized gas and the large scale ionization structure in a region of ~30x30 pc^2 by means of the NeIII 15.6 mum/NeII 12.8 mum and NIII 57 mum/NII 122 mum line ratios. The electron densities (n_e) derived from the OIII lines ratio indicate the presence of diffuse ionized material with n_e of \~10^{1.8-2.6} cm^{-3}. The NIII/NII ratio show two clear gradients, one pointing toward the Quintuplet cluster and the other pointing toward the Arches cluster. The model used to explain the ionization structure shows that the large scale ionization of the whole region can be accounted for by the UV radiation produced by the Quintuplet and the Arches cluster. Any other ionization mechanism should play a minor role. We also investigate the influence of the clusters on the bubble of warm dust seen in the MSX infrared images. The warm dust is well correlated with the ionized gas indicating that the dust is also heated by the radiation from both clusters. Furthermore, the elliptical rather than circular symmetry of some structures like the Thermal Filaments can also be explained when one considers the combined effects of both the Arches and the Quintuplet clusters. The bubble is filled with continuum emission of hard X rays and with emision from the 6.4 keV line of neutral or low ionized Fe.