Hot molecular hydrogen in the central parsec of the Galaxy through near-infrared 3D fitting

Abstract

Aims. We have investigated neutral gas in the central cavity of the circumnuclear disk (CND) at the Galactic Center, where the ionized minispiral lies, to describe the H2 distribution and properties in this ionized environment. Methods. This study was carried out through a spectro-imaging data cube of the central cavity obtained with SPIFFI on the VLT. The observed field of view is 36"x 29" , with a spectral resolution R = 1 300 in the near-infrared. These observations cover several H2 lines. To preserve the spatial resolution and avoid edge effects, we applied a new line-fitting method that consists of a regularized 3D fitting. We also applied a more classical 1D fitting to compare the relative strength of the H2 lines. Results. We present high spatial and spectral resolution maps of the intensity, velocity, and width of five H2 lines and an extinction map derived from H2. Molecular gas is detected everywhere in the field. In particular, in addition to the known CND features, we detected an emission from the northern arm cloud and from the minicavity. The excitation diagrams allow us to estimate the temperature, mass, and density of these features. Conclusions. We interpret the CND emission as coming from a hot, thermalized, thin layer at the surface of the clouds. The observed H2 corresponds only to a small fraction of the total H2 mass. The emission remains fairly strong in the whole central cavity, but it is not thermalized. A strong deviation from thermal equilibrium is detected near the minicavity. We suggest that this emission is caused by constantly forming H2 that is destroyed again before it reaches ortho/para equilibrium.

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