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

LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, Univ. Paris Diderot, UPMC Univ. Paris 06, Sorbonne Paris Cité, 5 place Jules Janssen, 92195 Meudon, France
e-mail: anna.ciurlo@obspm.fr; thibaut.paumard@obspm.fr; daniel.rouan@obspm.fr

Received: 12 August 2015
Accepted: 21 April 2016

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″ × 29″, with a spectral resolution R = 1300 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.