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Regularized 3D spectroscopy with CubeFit: method and application to the Galactic Center Circumnuclear disk

The Galactic Center black hole and the nuclear star cluster are surrounded by a clumpy ring of gas and dust (the circumnuclear disk, CND) that rotates about them at a standoff distance of ~1.5 pc. The mass and density of individual clumps in the CND are disputed. We seek to use H$_2$ to characterize the clump size distribution and to investigate the morphology and dynamics of the interface between the ionized interior layer of the CND and the molecular reservoir lying further out (corresponding to the inner rim of the CND, illuminated in ultraviolet light by the central star cluster). We have observed two fields of approximately 20"x20" in the CND at near-infrared wavelengths with the OSIRIS spectro-imager at the Keck Observatory. These two fields, located at the approaching and receding nodes of the CND, best display this interface. Our data cover two H$_2$ lines as well as the Br$γ$ line (tracing H ii). We have developed the tool CubeFit, an original method to extract maps of continuous physical parameters (such as velocity field and velocity dispersion) from integral-field spectroscopy data, using regularization to largely preserve spatial resolution in regions of low signal-to-noise ratio. This original method enables us to isolate compact, bright features in the interstellar medium of the CND. Several clumps in the southwestern field assume the appearance of filaments, many of which are parallel to each other. We conclude that these clumps cannot be self-gravitating.