GREAT confirms transient nature of the circumnuclear disk

Abstract

We report SOFIA/GREAT, Herschel/HIFI, and ground-based velocity-resolved spectroscopy of carbon monoxide (CO) rotational transitions from J=2-1 to J=16-15 toward two positions in the circum-nuclear disk (CND) in our Galactic center. Radiative transfer models were used to derive information on the physical state of the gas traced by CO. The excitation of the CO gas cannot be explained by a single physical component, but is clearly the superposition of various warm gas phases. In a two-component approach, our large velocity gradient (LVG) analysis suggests high temperatures of ~200 K with moderate gas densities of only ~10^4.5 cm^-3 for the bulk of the material. A higher excited phase, carrying ~20-30% of the column densities, is warmer (~300-500 K) but only slightly denser ~10^5.3 cm^-3. These densities are too low to self-stabilize the clumps against their high internal turbulence and fall below the Roche density (>10^7 cm^-3) at 1.5 pc galactocentric distance. We conclude that the bulk of the material in the CND is not organized by self-gravity nor stable against tidal disruption, and must be transient.

Accepted in A&A special issue for SOFIA/GREAT

References in corpus (7)

• GREAT: the SOFIA high-frequency heterodyne instrument
• High-resolution wide-band Fast Fourier Transform spectrometers
• Highly-excited CO emission in APM08279+5255 at z=3.9
• Vibrationally Excited HCN in the Luminous Infrared Galaxy NGC 4418
• GREAT/SOFIA atmospheric calibration
• Surviving the hole I: Spatially resolved chemistry around Sgr A*
• The Galactic Centre in the Far Infrared

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