NH3 in the Central 10 pc of the Galaxy. II. Determination of Opacity for Gas with Large Linewidths

Abstract

The 23 GHz emission lines from the NH3 rotation inversion transitions are widely used to investigate the kinematics and physical conditions in dense molecular clouds. The line profile is composed of hyperfine components which can be used to calculate the opacity of the gas (Ho & Townes 1983). If the intrinsic linewidth of the gas exceeds one half of the separation of these quadrupole hyperfine components (~5-10 km/s) these lines blend together and the observed linewidths greatly overestimate the intrinsic linewidths. If uncorrected, these artificially broad linewidths will lead to artificially high opacities. We have observed this effect in our NH3 data from the central 10 pc of the Galaxy where uncorrected NH3 (1,1) linewidths of ~30 km/s exaggerate the intrinsic linewidths by more than a factor of two (Genzel & Townes 1987). Models of the effect of blending on the line profile enable us to solve for the intrinsic linewidth and opacity of NH3 using the observed linewidth and intensity of two NH3 rotation inversion transitions. We present the result of the application of this method to our Galactic Center data. We successfully recover the intrinsic linewidth and opacity of the gas. Clouds close to the nucleus in projected distance as well as those that are being impacted by Sgr A East show the highest intrinsic linewidths. The cores of the ``southern streamer'' (Ho et al. 1991; Coil & Ho 1999, 2000) and the ``50 km/s'' giant molecular cloud have the highest opacities.

27 pages, 10 figures, accepted for publication in ApJ

References in corpus (1)

• NH3 in the Central 10 pc of the Galaxy I: General Morphology and Kinematic Connections Between the CND and GMCs

Cited by in corpus (11)

• The Nature of the Molecular Environment within 5 pc of the Galactic Center
• Three-Dimensional Observations of H_2 Emission around Sgr A East - I. Structure in the Central 10 Parsecs of Our Galaxy
• Dense Gas in Nearby Galaxies: XVII. The Distribution of Ammonia in NGC253, Maffei2 and IC342
• Star Formation and Dynamics in the Galactic Centre
• A Complete Survey of the Central Molecular Zone in NH3
• Higgs-induced spectroscopic shifts near strong gravity sources
• The Fossil Nuclear Outflow in the Central 30 pc of the Galactic Center
• Ammonia mapping observations toward the Galactic massive star-forming region Sh 2-255 and Sh 2-257
• A Multi-Line Ammonia Survey of the Galactic Center Region with the Tsukuba 32-m Telescope - I. Observations and Data
• Hot Molecular Gas in the Central 10 Parsecs of the Galaxy
• Ammonia mapping observations of the Galactic infrared bubble N49: Three NH${}_3$ clumps along the molecular filament