Temperature structures in Galactic center clouds Direct evidence for gas heating via turbulence

• Published in: Astronomy and astrophysics (Berlin) Vol. 595; p. A94
• Main Authors: Immer, K, Kauffmann, J, Pillai, T, Ginsburg, A, Menten, K M
• Format: Journal Article
• Language: English
• Published: 01.11.2016
• Subjects: Clouds; Density; Gas heating; Gas temperature; Heating; Molecular structure; Turbulence; Turbulent flow
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361/201628777

The central molecular zone at the center of our Galaxy is the best template to study star formation processes under extreme conditions, similar to those in high-redshift galaxies. We observed on-the-fly maps of para-H sub(2) CO transitions at 218 GHz and 291 GHz towards seven Galactic center clouds. From the temperature-sensitive integrated intensity line ratios of H sub(2) CO(3 sub(2,1)-2 sub(2,0))/ H sub(2) CO(3 sub(0,3)-2 sub(0,2)) and H sub(2) CO(4 sub(2,2)-3 sub(2,1))/ H sub(2) CO(4 sub(0,4)-3 sub(0,3)) in combination with radiative transfer models, we produce gas temperature maps of our targets. These transitions are sensitive to gas with densities of ~10 super(5) cm super(-3) and temperatures <150 K. The measured gas temperatures in our sources are all higher (>40 K) than their dust temperatures (~25 K). Our targets have a complex velocity structure that requires a careful disentanglement of the different components. We produce temperature maps for each of the velocity components and show that the temperatures of the components differ, revealing temperature gradients in the clouds. Combining the temperature measurements with the integrated intensity line ratio of H sub(2) CO(4 sub(0,4)-3 sub(0,3))/ H sub(2) CO(3 sub(0,3)-2 sub(0,2)), we constrain the density of this warm gas to 10 super(4)-10 super(6) cm super(-3). We find a positive correlation between the line width of the main H sub(2) CO lines and the temperature of the gas, direct evidence for gas heating via turbulence. Our data is consistent with a turbulence heating model with a density of n= 10 super(5) cm super(-3).