摘要：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-H2CO transitions at 218 GHz and 291 GHz towards seven
Galactic center clouds. From the temperature-sensitive integrated intensity line ratios of
H2CO(32,1 −22,0)/H2CO(30,3 −20,2) and H2CO(42,2 −32,1)/H2CO(40,4 −30,3) in combination with radiative transfer models, we
produce gas temperature maps of our targets. These transitions are sensitive to gas with
densities of ~105 cm-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
H2CO(40,4 −30,3)/H2CO(30,3 −20,2), we constrain the density of this warm gas to
104
−106 cm-3. We find a positive correlation between the line width
of the main H2CO
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 = 105
cm-3.
关键词：Galaxy: center;ISM: molecules;ISM: structure;ISM: clouds;submillimeter: ISM
