The thermal state of molecular clouds in the Galactic center: evidence for non-photon-driven heating
Journal article, 2013

We used the Atacama Pathfinder Experiment (APEX) 12 m telescope to observe the J(KAKc) = 3(03) -> 2(02), 3(22) -> 2(21), and 3(21) -> 2(20) transitions of para-H2CO at 218 GHz simultaneously to determine kinetic temperatures of the dense gas in the central molecular zone (CMZ) of our Galaxy. The map extends over approximately 40' x 8' (similar to 100 x 20 pc(2)) along the Galactic plane with a linear resolution of 1.2 pc. The strongest of the three lines, the H2CO (3(03) -> 2(02)) transition, is found to be widespread, and its emission shows a spatial distribution similar to ammonia. The relative abundance of para-H2CO is 0.5 - 1.2 x 10(-9), which is consistent with results from lower frequency H2CO absorption lines. Derived gas kinetic temperatures for individual molecular clouds range from 50K to values in excess of 100 K. While a systematic trend toward (decreasing) kinetic temperature versus (increasing) angular distance from the Galactic center (GC) is not found, the clouds with highest temperature (T-kin > 100 K) are all located near the nucleus. For the molecular gas outside the dense clouds, the average kinetic temperature is 65 +/- 10 K. The high temperatures of molecular clouds on large scales in the GC region may be driven by turbulent energy dissipation and / or cosmic-rays instead of photons. Such a non-photon-driven thermal state of the molecular gas provides an excellent template for the more distant vigorous starbursts found in ultraluminous infrared galaxies (ULIRGs).


Y. Ao

Max Planck Society

Chinese Academy of Sciences

C. Henkel

King Abdulaziz University

Max Planck Society

K. M. Menten

Max Planck Society

M. A. Requena-Torres

Max Planck Society

T. Stanke

European Southern Observatory (ESO)

R. Mauersberger

Atacama Large Millimeter-submillimeter Array (ALMA)

Susanne Aalto

Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics

S. Muhle

University of Bonn

J. G. Mangum

National Radio Astronomy Observatory

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 550 A135

Subject Categories

Astronomy, Astrophysics and Cosmology



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