The thermal state of molecular clouds in the Galactic center: evidence for non-photon-driven heating
Artikel i vetenskaplig tidskrift, 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-institutet

Chinese Academy of Sciences

C. Henkel

King Abdulaziz University

Max Planck-institutet

K. M. Menten

Max Planck-institutet

M. A. Requena-Torres

Max Planck-institutet

T. Stanke

European Southern Observatory (ESO)

R. Mauersberger

Atacama Large Millimeter-submillimeter Array (ALMA)

Susanne Aalto

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

S. Muhle

Universität Bonn

J. G. Mangum

National Radio Astronomy Observatory

Astronomy and Astrophysics

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

Vol. 550 A135


Astronomi, astrofysik och kosmologi



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