Dense gas in the Galactic central molecular zone is warm and heated by turbulence
Journal article, 2016
Context. The Galactic center is the closest region where we can study star formation under extreme physical conditions like those in high-redshift galaxies. Aims. We measure the temperature of the dense gas in the central molecular zone (CMZ) and examine what drives it. Methods. We mapped the inner 300 pc of the CMZ in the temperature-sensitive J = 3-2 para-formaldehyde (p-H2CO) transitions. We used the 3(2,1)-2(2,0)/3(0,3)-2(0,2) line ratio to determine the gas temperature in n similar to 10(4) - 10(5) cm(-3) gas. We have produced temperature maps and cubes with 30 0 0 and 1 km s(-1) resolution and published all data in FITS form. Results. Dense gas temperatures in the Galactic center range from similar to 60 K to > 100 K in selected regions. The highest gas temperatures T-G > 100 K are observed around the Sgr B2 cores, in the extended Sgr B2 cloud, the 20 km s(-1) and 50 km s(-1) clouds, and in "The Brick" (G0.253 + 0.016). We infer an upper limit on the cosmic ray ionization rate zeta(CR) < 10(-14) s(-1). Conclusions. The dense molecular gas temperature of the region around our Galactic center is similar to values found in the central regions of other galaxies, in particular starburst systems. The gas temperature is uniformly higher than the dust temperature, confirming that dust is a coolant in the dense gas. Turbulent heating can readily explain the observed temperatures given the observed line widths. Cosmic rays cannot explain the observed variation in gas temperatures, so CMZ dense gas temperatures are not dominated by cosmic ray heating. The gas temperatures previously observed to be high in the inner similar to 75 pc are confirmed to be high in the entire CMZ.
cosmic rays
ISM: structure
ISM: clouds
Galaxy: nucleus
Galaxy: center
ISM: molecules
Author
A. Ginsburg
European Southern Observatory (ESO)
C. Henkel
King Abdulaziz University
Max Planck Society
Y. Ao
National Astronomical Observatory of Japan
Chinese Academy of Sciences
D. Riquelme
Max Planck Society
J. K. F. Mann
Max Planck Society
T. Pillai
Max Planck Society
E. A. C. Mills
National Radio Astronomy Observatory
M. A. Requena-Torres
Max Planck Society
K. Immer
European Southern Observatory (ESO)
L. Testi
European Southern Observatory (ESO)
J. Ott
National Radio Astronomy Observatory
J. Bally
University of Colorado
C. Battersby
Harvard-Smithsonian Center for Astrophysics
J. Darling
University of Colorado
Susanne Aalto
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
T. Stanke
European Southern Observatory (ESO)
S. Kendrew
University of Oxford
J. M. D. Kruijssen
Max Planck Society
S. Longmore
Liverpool John Moores University
J. Dale
Ludwig Maximilian University of Munich (LMU)
R. Guesten
Max Planck Society
K. M. Menten
Max Planck Society
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 586 Art nr A50- A50Subject Categories (SSIF 2011)
Astronomy, Astrophysics and Cosmology
DOI
10.1051/0004-6361/201526100