Result: 74 MHz Nonthermal Emission from Molecular Clouds: Evidence for a Cosmic Ray Dominated Region at the Galactic Center

Title:
74 MHz Nonthermal Emission from Molecular Clouds: Evidence for a Cosmic Ray Dominated Region at the Galactic Center
Authors:
YUSEF-ZADEH, F, WARDTE, M, LIS, D, VITI, S, BROGAN, C, CHAMBERS, E, POUND, M, RICKERT, M
Source:
The journal of physical chemistry. A. 117(39):9404-9419
Publisher Information:
Washington, DC: American Chemical Society, 2013.
Publication Year:
2013
Physical Description:
print, 64 ref
Original Material:
INIST-CNRS
Subject Terms:
General chemistry, physical chemistry, Chimie générale, chimie physique, Materials, Matériaux, Atomic molecular physics, Physique atomique et moléculaire, Sciences exactes et technologie, Exact sciences and technology, Sciences appliquees, Applied sciences, Electronique, Electronics, Electronique des semiconducteurs. Microélectronique. Optoélectronique. Dispositifs à l'état solide, Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices, Dispositifs magnétoélectriques, magnétostrictifs, magnétoacoustiques, magnétooptiques et magnétothermiques. Electronique de spin, Magnetoelectric, magnetostrictive, magnetoacoustic, magnetooptic and magnetothermal devices. Spintronics, Terre, ocean, espace, Earth, ocean, space, Astronomie, Astronomy, Systèmes stellaires. Objets et systèmes galactiques et extragalactiques. L'univers, Stellar systems. Galactic and extragalactic objects and systems. The universe, Divers, Other topics on stellar systems; galactic and extragalactic objects and systems; the universe, Composé minéral, Inorganic compounds, Continuum, Continuo, Emission rayonnement, Radiation emission, Emisión radiación, Haute température, High temperature, Alta temperatura, Hydrogène Molécule, Hydrogen Molecules, Ionisation, Ionization, Molécule d'hydrogène, Hydrogen molecules, Molécule diatomique, Diatomic molecules, Molécule interstellaire, Interstellar molecules, Nuage moléculaire, Molecular clouds, Rayonnement cosmique, Cosmic radiation, Rayonnement synchrotron, Synchrotron radiation, Réduction donnée, Data reduction, Technique diagnostic, Diagnostic techniques, Fe, H2
Time:
8575, 9838
Document Type:
Academic journal Article
File Description:
text
Language:
English
Author Affiliations:
Department of Physics and Astronomy and Center for Interdisciplinary Research in Astronomy, Northwestern University, Evanston, Illinois 60208, United States
Department of Physics & Astronomy and Research Centre for Astronomy, Astrophysics & Astrophotonics, Macquarie University, Sydney, NSW 2109, Australia
California Institute of Technology, MC 320-47, Pasadena, California 91125, United States
Department of Physics and Astronomy, University College London, Gower Street, London WCIE 6BT, United Kingdom
National Radio Astronomy Observatory, Charlottesville, Virginia 22903, United States
Physikalisches Institut, Universität zu Köln, Cologne 50397, Germany
Department of Astronomy, University of Maryland, College Park, Maryland 20742, United States
ISSN:
1089-5639
Access URL:
http://pascal-francis.inist.fr/vibad/index.php?action=search&terms=27894951
Rights:
Copyright 2015 INIST-CNRS
CC BY 4.0
Sauf mention contraire ci-dessus, le contenu de cette notice bibliographique peut être utilisé dans le cadre d’une licence CC BY 4.0 Inist-CNRS / Unless otherwise stated above, the content of this bibliographic record may be used under a CC BY 4.0 licence by Inist-CNRS / A menos que se haya señalado antes, el contenido de este registro bibliográfico puede ser utilizado al amparo de una licencia CC BY 4.0 Inist-CNRS
Notes:
Astronomy

Electronics
Accession Number:
edscal.27894951
Database:
PASCAL Archive

Further Information

We present 74 MHz radio continuum observations of the Galactic center region. These measurements show nonthermal radio emission arising from molecular clouds that is unaffected by free―free absorption along the line of sight. We focus on one cloud, G0.13-0.13, representative of the population of molecular clouds that are spatially correlated with steep spectrum (α74MHz327MHz = 1.3 ± 0.3) nonthermal emission from the Galactic center region. This cloud lies adjacent to the nonthermal radio filaments of the Arc near l ∼ 0.2° and is a strong source of 74 MHz continuum, SiO (2-1), and Fe I Kα 6.4 keV line emission. This three-way correlation provides the most compelling evidence yet that relativistic electrons, here traced by 74 MHz emission, are physically associated with the G0.13-0.13 molecular cloud and that low-energy cosmic ray electrons are responsible for the Fe I Kα line emission. The high cosmic ray ionization rate ∼10―13 s―1 H―1 is responsible for heating the molecular gas to high temperatures and allows the disturbed gas to maintain a high-velocity dispersion. Large velocity gradient (LVG) modeling of multitransition SiO observations of this cloud implies H2 densities ∼104―5 cm―3 and high temperatures. The lower limit to the temperature of G0.13-0.13 is ∼100 K, whereas the upper limit is as high as 1000 K. Lastly, we used a time-dependent chemical model in which cosmic rays drive the chemistry of the gas to investigate for molecular line diagnostics of cosmic ray heating. When the cloud reaches chemical equilibrium, the abundance ratios of HCN/HNC and N2H+/HCO+ are consistent with measured values. In addition, significant abundance of SiO is predicted in the cosmic ray dominated region of the Galactic center. We discuss different possibilities to account for the origin of widespread SiO emission detected from Galactic center molecular clouds.