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The Cosmic-Ray and Gas Content of the Cygnus Region as Measured in Gamma Rays by the Fermi Large Area TelescopeContext. The Cygnus region hosts a giant molecular-cloud complex which actively forms massive stars. Interactions of cosmic rays with interstellar gas and radiation fields make it shine at y-ray energies. Several gamma-ray pulsars and other energetic sources are seen in this direction. Aims. In this paper we analyse the gamma-ray emission measured by the Fermi Large Area Telescope in the energy range from 100 Me V to 100 Ge V in order to probe the gas and cosmic-ray content over the scale of the whole Cygnus complex. The gamma-ray emission on the scale of the central massive stellar clusters and from individual sources is addressed elsewhere. Methods. The signal from bright pulsars is largely reduced by selecting photons in their off-pulse phase intervals. We compare the diffuse gamma-ray emission with interstellar gas maps derived from radio/mm-wave lines and visual extinction data. and a global model of the region, including other pulsars and gamma-ray sources, is sought. Results. The integral H I emissivity above 100 MeV averaged over the whole Cygnus complex amounts to 12.06 +/- 0.11 (stat.) (+0.15 -0.84) (syst.J] x 10(exp -26) photons /s / sr / H-atom, where the systematic error is dominated by the uncertainty on the H I opacity to calculate its column densities. The integral emissivity and its spectral energy distribution are both consistent within the systematics with LAT measurements in the interstellar space near the solar system. The average X(sub co) N(H2)/W(sub co) ratio is found to be [1.68 +/- 0.05 (stat.) (H I opacity)] x 1020 molecules cm-2 (K km/s /r, consistent with other LAT measurements in the Local Arm. We detect significant gamma-ray emission from dark neutral gas for a mass corresponding to approx 40% of that traced by CO. The total interstellar mass in the Cygnus complex inferred from its gamma-ray emission amounts to 8(+5 -1) x 10(exp 6) Solar M at a distance of 1.4 kpc. Conclusions. Despite the conspicuous star formation activity and large masses of the interstellar clouds, the cosmic-ray population in the Cygnus complex averaged over a few hundred parsecs is similar to that of the local interstellar space.
Document ID
20120008358
Acquisition Source
Goddard Space Flight Center
Document Type
Preprint (Draft being sent to journal)
Authors
Ackermann, M. (Kavli Inst. for Particle Astrophysics and Cosmology Stanford, CA, United States)
Ajello, M. (Kavli Inst. for Particle Astrophysics and Cosmology Stanford, CA, United States)
Allafort, A. (Kavli Inst. for Particle Astrophysics and Cosmology Stanford, CA, United States)
Baldini, L. (Istituto Nazionale di Fisica Nucleare Pisa, Italy)
Ballet, J. (Paris VII Univ. France)
Barbiellini, G. (Istituto Nazionale di Fisica Nucleare Trieste, Italy)
Bastieri, D. (Istituto Nazionale di Fisica Nucleare Padova, Italy)
Belfiore, A. (Istituto di Astrofisica Spaziale e Fisica Cosmica (INAF-IASF) Milano, Italy)
Bellazzini, R. (Istituto Nazionale di Fisica Nucleare Pisa, Italy)
Berenji, B. (Kavli Inst. for Particle Astrophysics and Cosmology Stanford, CA, United States)
Blandford, R. D. (Kavli Inst. for Particle Astrophysics and Cosmology Stanford, CA, United States)
Bloom, E. D. (Kavli Inst. for Particle Astrophysics and Cosmology Stanford, CA, United States)
Bonamente, E. (Istituto Nazionale di Fisica Nucleare Perugia, Italy)
Borgland, A. W. (Kavli Inst. for Particle Astrophysics and Cosmology Stanford, CA, United States)
Bottacini, E. (Kavli Inst. for Particle Astrophysics and Cosmology Stanford, CA, United States)
Bregeon, J. (Istituto Nazionale di Fisica Nucleare Pisa, Italy)
Brigida, M. (Politecnico di Bari Bari, Italy)
Bruel, P. (Ecole Polytechnique Palaiseau, France)
Buehler, R. (Kavli Inst. for Particle Astrophysics and Cosmology Stanford, CA, United States)
Buson, S. (Istituto Nazionale di Fisica Nucleare Padova, Italy)
Caliandro, G. A. (Campus UAB Barcelona, Spain)
Harding, A. K. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Hays, E. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Thompson, D. J. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Troja, E. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Date Acquired
August 25, 2013
Publication Date
October 28, 2011
Subject Category
Astronomy
Report/Patent Number
GSFC.JA.6883.2012
GSFC.JA.5859.2012
Distribution Limits
Public
Copyright
Public Use Permitted.

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