The cosmic-ray and gas content of the Cygnus region as measured in gamma rays by the Fermi Large Area Telescope

Abstract

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 gamma-ray energies. Several gamma-ray pulsars and other energetic sources are seen in this direction. In this paper we analyse the gamma-ray emission measured by the Fermi Large Area Telescope in the energy range from 100 MeV to 100 GeV in order to probe the gas and cosmic-ray content over the scale of the whole Cygnus complex. 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. The integral HI 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=N(H2)/W(CO) ratio is consistent with other LAT measurements in the Local Arm. We detect significant gamma-ray emission from dark neutral gas for a mass corresponding to ~40% of that traced by CO. 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. (abridged)

16 pages, 13 figures. Accepted for publication on A&A. Contact authors: I. A. Grenier ([email protected]) and L. Tibaldo ([email protected])

References in corpus (18)

• TEMPO2, a new pulsar timing package. I: Overview
• Measurement of the Cosmic Ray e+ plus e- spectrum from 20 GeV to 1 TeV with the Fermi Large Area Telescope
• The Spectrum of the Isotropic Diffuse Gamma-Ray Emission Derived From First-Year Fermi Large Area Telescope Data
• Planck Early Results: All sky temperature and dust optical depth from Planck and IRAS: Constraints on the "dark gas" in our galaxy
• Detection of 16 Gamma-Ray Pulsars Through Blind Frequency Searches Using the Fermi LAT
• Precise Gamma-Ray Timing and Radio Observations of 17 Fermi Gamma-Ray Pulsars
• Inverse Compton Origin of the Hard X-Ray and Soft Gamma-Ray Emission from the Galactic Ridge
• Discovery of TeV Gamma-Ray Emission from the Cygnus Region of the Galaxy
• Eight gamma-ray pulsars discovered in blind frequency searches of Fermi LAT data
• C${}^{+}$ detection of warm dark gas in diffuse clouds
• Constraints on the Cosmic-Ray Density Gradient beyond the Solar Circle from Fermi gamma-ray Observations of the Third Galactic Quadrant
• The Structure of Molecular Clouds: I - All Sky Near Infrared Extinction Maps
• Fermi Large Area Telescope Observations of the Cygnus Loop Supernova Remnant
• Gamma-rays from halos around stars and the Sun
• Pulsed Gamma-rays from PSR J2021+3651 with the Fermi Large Area Telescope
• Optimization of Moment Masking for CO Spectral Line Surveys
• PSR J2030+3641: radio discovery and gamma-ray study of a middle-aged pulsar in the now identified Fermi-LAT source 1FGL J2030.0+3641
• The Balloon-Borne Large Aperture Submillimeter Telescope (BLAST) 2005: A 10 deg^2 Survey of Star Formation in Cygnus X

Cited by in corpus (37)

• The CO-to-H2 Conversion Factor
• Fermi Large Area Telescope Second Source Catalog
• Development of the Model of Galactic Interstellar Emission for Standard Point-Source Analysis of Fermi Large Area Telescope Data
• The 1st Fermi Lat Supernova Remnant Catalog
• Tracing the total molecular gas in galaxies: [CII] and the CO-dark gas
• Identification of the TeV Gamma-ray Source ARGO J2031+4157 with the Cygnus Cocoon
• Study of the diffuse gamma-ray emission from the Galactic plane with ARGO-YBJ
• Cosmic rays, gas and dust in nearby anticentre clouds : I -- CO-to-H2 conversion factors and dust opacities
• On the radial distribution of Galactic cosmic rays
• Pulsar TeV Halos Explain the TeV Excess Observed by Milagro
• Spectrum and Morphology of the Two Brightest Milagro Sources in the Cygnus Region: MGRO J2019+37 and MGRO J2031+41
• Molecular Gas Properties and CO-to-H2 Conversion Factors in the Central Kiloparsec of NGC 3351
• The Physical Drivers and Observational Tracers of CO-to-H2 Conversion Factor Variations in Nearby Barred Galaxy Centers
• Gamma rays as probes of cosmic-ray propagation and interactions in galaxies
• Planck intermediate results. XXVIII. Interstellar gas and dust in the Chamaeleon clouds as seen by Fermi LAT and Planck
• Fermi LAT and WMAP observations of the supernova remnant HB 21
• Fermi-LAT upper limits on gamma-ray emission from colliding wind binaries
• SOFIA/FIFI-LS Full-disk [CII] Mapping and CO-dark Molecular Gas across the Nearby Spiral Galaxy NGC 6946
• Chemical evolution of giant molecular clouds in simulations of galaxies
• Investigating $\gamma$-ray halos around three HAWC bright sources in Fermi-LAT data
• The Structure of Dark Molecular Gas in the Galaxy -- II. Physical State of "CO-Dark" Gas in the Perseus Arm
• Gamma-Ray Puzzles in Cygnus X: Implications for High-Energy Neutrinos
• Multiple emission components in the Cygnus cocoon detected from Fermi-LAT observations
• Dissecting the Mid-Infrared Heart of M83 with JWST
• On the Contribution of "Fresh" Cosmic Rays to the Excesses of Secondary Particles
• Selected Topics in Cosmic Ray Physics
• CO Multi-line Imaging of Nearby Galaxies (COMING). XII. CO-to-H${}_2$ Conversion Factor and Dust-to-Gas Ratio
• Identifying Galactic Sources of High-Energy Neutrinos
• Suzaku Observation of the Fermi Cygnus Cocoon: Search for a Signature of Young Cosmic-Ray Electrons
• A tale of cosmic rays narrated in gamma rays by Fermi
• Probing the origin of cosmic rays in Cygnus Cocoon using ultrahigh-energy gamma-ray and neutrino observations
• Probing local cosmic rays using Fermi-LAT observation of a mid-latitude region in the third Galactic quadrant
• Limits on Leptonic TeV Emission from the Cygnus Cocoon with Swift-XRT
• High Latitude, Translucent Molecular Clouds as Probes of Local Cosmic Rays
• Interaction of escaping cosmic rays with molecular clouds
• Uncovering neutrinos from cosmic ray factories: the Multi Point Source method
• Effects of self-generated turbulence on Galactic Cosmic Ray propagation and associated diffuse gamma-ray emission