Gamma-Ray Emission from Molecular Clouds Generated by Penetrating Cosmic Rays

Abstract

We analyze the processes governing cosmic-ray (CR) penetration into molecular clouds and the resulting generation of gamma-ray emission. The density of CRs inside a cloud is depleted at lower energies due to the self-excited MHD turbulence. The depletion depends on the effective gas column density ("size") of the cloud. We consider two different environments where the depletion effect is expected to be observed. For the Central Molecular Zone, the expected range of CR energy depletion is $E\lesssim 10$ GeV, leading to the depletion of gamma-ray flux below $E_{\gamma }\approx 2$ GeV. This effect can be important for the interpretation of the GeV gamma-ray excess in the Galactic Center, which has been revealed from the standard model of CR propagation (assuming the CR spectrum inside a cloud to be equal to the interstellar spectrum). Furthermore, recent observations of some local molecular clouds suggest the depletion of the gamma-ray emission, indicating possible self-modulation of the penetrating low-energy CRs.

arXiv comment10 pages, 5 figures, accepted for publication in ApJ

References in corpus (66)

• The Structure of Cold Dark Matter Halos
• HEALPix -- a Framework for High Resolution Discretization, and Fast Analysis of Data Distributed on the Sphere
• Giant Gamma-ray Bubbles from Fermi-LAT: AGN Activity or Bipolar Galactic Wind?
• Dark Matter Annihilation in The Galactic Center As Seen by the Fermi Gamma Ray Space Telescope
• Fermi-LAT Observations of the Diffuse Gamma-Ray Emission: Implications for Cosmic Rays and the Interstellar Medium
• Diffuse Galactic continuum gamma rays. A model compatible with EGRET data and cosmic-ray measurements
• The Characterization of the Gamma-Ray Signal from the Central Milky Way: A Compelling Case for Annihilating Dark Matter
• Acceleration of petaelectronvolt protons in the Galactic Centre
• Detection of a Gamma-Ray Source in the Galactic Center Consistent with Extended Emission from Dark Matter Annihilation and Concentrated Astrophysical Emission
• The Nuclear Bulge of the Galaxy. III. Large-Scale Physical Characteristics of Stars and Interstellar Matter
• Background model systematics for the Fermi GeV excess
• Dark Matter and Pulsar Model Constraints from Galactic Center Fermi-LAT Gamma Ray Observations
• Development of the Model of Galactic Interstellar Emission for Standard Point-Source Analysis of Fermi Large Area Telescope Data
• The Fermi Galactic Center GeV Excess and Implications for Dark Matter
• Fermi-LAT Observations of High-Energy Gamma-Ray Emission Toward the Galactic Center
• Parametrization of gamma-ray production cross-sections for pp interactions in a broad proton energy range from the kinematic threshold to PeV energies
• The Spectrum and Morphology of the Fermi Bubbles
• GALPROP WebRun: an internet-based service for calculating galactic cosmic ray propagation and associated photon emissions
• Science with e-ASTROGAM (A space mission for MeV-GeV gamma-ray astrophysics)
• The Fermi Bubbles: Giant, Multi-Billion-Year-Old Reservoirs of Galactic Center Cosmic Rays
• Dense gas in the Galactic central molecular zone is warm and heated by turbulence
• Spatial distribution of interstellar gas in the innermost 3 kpc of our Galaxy
• Possible Evidence For Dark Matter Annihilation In The Inner Milky Way From The Fermi Gamma Ray Space Telescope
• Hot and Diffuse Clouds near the Galactic Center Probed by Metastable H3+
• Cosmic-ray ionisation in circumstellar discs
• CRDB: a database of charged cosmic rays
• Dark Matter Evidence, Particle Physics Candidates and Detection Methods
• GeV excess in the Milky Way: The Role of Diffuse Galactic gamma ray Emission template
• Gamma-ray Emission from Crushed Clouds in Supernova Remnants
• Gamma rays from molecular clouds
• Protostars: Forges of cosmic rays?
• Gamma-ray sky points to radial gradients in cosmic-ray transport
• Wild at Heart:-The Particle Astrophysics of the Galactic Centre
• Origin of the Fermi Bubble
• Cosmic-ray ionisation in collapsing clouds
• Planck intermediate results. XXI. Comparison of polarized thermal emission from Galactic dust at 353 GHz with interstellar polarization in the visible
• Physical conditions in the central molecular zone inferred by H3+
• Cosmic rays, gas and dust in nearby anticentre clouds : I -- CO-to-H2 conversion factors and dust opacities
• Fermi LAT study of cosmic-rays and the interstellar medium in nearby molecular clouds
• The Interaction of Cosmic Rays with Diffuse Clouds
• Probing Cosmic Rays in Nearby Giant Molecular Clouds with the Fermi Large Area Telescope
• Penetration of cosmic rays into dense molecular clouds: role of diffuse envelope
• Cosmic ray penetration in diffuse clouds
• Galactic Center Excess in Gamma Rays from Annihilation of Self-Interacting Dark Matter
• Cosmic ray spectrum in the local Galaxy
• The Galactic Center Molecular Cloud Survey. II. A Lack of Dense Gas & Cloud Evolution along Galactic Center Orbits
• Millisecond Pulsars, TeV Halos, and Implications For The Galactic Center Gamma-Ray Excess
• Improved Cosmic-Ray Injection Models and the Galactic Center Gamma-Ray Excess
• What causes the ionization rates observed in molecular clouds? The role of cosmic ray protons and electrons
• Unveiling the Origin of the Fermi Bubbles
• SUSY Implications from WIMP Annihilation into Scalars at the Galactic Centre
• Galactic Binaries Can Explain the Fermi Galactic Center Excess and 511 keV Emission
• Disrupted Globular Clusters and the Gamma-Ray Excess in the Galactic Centre
• Gamma-ray and X-ray emission from the Galactic Centre: hints on the nuclear star cluster formation history
• Fermi-LAT observations of the Sagittarius B complex
• Magnetic Mirroring and Focusing of Cosmic Rays
• Probing the Southern Fermi Bubble in Ultraviolet Absorption using Distant AGNs
• Spectrum of Relativistic and Subrelativistic Cosmic Rays in the 100 pc Central Region
• Leptonic origin of the 100 MeV gamma-ray emission from the Galactic Centre
• Molecular Clouds as the Origin of the Fermi Gamma-Ray GeV-Excess
• The diffuse molecular component in the nuclear bulge of the Milky Way
• On the GeV excess in the diffuse γ-ray emission towards the Galactic Center
• Parametrization of the nucleus-nucleus gamma-ray production cross sections below 100 GeV/nucleon: Subthreshold pions and Hard photons
• Local interstellar cosmic-ray spectra derived from gamma-ray emissivities
• The Galactic Isotropic $\gamma$-ray Background and Implications for Dark Matter
• Origin of X-ray and gamma-ray emission from the Galactic central region

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• Cosmic Ray Transport, Energy Loss, and Influence in the Multiphase Interstellar Medium
• Diffusive Versus Free-Streaming Cosmic Ray Transport in Molecular Clouds
• Observational signatures of cosmic ray interactions in molecular clouds
• Effective Shielding of $\lesssim$ 10 GeV Cosmic Rays from Dense Molecular Clumps
• Formation of the cosmic-ray halo: The role of nonlinear Landau damping
• Intrusion of MeV-TeV Cosmic-Rays into Molecular Clouds Studied by Ionization, the Neutral Iron Line, and Gamma-Rays
• The extragalactic $\gamma$-ray background: imprints from the physical properties and evolution of star-forming galaxy populations
• Self-modulation of cosmic rays in molecular clouds: Imprints in the radio observations
• Nuclear de-excitation line emissions from giant molecular clouds
• A GeV-TeV particle component and the barrier of cosmic-ray sea in the Central Molecular Zone
• On a possible origin of the gamma-ray excess around the Galactic Center
• High Energy Emission from the Galactic Center