Self-modulation of cosmic rays in molecular clouds: Imprints in the radio observations

Abstract

We analyze properties of non-thermal radio emission from the Central Molecular Zone (CMZ) and individual molecular clouds, and argue that the observed features can be interpreted in the framework of our recent theory of self-modulation of cosmic rays (CRs) penetrating dense molecular regions. For clouds with gas column densities of $\sim 10^{23}$ cm${}^{-2}$, the theory predicts depletion of sub-GeV CR electrons, occurring due to self-modulation of CR protons and leading to harder synchrotron spectra in the sub-GHz range. The predicted imprints of electron depletion in the synchrotron spectra agree well with the spectral hardening seen in available radio observations of the CMZ. A similar, but even stronger effect on the synchrotron emission is predicted for individual (denser) CMZ clouds, such as the Sgr B2. However, the emission at frequencies above $\sim$ GHz, where observational data are available, is completely dominated by the thermal component, and therefore new observations at lower frequencies are needed to verify the predictions.

arXiv commentAccepted for publication in ApJ

References in corpus (31)

• The Nuclear Bulge of the Galaxy. III. Large-Scale Physical Characteristics of Stars and Interstellar Matter
• Development of the Model of Galactic Interstellar Emission for Standard Point-Source Analysis of Fermi Large Area Telescope Data
• Investigating the Cosmic-Ray Ionization Rate in the Galactic Diffuse Interstellar Medium through Observations of H3+
• Turbulent molecular clouds
• 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
• Hot and Diffuse Clouds near the Galactic Center Probed by Metastable H3+
• A lower limit of 50 microgauss for the magnetic field near the Galactic Centre
• The physical and chemical structure of Sagittarius B2, I. Three-dimensional thermal dust and free-free continuum modeling on 100 au to 45 pc scales
• Interacting Cosmic Rays with Molecular Clouds: A Bremsstrahlung Origin of Diffuse High Energy Emission from the Inner 2deg by 1deg of the Galactic Center
• Interstellar dust charging in dense molecular clouds: cosmic ray effects
• Interstellar magnetic fields in the Galactic center region
• New very local interstellar spectra for electrons, positrons, protons and light cosmic ray nuclei
• The Central 300 pc of the Galaxy probed by infrared spectra of H${}_3^{+}$ and CO: part I. Predominance of warm and diffuse gas and high H${}_2$ ionization rate
• Cosmic-Ray Heating of Molecular Gas in the Nuclear Disk: Low Star Formation Efficiency
• Penetration of cosmic rays into dense molecular clouds: role of diffuse envelope
• The Dense Gas Fraction in Galactic Center Clouds
• Gamma rays as probes of cosmic-ray propagation and interactions in galaxies
• The physical and chemical structure of Sagittarius B2 -- V. Non-thermal emission in the envelope of Sgr B2
• Observational signatures of cosmic ray interactions in molecular clouds
• Gamma-Ray Emission from Molecular Clouds Generated by Penetrating Cosmic Rays
• Spectrum of Relativistic and Subrelativistic Cosmic Rays in the 100 pc Central Region
• Interpretation of radio continuum and molecular line observations of Sgr B2: free-free and synchrotron emission, and implications for cosmic rays
• Molecular Clouds as the Origin of the Fermi Gamma-Ray GeV-Excess
• The diffuse molecular component in the nuclear bulge of the Milky Way
• Australia Telescope Compact Array Radio Continuum 1384 and 2368 Mhz Observations of Sagittarius B
• Magnetic field generation in galactic molecular clouds
• Search for synchrotron emission from secondary leptons in dense cold starless cores
• The Milky Way's Central Molecular Zone
• An OH(1720 MHz) Maser and a Nonthermal Radio Source in Sgr B2(M): A SNR--Molecular Cloud Interaction Site?
• Prospects for Detection of Synchrotron Emission from Secondary Electrons and Positrons in Starless Cores: Application to G0.216+0.016

Cited by in corpus (1)

• Low energy cosmic rays