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.

Accepted for publication in ApJ

References in corpus (12)

• Spatial distribution of interstellar gas in the innermost 3 kpc of our Galaxy
• 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
• Gamma rays as probes of cosmic-ray propagation and interactions in galaxies
• Observational signatures of cosmic ray interactions in molecular clouds
• 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
• Australia Telescope Compact Array Radio Continuum 1384 and 2368 Mhz Observations of Sagittarius B
• The Milky Way's Central Molecular Zone
• Search for synchrotron emission from secondary leptons in dense cold starless cores
• 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