High-energy radiation from collisions of high velocity clouds and the Galactic disk

Abstract

High-velocity clouds (HVCs) are interstellar clouds of atomic hydrogen that do not partake of the Galactic rotation and have velocities of a several hundred kilometers per second. A considerable number of these clouds are falling down towards the Galactic disk. HVCs form large and massive complexes, so their collisions with the disk must release a great amount of energy into the interstellar medium. The cloud-disk interaction produces two shocks, one propagates through the cloud and the other through the disk; the properties of these shocks depend mainly on the cloud velocity and the disk-cloud density ratio. In this work we study the conditions necessary for these shocks to accelerate particles by diffusive shock acceleration and the produced non-thermal radiation. We analyze particle acceleration in both the cloud and disk shocks. Solving a time-dependent 2-D transport equation for both relativistic electrons and protons we obtain particle distributions and non-thermal spectral energy distributions. In a shocked cloud significant synchrotron radio emission is produced along with soft gamma rays. In the case of acceleration in the shocked disk, the non-thermal radiation is stronger; the gamma rays, of leptonic origin, might be detectable with current instruments. A large number of protons are injected into the Galactic interstellar medium, and locally exceed the cosmic-ray background. We conclude that under adequate conditions the contribution from HVC-disk collisions to the galactic population of relativistic particles and the associated extended non-thermal radiation might be important.

12 pages, 11 figures; accepted for publication in MNRAS

References in corpus (12)

• The major upgrade of the MAGIC telescopes, Part II: A performance study using observations of the Crab Nebula
• A Magnetized Jet from a Massive Protostar
• Distances to Galactic high-velocity clouds. I. Cohen Stream, complex GCP, cloud g1
• Smith's Cloud: A High-velocity Cloud Colliding with the Milky Way
• Gamma-ray novae as probes of relativistic particle acceleration at non-relativistic shocks
• Mechanism for spectral break in cosmic ray proton spectrum from Supernova remnant W44
• Modeling Bright Gamma-ray and Radio Emission at Fast Cloud Shocks
• Fermi-LAT Observations of High- and Intermediate-Velocity Clouds: Tracing Cosmic Rays in the Halo of the Milky Way
• Investigating Particle Acceleration in Protostellar Jets: The Triple Radio Continuum Source in Serpens
• The Smith Cloud and its dark matter halo: Survival of a Galactic disc passage
• Collisions between Dark Matter Confined High Velocity Clouds and Magnetized Galactic Disks: The Smith Cloud
• Runaway stars as cosmic ray injectors inside molecular clouds

Cited by in corpus (8)

• Non-thermal emission from stellar bow shocks
• High-energy processes in starburst-driven winds
• Radiation from the impact of broad-line region clouds onto AGN accretion disks
• Super-Accreting Active Galactic Nuclei as Neutrino Sources
• Estimating the Fuel Supply Rate on the Galactic Disk from High Velocity Clouds (HVCs) Infall
• Radio polarization from runaway star bowshocks-I. The general case
• Gamma rays from reaccelerated cosmic rays in high velocity clouds colliding with the Galactic disk
• Non-thermal emission from fall-back clouds in the Broad-Line Region of Active Galactic Nuclei