36 research outputs found
On cosmic-ray production efficiency at supernova remnant shocks propagating into realistic diffuse interstellar medium
Using three-dimensional magnetohydrodynamics simulations, we show that the
efficiency of cosmic-ray (CR) production at supernova remnants (SNRs) is
over-predicted if it could be estimated based on proper motion measurements of
H filaments in combination with shock-jump conditions. Density
fluctuations of upstream medium make shock waves rippled and oblique almost
everywhere. The kinetic energy of the shock wave is transferred into that of
downstream turbulence as well as thermal energy which is related to the shock
velocity component normal to the shock surface. Our synthetic observation shows
that the CR acceleration efficiency as estimated from a lower downstream plasma
temperature, is overestimated by 10-40%, because rippled shock does not
immediately dissipate all upstream kinetic energy.Comment: 7 pages, 3 figures, 1 table, accepted for publication in ApJ; the
paper with full resolution images is
http://www.phys.aoyama.ac.jp/~ryo/papers/shimoda2015.pd
The History of The Milky Way: The Evolution of Star Formation, Cosmic Rays, Metallicity, and Stellar Dynamics over Cosmic Time
We study the long-term evolution of the Milky Way (MW) over cosmic time by
modeling the star formation, cosmic rays, metallicity, stellar dynamics,
outflows and inflows of the galactic system to obtain various insights into the
galactic evolution. The mass accretion is modeled by the results of
cosmological -body simulations for the cold dark matter. We find that the
star formation rate is about half the mass accretion rate of the disk, given
the consistency between observed Galactic Diffuse X-ray Emissions (GDXEs) and
possible conditions driving the Galactic wind. Our model simultaneously
reproduces the quantities of star formation rate, cosmic rays, metals, and the
rotation curve of the current MW. The most important predictions of the model
are that there is an unidentified accretion flow with a possible number density
of cm and the part of the GDXEs originates from a hot,
diffuse plasma which is formed by consuming about 10 % of supernova explosion
energy. The latter is the science case for future X-ray missions; XRISM,
Athena, and so on. We also discuss further implications of our results for the
planet formation and observations of externalgalaxies in terms of the
multimessenger astronomy.Comment: 17 pages, 10 figures, submitted to PAS
MHD Simulation of The Inner Galaxy with Radiative Cooling and Heating
We investigate the role of magnetic field on the gas dynamics in the Galactic
bulge region by three dimensional simulations with radiative cooling and
heating. While high-temperature corona with is formed in the
halo regions, the temperature near the Galactic plane is following the thermal equilibrium curve determined by the radiative cooling
and heating. Although the thermal energy of the interstellar gas is lost by
radiative cooling, the saturation level of the magnetic field strength does not
significantly depend on the radiative cooling and heating. The magnetic field
strength is amplified to on average, and reaches several
hundred locally. We find the formation of magnetically dominated
regions at mid-latitudes in the case with the radiative cooling and heating,
which is not seen in the case without radiative effect. The vertical thickness
of the mid-latitude regions is at the radial location of
from the Galactic center, which is comparable to the
observed vertical distribution of neutral atomic gas. When we take the average
of different components of energy density integrated over the Galactic bulge
region, the magnetic energy is comparable to the thermal energy. We conclude
that the magnetic field plays a substantial role in controlling the dynamical
and thermal properties of the Galactic bulge region.Comment: Submitted to ApJ; 21 pages, 18 figures 3 tables. Comment are welcom