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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 N -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 ∼10−2 cm−3 and that 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 external galaxies in terms of multi-messenger astronomy. [ABSTRACT FROM AUTHOR]

A novel collisionless shock jump condition is suggested by modeling the entropy production at the shock transition region. We also calculate downstream developments of the atomic ionization balance and the ion temperature relaxation in supernova remnants (SNRs). The injection process and subsequent acceleration of cosmic rays (CRs) in the SNR shocks are closely related to the formation process of the collisionless shocks. The formation of the shock is caused by wave–particle interactions. Since the wave–particle interactions result in energy exchanges between electromagnetic fields and charged particles, the randomization of particles associated with the shock transition may occur at a rate given by the scalar product of the electric field and current. We find that order-of-magnitude estimates of the randomization with reasonable strength of the electromagnetic fields in the SNR constrain the amount of CR nuclei and the ion temperatures. The constrained amount of CR nuclei can be sufficient to explain the Galactic CRs. The ion temperature becomes significantly lower than that in the case without CRs. To distinguish the case without CRs, we perform synthetic observations of atomic line emissions from the downstream region of the SNR RCW 86. Future observations by XRISM and Athena can distinguish whether the SNR shock accelerates the CRs or not from the ion temperatures. [ABSTRACT FROM AUTHOR]

A novel diagnostic of cosmic ray modified shocks by polarimetry of H α emissions is suggested. In a cosmic ray modified shock, the pressure of cosmic rays is sufficiently high compared to the upstream ram pressure to force the background plasma to decelerate (measured in the shock rest frame). Simultaneously, a fraction of the hydrogen atoms co-existing in the upstream plasma collide with the decelerated protons and undergo charge-exchange reactions. As a result, hydrogen atoms with the same bulk velocity of the decelerated protons are generated. We show that when the shock is observed from edge-on, the H α radiated by these upstream hydrogen atoms is linearly polarized with a sizable degree of a few per cent as a result of resonant scattering of Ly β. The polarization direction depends strongly on the velocity modification; the direction is parallel to the shock surface for the case of no modification, while the direction is parallel to the shock velocity for the case of a modified shock. [ABSTRACT FROM AUTHOR]

Radiative transfer in hydrogen lines in supernova remnant (SNR) shock waves is studied taking into account the population of the hydrogen atom 2s-state. Measurements of Balmer line emission, especially of H α, are often relied on to derive physical conditions in the SNR shock. On the other hand, Lyman series photons, especially Ly β, are mostly absorbed by upstream hydrogen atoms. As a result, atoms are excited to the 3p state, and then emit H α by the spontaneous transition from 3p to 2s. Thus, the nature of H α depends on how many Ly β photons are converted to H α photons. Moreover, the Balmer lines can be scattered by the 2s-state hydrogen atoms, which are excited not only by collisional excitation but also by the Lyman–Balmer conversion. It is shown for example that the H α photons are scattered if the shock propagates into an H  i cloud with a density of ∼30 cm−3 and a size of ∼1 pc. We find that the line profile of H α becomes asymmetric resulting from the difference between line centre frequencies among the transitions from 3s to 2p, from 3p to 2s, and from 3d to 2p. We also find that the broad-to-narrow ratio of H α, which is often used to estimate the ion-electron temperature equilibrium, varies at most ≃ 10 per cent depending on the ionization degree of the upstream medium because of incomplete conversion of Lyman lines to Balmer lines. [ABSTRACT FROM AUTHOR]

The spectral slope of the magnetic energy in supernova remnants (SNRs) can be obtained by analysis of spatial two-point correlation functions of synchrotron intensities. This method has been originally developed for the analysis of magnetic field structure in diffuse interstellar medium and applied when the geometry of the emission region is simple and known. In this paper, applying this correlation analysis to Tycho 's SNR, for which the synchrotron emission region is known to be a spherical shell, we find that the magnetic energy spectrum shows the Kolmogorov-like scaling. Our results can be explained by turbulence developed downstream of the shock front via Richtmyer–Meshkov instability or an amplification of upstream magnetic field induced by cosmic rays. They could be discriminated by future observations with a sub-arcsecond resolution such as Square Kilometer Array. [ABSTRACT FROM AUTHOR]