arXiv subjects

Rikuto Omae

Publications and source records attributed to Rikuto Omae.

4 recordsLinked to original sources

arXiv2026

Probing Magnetic Fields In and Around Galaxies Near and Far

In order to understand the magnetization of galaxies and the role of magnetic fields in feedback processes that govern star formation and galaxy evolution, it is essential to have a comprehensive census of magnetic fields in and around galaxies from the nearby Universe to high redshifts. In this chapter, we outline the science goals, strategies, techniques, and observational requirements with SKA AA4 for (1) a homogeneous polarimetric survey of nearby galaxies - mapping both the diffuse polarized emission as well as producing a dense RM grid within the virial radius; (2) a survey of the interstellar magnetic fields in distant galaxies targeting strong lensing systems with polarized lensed quasars, as well as a general statistical back-illumination survey to probe the redshift evolution of magnetic fields in the CGM. These proposed observations will serve as a major step towards understanding the co-evolution of galaxies and their magnetic fields over cosmic time and provide constraints on galactic dynamo theories.

astro-ph.GA↗

arXiv2022

Effects of Depolarizing Intervening Galaxies on Background Radio Emission I. Global Disk Magnetic Field

External galaxies often intervene in front of background radio sources such as quasars and radio galaxies. Linear polarization of the background emission is depolarized by Faraday rotation of inhomogeneous magnetized plasma of the intervening galaxies. Exploring the depolarizing intervening galaxies (DINGs) can be a powerful tool to investigate the cosmological evolution of the galactic magnetic field. In this paper, we investigate the effects of DINGs on background radio emission using theoretical DING models. We find that complex structures of galaxy result in complicated depolarization features and the Faraday dispersion functions (FDFs), but, for the features of depolarizations and FDFs, the global component of magnetic fields is important. We show the simplest results with ring magnetic field in the galactic disk. We find that the degree of depolarization significantly depends on the inclination angle and the impact parameter of the DING. We found that the larger the standard deviation, the more likely it is that depolarization will occur. The FDF represents the RM structure within the beam. The FDF exhibits multi-components due mainly to the RM structure within the beam and the fraction of the DING that covers the background emission (the filling factor). The peak Faraday depth of the FDF is different from the beam-averaged RM of the DING. The Monte-Carlo simulations indicate that DING's contribution to the standard deviation of observed RMs follows $σ_{\rm RM} \propto 1/{(1+z)^k}$ with $k \sim 2.7$ and exhibits a steeper redshift dependence than the wavelength squared. DINGs will have a significant impact on RM catalogs created by future survey projects such as the SKA and SKA Precursor/Pathfinder.

astro-ph.GA↗

arXiv2021

Continuous Jets and Backflow Models for the Formation of W50/SS433 in Magnetohydrodynamics Simulations

The formation mechanism of the W50/SS433 complex has long been a mystery. We propose a new scenario in which the SS433 jets themselves form the W50/SS433 system. We carry out magnetohydrodynamics simulations of two-side jet propagation using the public code CANS+. As found in previous jet studies, when the propagating jet is lighter than the surrounding medium, the shocked plasma flows back from the jet tip to the core. We find that the morphology of light jets is spheroidal at early times, and afterward, the shell and wings are developed by the broadening spherical cocoon. The morphology strongly depends on the density ratio of the injected jet to the surrounding medium. Meanwhile, the ratio of the lengths of the two-side jets depends only on the density profile of the surrounding medium. We also find that most of the jet kinetic energy is dissipated at the oblique shock formed by the interaction between the backflow and beam flow, rather than at the jet terminal shock. The position of the oblique shock is spatially consistent with the X-ray and TeV gamma-ray hotspots of W50.

astro-ph.HE↗

arXiv2021

Energy estimation of high energy particles associated with the SS433/W50 system through radio observation at 1.4 GHz

The radio nebula W50 is a unique object interacting with the jets of the microquasar SS433. The SS433/W50 system is a good target for investigating the energy of cosmic-ray particles accelerated by galactic jets. We report observations of radio nebula W50 conducted with the NSF's Karl G. Jansky Very Large Array (VLA) in the L band (1.0 -- 2.0 GHz). We investigate the secular change of W50 on the basis of the observations in 1984, 1996, and 2017, and find that most of its structures were stable for 33 years. We revise the upper limit velocity of the eastern terminal filament by half to 0.023$c$ assuming a distance of 5.5 kpc. We also analyze the observational data of the Arecibo Observatory 305-m telescope and identify the HI cavity around W50 in the velocity range 33.77 km s$^{-1}$ -- 55.85 km s$^{-1}$. From this result, we estimate the maximum energy of the cosmic-ray protons accelerated by the jet terminal region to be above 10$^{15.5}$ eV. We also use the luminosity of the gamma-rays in the range 0.5 -- 10 GeV to estimate the total energy of accelerated protons below 5.2 $\times$ 10$^{48}$ erg.

astro-ph.HE↗