投稿者: YamashitaKazuyoshi

2023-5-24

Elucidation of galactic magnetic field structure by pseudo-observation based on SPH simulation

Speaker: Yuta Tashima

Abstract:

It is known that the average magnetic field strength of spiral galaxies is about a few micro G, but the structure of the global field has remained unclear parts. Since observables are integral values ​​along the line of sight, it is difficult to obtain a three-dimensional structure. Therefore, we aim to clarify the relationship between the radiation field and the spatial distribution of physical quantities through pseudo-observations using global simulation results. Our previous research adopted the galactic gaseous disk model calculated by MHD simulation, whose calculation assumed a static galactic stellar potential and ignored a cooling effect. Therefore, we thought more realistic results could be obtained using SPH simulation data that considers potential changes due to stellar motion. We calculated the magnetic field using the induction equation from the SPH simulation results and performed a pseudo-observation. As a result, we found that the magnetic field is strongly amplified around the wind blowing from the end of the bar. In the case of an edge-on view, pseudo-observation results can reproduce the X-shape structure often observed in edge-on starburst galaxies. However, the SPH case did not reproduce the magnetic spiral arm structure. This is because SPH solves the induction equation independently, and the result shows the importance of feedback to the motion of the magnetic field.

2023-5-24

Observation of magnetic fields in lensing galaxies using radio polarization data

Speaker: Rikuto Omae

Abstract:

External galaxies often intervene on background radio sources such as quasars and radio galaxies. Linear polarization of the background emission is depolarized by the Faraday rotation of inhomogeneous magnetized plasma of the intervening galaxies. Exploring the depolarizing intervening galaxies can be a powerful tool for investigating the cosmological evolution of the galactic magnetic field. Recently, Mao et al. (2017) detected coherent μG magnetic fields in the lensing disk galaxy by exploiting the scenario where the polarized radio emission from a background source is gravitationally lensed by an intervening galaxy using broadband radio polarization data. The method is based on the difference in Faraday depths, where the background source emission passes through different positions of the intervening galaxies due to the gravitational lensing effect. Using a galactic magnetic field model, we investigate how background polarized sources are observed due to the gravitational lensing effects of intervening galaxies. We will also discuss how this can be observed and applied in real data using the SKA predecessor.

2023-5-17

Core-collapse Supernovae as Laboratories for Axion-like Particles

Speaker: Kanji Mori (NAOJ)

Abstract:

Axion-like particles (ALPs) are a class of hypothetical pseudoscalar particles which feebly interact with ordinary matter. The hot plasma in core-collapse supernovae is a possible laboratory to explore physics beyond the standard model including ALPs. Once produced in a supernova, a part of the ALPs can be absorbed by the supernova matter and affect energy transfer. We recently developed two-dimensional supernova models including the effects of the production and the absorption of ALPs that couple with photons. It is found that the additional heating induced by ALPs can enhance the explosion energy; for moderate ALP-photon coupling, we find explosion energies ~0.6*10^51 erg compared to our reference model without ALPs of ~0.4*10^51 erg. Our findings also indicate that when the coupling constant is sufficiently high, the neutrino luminosities and mean energies are decreased because of the additional cooling of the proto-neutron star. The gravitational wave strain is also reduced because the mass accretion on the proto-neutron star is suppressed.

2023-5-10

Planetary population synthesis model for validation of planet formation theory

speaker: Tadahiro Kimura (NAOJ)

Abstract:

Exoplanet exploration has discovered more than 5000 exoplanets and revealed statistical characteristics of their distribution. These observed distributions are key to validating current theories and advancing our understanding of planet formation processes. For this purpose, we need a model that combines all known formation processes and predicts the current distribution of exoplanets. We have developed a new such model called the planetary population synthesis model and statistically compared its predictions with observed exoplanet distributions. The model deals in detail with the formation and evolution of primordial atmospheres, and by using analytical or empirical models for each elementary process, it can predict observables such as planetary mass, radius and orbital period at a quite low computational cost. This allows comparisons to be made with observations for many model parameter sets. In this study we focus on the distribution of radii and orbital periods of so-called ‘super-Earths’ and ‘sub-Neptunes’ with radii of about 1-4 Earth radii, and investigate whether the observed distribution can be explained within the framework of our model. The results show that the distribution can be reproduced by changing the distribution of initial planetesimals, the disk gas viscosity and the composition of the primordial atmosphere in particular. We predict that both super-Earths and sub-Neptunes have rocky solid cores, and that sub-Neptunes retain their primordial atmospheres enriched with water vapour to this day. These predictions are expected to be verified by future observations of exoplanet atmospheres.