投稿者: YamashitaKazuyoshi

Unveiling the Dynamics of Dense Cores in Cluster-Forming Clumps: A 3D MHD Simulation Study of Angular Momentum and Magnetic Field Properties

Speaker: Shinichi Kinoshita

Abstract:

Almost all stars within the Milky Way form as members of clusters. Dense cores, the direct progenitor of stars, are formed in the cluster-forming clumps and eventually form star clusters. Therefore, comprehending the effect of the clump environment on core properties is important for understanding star formation and galaxy evolution.

We conducted isothermal MHD simulations with self-gravity to investigate the properties of dense cores in cluster-forming clumps. Two different setups were explored: a single rotating clump and colliding clumps. We focused on determining the extent to which the rotation and magnetic field of the parental clump are inherited by the formed dense cores. Our statistical analysis revealed that the alignment between the angular momentum of dense cores, Lcore, and the rotational axis of the clump is influenced by the strength of turbulence and the simulation setup. In single rotating clumps, we found that Lcore tends not to align with the clump’s rotational axis unless the initial turbulence is weak. In colliding clumps, however, this alignment does not occur, regardless of the initial turbulence strength. Our analysis of colliding clumps also revealed that the magnetic field globally bends along the shock-compressed layer, and the mean magnetic field of dense cores, Bcore aligns with it. Both in single rotating clumps and colliding clumps, we found that the angle between Bcore and Lcore is generally random, regardless of the clump properties.

Simulating dust monomer collisions: expansion of the JKR theory

Speaker: Yuki Yoshida

Abstract:

Dust is aggregate of monomers. Monomer is minimum building block of dust and have sub-μm size. Dust grows by collisional sticking, but fragmentation can occur for large dust, and the dust growth is stopped. Therefore investigating dust maximum size and critical velocity of sticking is important to understand the dust growth. Numerical simulations of aggregate collisions have investigated the critical velocity of dust compression and disruption, and the dust size evolution (e.g., Wada et al. 2013; Suyama et al. 2012). They used the JKR theory to calculate the monomer interactions. However, dust collision experiments showed that the bouncing velocity is larger than the theoretical value (e.g., Poppe et al. 2000, Wada et al. 2008). It is suggested that this is because the JKR theory does not consider microscopic physics (Tanaka et al. 2015). Therefore, we construct a new contact model by Molecular Dynamics (MD) simulation.
First, we performed MD simulations of monomers’ head-on collisions and investigated the coefficient of restitution, e, changing the monomer size, impact velocity, and temperature. We found that e decreases with decreasing monomer radius, increasing impact velocity larger than 50 m/s and increasing temperature. Next, we extended the contact model by adding dissipative forces to the JKR theory to reproduce the MD results. We found that a dissipative force model proportional to (relative velocity)³ and (contact radius)³/2 can reproduce the MD results well. However, another energy dissipation is required to reproduce the MD simulations for high-velocity collisions. We discuss the MD results and the new model in my presentation.

Two affecting mechanisms on atmospheric carbon of super-Earth: Magma versus Atmospheric escape

Speaker: Chanoul Seo

Abstract :

Super-Earths are the common exoplanets with a few earth radii. The mass and radius of super-Earth correspond to the two compositions, a thicker atmosphere with a silicate core and an H2O-rich composition. Atmospheric characterization is expected to give some hints about their interior.
To find some clues for the super-Earth atmosphere and its connection to the internal structure, previous studies (e.g., Kite et al. 2020, Hu et al. 2021, Yu et al. 2021, and Schlichting+ 2022) discussed the effects of chemical reactions and the planet surfaces on the atmospheric compositions of super-Earths but with assumptions such as artificial atmospheric metallicity, exclusion of magma, or the use of only H and O-bearing volatiles.
In this research, we highlight the magma’s effect on the other radiatively active species, the C-bearing species with the expectation they can be a possible probe of the exposed magma. This effect is compared to the atmospheric escape that also affects the atmospheric composition through selective hydrogen escape. We assume the atmospheric composition before the reaction as the nebula gas-like composition.
We first study the atmospheric compositions of the magma-containing super-Earths, assuming the nebula gas accretion onto the silicate core. We focus on H, O, and C-bearing species. We find that magma can increase the atmospheric C/H ratio by isolating the C-bearing species in the atmosphere because of the much higher solubility of H2O to the magma than the C-bearing species. We quantify this effect by describing the atmospheric C/H ratio as a function of the planetary mass, radius, and equilibrium temperature.
To discuss the energy-limited atmospheric escape, we calculate the resultant atmospheric composition of super-Earth by the atmospheric escape effect. Through the quantitative calculation, we show the effect of the atmospheric escape on the atmospheric C/H ratio with specific planetary age prior as a function of the planetary mass, radius, and orbital radius.
Based on these results, we compare the effect of magma and the effect of atmospheric escape depending on planetary parameters. We also discuss the behavior of another important element　(N, nitrogen) and the influence of various mechanisms, including the convection in magma, that affect the atmospheric C/H ratio.

Weak lensing cosmology with Subaru Hyper Suprime-Cam Year 3 data

Speaker: Sunao Sugiyama and Xiangchong Li

Abstract:

ΛCDM is the standard model of the Universe, which remarkably well explains a wide variety of observational results: accelerating universe via SNe, cosmic microwave background (CMB), and cosmological large-scale structure. Recently, several studies with data from stage-of-the-art galaxy surveys reported the so-called “S₈ tension”, which states the discrepancy in the estimated cosmological-structure growth parameters, S₈, from CMB observation vs. galaxy surveys, but they are still within the statistical uncertainty.
To test the ΛCDM model from the precise measurement of S₈ parameter, we carried out the cosmological weak-lensing analyses using the wide-field imaging survey data by the Subaru Hyper Suprime-Cam (HSC). We constructed the galaxy-shape catalog from imaging data, the calibrated photo-z estimate for our galaxy samples, and the advanced residual PSF modeling. Using these intermediate data, we have performed four independent cosmological analyses in a blind fashion to avoid confirmation bias. We employed very conservative analysis choices against the potential systematics and validated the choices. After unblinding, we got consistent results among these four analyses, each of which gives a 5% constraint on S₈ parameter and indicates 2~2.5 σ level S₈ tension with Planck CMB result.

MHD in a cylindrical shearing box

Speaker: Takeru Suzuki

Abstract:

By performing magnetohydrodynamical (MHD) simulations with weak vertical magnetic fields in unstratified cylindrical and Cartesian shearing boxes, we investigate basic properties of MHD turbulence excited by magnetorotational instability. While both cylindrical and Cartesian cases give a similar level of the time-averaged saturated magnetic field strengths, the cylindrical setup exhibits extremely large time-variability. Detailed analysis of the terms describing magnetic-energy evolution with “triangle diagrams” surprisingly reveals that in the cylindrical simulations, including a case with small curvature, the compression of toroidal magnetic field is unexpectedly as important as the winding due to differential rotation in the amplification of the magnetic field, which is not seen in the Cartesian simulation. This suggests that the physical properties of magnetic evolution in the Cartesian shearing box simulation is fundamentally different even from those in the nearly Cartesian simulation in the cylindrical setup. In addition, the compressible amplification plays a substantial role in triggering intermittent bursty enhancements in magnetic energy observed in the cylindrical simulations. We discuss that {\it the radial gradient of epicycle frequency}, which cannot be handled in the normal Cartesian shearing box model, significantly contributes to the bursty magnetic activity due to compressible amplification. We also introduce a modified prescription for the cylindrical shearing boundary condition.

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.

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.

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.

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.