Formulation of Non-steady-state Dust Formation Process in Astrophysical Environments

The non-steady-state formation of small clusters and the growth of grains accompanied by chemical reactions are formulated under the consideration that the collision of key gas species (key molecule) controls the kinetics of dust formation process. The formula allows us to evaluate the size distribution and condensation efficiency of dust formed in astrophysical environments. We apply the formulation to the formation of C and MgSiO3 grains in the ejecta of supernovae, as an example, to investigate how the non-steady effect influences the formation process, condensation efficiency f_{con}, and average radius a_{ave} of newly formed grains in comparison with the results calculated with the steady-state nucleation rate. We show that the steady-state nucleation rate is a good approximation if the collision timescale of key molecule tau_{coll} is much smaller than the timescale tau_{sat} with which the supersaturation ratio increases; otherwise the effect of the non-steady state becomes remarkable, leading to a lower f_{con} and a larger a_{ave}. Examining the results of calculations, we reveal that the steady-state nucleation rate is applicable if the cooling gas satisfies Lambda = tau_{sat}/tau_{coll} > 30 during the formation of dust, and find that f_{con} and a_{ave} are uniquely determined by Lambda_{on} at the onset time t_{on} of dust formation. The approximation formulae for f_{con} and a_{ave} as a function of Lambda_{on} could be useful in estimating the mass and typical size of newly formed grains from observed or model-predicted physical properties not only in supernova ejecta but also in mass-loss winds from evolved stars.Comment: 44 pages, 10 figures, 1 table, accepted for publication in Ap

Wormhole C-metric

The C-metric in vacuum general relativity describes a pair of accelerated black holes supported by conical singularity. In this paper, we present a new family of exact solutions to the Einstein-phantom scalar system that describes accelerated wormholes in AdS. In the zero acceleration limit with a vanishing potential, the present solution recovers the asymptotically flat wormhole originally constructed by Ellis and Bronnikov. The scalar potential of the phantom field has an infinite number of critical points and is expressed in terms of the superpotential, which is obtained by suitable analytic continuation of one parameter family of the ${\cal N}=2$ gauged supergravity. As one traverses two asymptotic regions connected by throat, the scalar field evolves from AdS, corresponding to the origin of the potential, towards the neighboring AdS local minimum of the potential. We find that the flipping transformation, which interchanges the role of ``radial'' and "angular'' coordinates at the expense of double Wick rotation, is an immediate cause for the existence of two branches of static AdS wormholes discovered previously. Contrary to the ordinary C-metric, the conical singularity along the symmetry axis can be completely resolved, when the (super)potential is periodic or zero. We explore the global causal structure in detail.Comment: 17 pages, 5 figure

A model for the infrared dust emission from forming galaxies

In the early epoch of galaxy evolution, dust is only supplied by supernovae (SNe). With the aid of a new physical model of dust production by SNe developed by Nozawa et al. (2003) (N03), we constructed a model of dust emission from forming galaxies on the basis of the theoretical framework of Takeuchi et al. (2003) (T03). N03 showed that the produced dust species depends strongly on the mixing within SNe. We treated both unmixed and mixed cases and calculated the infrared (IR) spectral energy distribution (SED) of forming galaxies for both cases. Our model SED is less luminous than the SED of T03 model by a factor of 2-3. The difference is due to our improved treatment of UV photon absorption cross section, as well as different grain size and species newly adopted in this work. The SED for the unmixed case is found to have an enhanced near to mid-IR (N-MIR) continuum radiation in its early phase of the evolution (age < 10^{7.25} yr) compared with that for the mixed case. The strong N--MIR continuum is due to the emission from Si grains, which only exist in the species of the unmixed dust production. We also calculated the IR extinction curves for forming galaxies. Then we calculated the SED of a local starbursting dwarf galaxy SBS 0335-052. Our present model SED naturally reproduced the strong N--MIR continuum and the lack of cold FIR emission of SBS 0335-052. We found that only the SED of unmixed case can reproduce the NIR continuum of this galaxy. We then made a prediction for the SED of another typical star-forming dwarf, I Zw 18. We also presented the evolution of the SED of LBGs. Finally, we discussed the possibility of observing forming galaxies at z > 5.Comment: MNRAS, in press. 18 pages, 15 figures. Abstract abridge

Dust Production Factories in the Early Universe: Formation of Carbon Grains in Red-supergiant Winds of Very Massive Population III Stars

We investigate the formation of dust in a stellar wind during the red-supergiant (RSG) phase of a very massive Population III star with the zero-age main sequence mass of 500 M_sun. We show that, in a carbon-rich wind with a constant velocity, carbon grains can form with a lognormal-like size distribution, and that all of the carbon available for dust formation finally condense into dust for wide ranges of the mass-loss rate ((0.1-3)x10^{-3} M_sun yr^{-1}) and wind velocity (1-100 km s^{-1}). We also find that the acceleration of the wind driven by newly formed dust suppresses the grain growth but still allows more than half of gas-phase carbon to be finally locked up in dust grains. These results indicate that at most 1.7 M_sun of carbon grains can form in total during the RSG phase of 500 M_sun Population III stars. Such a high dust yield could place very massive primordial stars as important sources of dust at the very early epoch of the universe if the initial mass function of Population III stars was top-heavy. We also briefly discuss a new formation scenario of carbon-rich ultra-metal-poor stars considering the feedback from very massive Population III stars.Comment: 1 table, 4 figures, accepted for publication in the ApJ Letter

Constraining the amount of circumstellar matter and dust around Type Ia supernovae through near-infrared echoes

The circumstellar (CS) environment is key to understanding progenitors of type Ia supernovae (SNe Ia), as well as the origin of a peculiar extinction property toward SNe Ia for cosmological application. It has been suggested that multiple scatterings of SN photons by CS dust may explain the non-standard reddening law. In this paper, we examine the effect of re-emission of SN photons by CS dust in the infrared (IR) wavelength regime. This effect allows the observed IR light curves to be used as a constraint on the position/size and the amount of CS dust. The method was applied to observed near-infrared (NIR) SN Ia samples; meaningful upper limits on the CS dust mass were derived even under conservative assumptions. We thereby clarify a difficulty associated with the CS dust scattering model as a general explanation for the peculiar reddening law, while it may still apply to a sub-sample of highly reddened SNe Ia. For SNe Ia in general, the environment at the interstellar scale appears to be responsible for the non-standard extinction law. Furthermore, deeper limits can be obtained using the standard nature of SN Ia NIR light curves. In this application, an upper limit of Mdot ~10^{-8}-10^{-7} Msun/yr (for the wind velocity of ~10 km/s) is obtained for a mass loss rate from a progenitor up to ~0.01 pc, and Mdot ~10^{-7}-10^{-6} Msun/yr up to ~0.1 pc.Comment: 13 pages, 12 figures. Accepted for publication in MNRA

Evolution of newly formed dust in Population III supernova remnants and its impact on the elemental composition of Population II.5 stars

We investigate the evolution of dust formed in Population III supernovae (SNe) by considering its transport and processing by sputtering within the SN remnants (SNRs). We find that the fates of dust grains within SNRs heavily depend on their initial radii $a_{\rm ini}$. For Type II SNRs expanding into the ambient medium with density of $n_{\rm H,0} = 1$ cm$^{-3}$, grains of $a_{\rm ini} < 0.05$ $\mu$m are detained in the shocked hot gas and are completely destroyed, while grains of $a_{\rm ini} > 0.2$ $\mu$m are injected into the surrounding medium without being destroyed significantly. Grains with $a_{\rm ini}$ = 0.05-0.2 $\mu$m are finally trapped in the dense shell behind the forward shock. We show that the grains piled up in the dense shell enrich the gas up to 10$^{-6}-10^{-4}$ $Z_\odot$, high enough to form low-mass stars with 0.1-1 $M_\odot$. In addition, [Fe/H] in the dense shell ranges from -6 to -4.5, which is in good agreement with the ultra-metal-poor stars with [Fe/H] < -4. We suggest that newly formed dust in a Population III SN can have great impacts on the stellar mass and elemental composition of Population II.5 stars formed in the shell of the SNR.Comment: 5 pages, 3 figures and 1 table. To appear in the proceedings of IAU Symposium 255 "Low-Metallicity Star Formation: From the First Stars to Dwarf Galaxies", Rapallo, June 2008, eds. L.K. Hunt, S. Madden, & R. Schneider (Cambridge Univ. Press

Intracellular Group A Streptococcus Induces Golgi Fragmentation To Impair Host Defenses through Streptolysin O and NAD-Glycohydrolase

人食いバクテリアの新たな免疫回避機構を発見. 京都大学プレスリリース. 2021-02-15.Group A Streptococcus (GAS; Streptococcus pyogenes) is a major human pathogen that causes streptococcal pharyngitis, skin and soft tissue infections, and life-threatening conditions such as streptococcal toxic-shock syndrome. During infection, GAS not only invades diverse host cells but also injects effector proteins such as NAD-glycohydrolase (Nga) into the host cells through a streptolysin O (SLO)-dependent mechanism without invading the cells; Nga and SLO are two major virulence factors that are associated with increased bacterial virulence. Here, we have shown that the invading GAS induces fragmentation of the Golgi complex and inhibits anterograde transport in the infected host cells through the secreted toxins SLO and Nga. GAS infection-induced Golgi fragmentation required both bacterial invasion and SLO-mediated Nga translocation into the host cytosol. The cellular Golgi network is critical for the sorting of surface molecules and is thus essential for the integrity of the epithelial barrier and for the immune response of macrophages to pathogens. In epithelial cells, inhibition of anterograde trafficking by invading GAS and Nga resulted in the redistribution of E-cadherin to the cytosol and an increase in bacterial translocation across the epithelial barrier. Moreover, in macrophages, interleukin-8 secretion in response to GAS infection was found to be suppressed by intracellular GAS and Nga. Our findings reveal a previously undescribed bacterial invasion-dependent function of Nga as well as a previously unrecognized GAS-host interaction that is associated with GAS pathogenesis