Ryosuke S. Asano

Dust formation history of galaxies: a critical role of metallicity for the dust mass growth by accreting materials in the interstellar medium

This paper investigates the main driver of dust mass growth in the interstellar medium (ISM) by using a chemical evolution model of a galaxy with metals (elements heavier than helium) in the dust phase, in addition to the total amount of metals. We consider asymptotic giant branch (AGB) stars, type II supernovae (SNe II), and dust mass growth in the ISM, as the sources of dust, and SN shocks as the destruction mechanism of dust. Furthermore, to describe the dust evolution precisely, our model takes into account the age and metallicity (the ratio of metal mass to ISM mass) dependence of the sources of dust. We have particularly focused on the dust mass growth, and found that in the ISM this is regulated by the metallicity. To quantify this aspect, we introduce a “critical metallicity”, which is the metallicity at which the contribution of stars (AGB stars and SNe II) equals that of the dust mass growth in the ISM. If the star-formation timescale is shorter, the value of the critical metallicity is higher, but the galactic age at which the metallicity reaches the critical metallicity is shorter. From observations, it was expected that the dust mass growth was the dominant source of dust in the Milky Way and dusty QSOs at high redshifts. By introducing a critical metallicity, it is clearly shown that the dust mass growth is the main source of dust in such galaxies with various star-formation timescales and ages. The dust mass growth in the ISM is regulated by metallicity, and we emphasize that the critical metallicity serves as an indicator to judge whether the grain growth in the ISM is the dominant source of dust in a galaxy, especially because of the strong, and nonlinear, dependence on the metallicity.

What determines the grain size distribution in galaxies

Dust in galaxies forms and evolves by various processes, and these dust processes change the grain size distribution and amount of dust in the interstellar medium (ISM). We construct a dust evolution model taking into account the grain size distribution, and investigate what kind of dust processes determine the grain size distribution at each stage of galaxy evolution. In addition to the dust production by Type II supernovae (SNe II) and asymptotic giant branch (AGB) stars, we consider three processes in the ISM: (i) dust destruction by SN shocks, (ii) metal accretion on to the surface of pre-existing grains in the cold neutral medium (CNM; called grain growth) and (iii) grain–grain collisions (shattering and coagulation) in the warm neutral medium and CNM. We found that the grain size distribution in galaxies is controlled by stellar sources in the early stage of galaxy evolution, and that afterwards the main processes that govern the size distribution changes to those in the ISM, and this change occurs at earlier stage of galaxy evolution for a shorter star formation time-scale (for star formation time-scales = 0.5, 5 and 50 Gyr, the change occurs about galactic aget ∼ 0.6, 2 and 5 Gyr, respectively). If we only take into account the processes which directly affect the total dust mass (dust production by SNe II and AGB stars, dust destruction by SN shocks and grain growth), the grain size distribution is biased to large grains (a ∼ 0.2–0.5 μm, where a is the grain radius). Therefore, shattering is crucial to produce small (a 0.01 μm) grains. Since shattering produces a large abundance of small grains (consequently, the surface-to-volume ratio of grains increases), it enhances the efficiency of grain growth, contributing to the significant increase of the total dust mass. Grain growth creates a large bump in the grain size distribution around a ∼ 0.01 μm. Coagulation occurs effectively after the number of small grains is enhanced by shattering, and the grain size distribution is deformed to have a bump at a ∼ 0.03–0.05 μ ma tt ∼ 10 Gyr. We conclude that the evolutions of the total dust mass and the grain size distribution in galaxies are closely related to each other, and the grain size distribution changes considerably through the galaxy evolution because the dominant dust processes which regulate the grain size distribution change.

Cross-Cultural Validation of Fear of Happiness Scale Across 14 National Groups

A survey of the cultural notions related to happiness and the existing empirical evidence indicate that some individuals endorse the belief that happiness, particularly an immoderate degree of it, should be avoided. These beliefs mainly involve the general notion that happiness may lead to bad things happening. Using multigroup confirmatory factor analysis and multilevel modeling, this study investigates the measurement invariance, cross-level isomorphism, predictive validity, and nomological network of the fear of happiness scale across 14 nations. The results show that this scale has good statistical properties at both individual and cultural levels. The findings also indicate that this scale has the potential to add to the knowledge about how people conceive of, and experience, happiness across cultures.

Evolution of extinction curves in galaxies

We investigate the evolution of extinction curves in galaxies based on our evolution model of grain size distribution. In this model, we considered various processes: dust formation by SNe II and AGB stars, dust destruction by SN shocks in the ISM, metal accretion onto the surface of grains (referred to as grain growth), shattering and coagulation. We find that the extinction curve is flat in the earliest stage of galaxy evolution. As the galaxy is enriched with dust, shattering becomes effective to produce a large abundance of small grains (

Evolution of grain size distribution in high-redshift dusty quasars: integrating large amounts of dust and unusual extinction curves

a \la 0.01\;\mu

Formation history of polycyclic aromatic hydrocarbons in galaxies

m). Then, grain growth becomes effective at small grain radii, forming a bump at

Dense molecular cloud cores as a source of micrometer-sized grains in galaxies

a \sim 10^{-3}

How do the extinction curves in galaxies evolve

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Gas-to-dust mass ratios in local galaxies over a 2 dex metallicity range

10^{-2}\;\mu

Fragility of happiness beliefs across 15 national groups

m on the grain size distribution. Consequently, the extinction curve at ultraviolet (UV) wavelengths becomes steep, and a bump at