Hideyuki Kamaya

Dust-to-gas ratio and star formation history of blue compact dwarf galaxies

This paper investigates the origin of the observed large variety in dust-to-gas ratio, D, among blue compact dwarf galaxies (BCDs). By applying our chemical evolution model, we nd that the dust destruction can largely suppress the dust-to-gas ratio when the metallicity of a BCD reaches 12 + log (O=H) 8, i.e., a typical metallicity level of BCDs. We also show that dust-to-gas ratio is largely varied owing to the change of dust destruction eciency that has two eects: (i) a signicant contribution of Type Ia supernovae to total supernova rate; (ii) variation of gas mass contained in a star-forming region. While mass loss from BCDs was previously thought to be the major cause for the variance ofD, we suggest that the other two eects are also important. We nally discuss the intermittent star formation history, which naturally explains the large dispersion of dust-to-gas ratio among BCDs.

Effect of Dust Extinction on Estimating the Star Formation Rate of Galaxies: Lyman Continuum Extinction

We reexamine the effect of Lyman continuum (λ ≤ 912 A) extinction (LCE) by dust in H II regions in detail and discuss how it affects the estimation of the global star formation rate (SFR) of galaxies. To clarify the first issue, we establish two independent methods for estimating a parameter of LCE (f), which is defined as the fraction of Lyman continuum photons contributing to hydrogen ionization in an H II region. One of those methods determines f from the set of Lyman continuum flux, electron density, and metallicity. In the framework of this method, as the metallicity and/or the Lyman photon flux increase, f is found to decrease. The other method determines f from the ratio of infrared flux to Lyman continuum flux. Importantly, we show that f 0.5 via both methods in many H II regions of the Galaxy. Thus, it establishes that dust in such H II regions absorbs significant amount of Lyman continuum photons directly. To examine the second issue, we approximate f to a function of only the dust-to-gas mass ratio (i.e., metallicity), assuming a parameter fit for the Galactic H II regions. We find that a characteristic , which is defined as f averaged over a galaxywide scale, is 0.3 for the nearby spiral galaxies. This relatively small indicates that a typical increment factor due to LCE for estimating the global SFR (1/) is large (~3) for the nearby spiral galaxies. Therefore, we conclude that the effect of LCE is not negligible relative to other uncertainties of estimating the SFR of galaxies.

Small Structures via Thermal Instability of Partially Ionized Plasma. I. Condensation Mode

Thermal instability of partially ionized plasma is investigated by means of a linear perturbation analysis. The previous studies under the one-fluid approach did not precisely consider the effect of the ion-neutral friction, since they did not treat the flow as two fluids which are composed of ions and neutrals. Then, we revisit the effect of the ion-neutral friction of the two fluid on the growth of the thermal instability. According to our study: (1) The instability which is characterized by the mean molecular weight of neutrals is suppressed via the friction only when the magnetic field and the friction are sufficiently strong. The suppression owing to the friction occurs even along the field line. If the magnetic field and the friction are not so strong, the instability is not stabilized. (2) The effect of the friction and the magnetic field is mainly reduction of the growth rate of the instability. (3) The effect of friction does not affect the critical wavelength λF for the instability. This yields that λF is not enlarged even when the magnetic field exists. We insist that the thermal instability of the weakly ionized plasma in the magnetic field can grow up even at the small length scale where the instability under the assumption of the one-fluid plasma cannot grow owing to the stabilization by the magnetic field. (4) The wavelength of the maximum growth rate shifts shortward according to the decrement of the growth rate. Therefore, smaller structures than those without the friction are expected to appear. Our results indicate that the friction with the magnetic field affects the morphology and evolution of the interstellar matter.

Conversion Law of Infrared Luminosity to Star Formation Rate for Galaxies

We construct a new algorithm for estimating the star formation rate (SFR) of galaxies from their infrared (IR) luminosity by developing the theory of the IR emission from a dusty H II region. The derived formula is

Frozen Condition for the Charged Particles in Molecular Clouds

{\rm SFR}/(\MO {\rm yr^{-1}})=\{3.3\times 10^{-10}(1-\eta)/ (0.4-0.2f+0.6 \epsilon)\}(L{\rm ^{obs}_{IR}}/\LO)

Constraint on intergalactic dust from thermal history of intergalactic medium

, where

Amount of intergalactic dust: constraints from distant supernovae and the thermal history of the intergalactic medium

f

Emission from dust in galaxies: Metallicity dependence

is the fraction of ionizing photons absorbed by hydrogen,

Interstellar Mass Outflow to Galactic Halos by the Supernova-Driven Parker Instability

\epsilon

On the possibility of observing H2 emission from primordial molecular cloud kernels

is the efficiency of dust absorption for nonionizing photons from OB stars, and