Akio K. Inoue

Gamma-Ray Burst Formation Rate Inferred from the Spectral Peak Energy-Peak Luminosity Relation

We estimate a gamma-ray burst (GRB) formation rate based on the new relation between the spectral peak energy (Ep) and the peak luminosity. The new relation is derived by combining the data of Ep and the peak luminosities by BeppoSAX and BATSE, and it looks considerably tighter and more reliable than the relations suggested by the previous works. Using the new Ep-luminosity relation, we estimate redshifts of the 689 GRBs without known distances in the BATSE catalog and derive a GRB formation rate as a function of the redshift. For the redshift range of 0 ≤ z ≤ 2, the GRB formation rate increases and is well correlated with the star formation rate, while it keeps constant toward z ~ 12. We also discuss the luminosity function and the redshift dependence of the intrinsic luminosity (luminosity evolution).

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.

VLT narrow-band photometry in the Lyman continuum of two galaxies at z ∼ 3 : Limits to the escape of ionizing flux

We have performed narrow-band imaging observations with the Very Large Telescope, aimed at detecting the Lyman continuum (LC) flux escaping from galaxies at z~3. We do not find any significant LC flux from our sample of two galaxies in the Hubble Deep Field South, at z=3.170 and 3.275. The corresponding lower limits on the F_{1400}/F_{900} flux density (per Hz) ratio are 15.6 and 10.2 (3-sigma confidence level). After correction for the intergalactic hydrogen absorption, the resulting limits on the relative escape fraction of the LC are compared with those obtained by different approaches, at similar or lower redshifts. One of our two objects has a relative escape fraction lower than the detection reported by Steidel et al. in a composite spectrum of z~3 galaxies. A larger number of objects is required to reach a significant conclusion. Our comparison shows the potential of narrow-band imaging for obtaining the best limit on the relative escape fraction at z~3. Stacking a significant number of galaxies observed through a narrow-band filter would provide constraint on the galactic contribution to the cosmic reionization.

Evolution of Dust-to-Metal Ratio in Galaxies

This paper investigates the evolution of the dust-to-metal ratio in galaxies based on a simple evolution model for the amount of metal and dust with infall. We take into account grain formation in stellar mass-loss gas, grain growth by the accretion of metallic atoms in a cold dense cloud, and grain destruction by SNe shocks. Especially, we propose that the accretion efficiency is independent of the star-formation history. This predicts various evolutionary tracks in the metallicity (

Spatial Distribution of Dust Grains within H II Regions

Z

Conversion Law of Infrared Luminosity to Star Formation Rate for Galaxies

)--dust-to-gas ratio (

Constraint on intergalactic dust from thermal history of intergalactic medium

\cal D

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

) plane depending on the star-formation history. In this framework, the observed linear

Emission from dust in galaxies: Metallicity dependence

Z

Spectroscopy and stellar populations of star-forming galaxies at z ~ 3 in the Hubble Deep Field – South

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