Masakazu A. R. Kobayashi

Extragalactic Background Light from Hierarchical Galaxy Formation: Gamma-ray Attenuation up to the Epoch of Cosmic Reionization and the First Stars

We present a new model of the extragalactic background light (EBL) and corresponding γγ opacity for intergalactic gamma-ray absorption from z = 0 up to z = 10, based on a semi-analytical model of hierarchical galaxy formation that reproduces key observed properties of galaxies at various redshifts. Including the potential contribution from Population III stars and following the cosmic reionization history in a simplified way, the model is also broadly consistent with available data concerning reionization, particularly the Thomson scattering optical depth constraints from Wilkinson Microwave Anisotropy Probe (WMAP). In comparison with previous EBL studies up to z ~ 3-5, our predicted γγ opacity is in general agreement for observed gamma-ray energy below 400/(1 + z) GeV, whereas it is a factor of ~2 lower above this energy because of a correspondingly lower cosmic star formation rate, even though the observed ultraviolet (UV) luminosity is well reproduced by virtue of our improved treatment of dust obscuration and direct estimation of star formation rate. The horizon energy at which the gamma-ray opacity is unity does not evolve strongly beyond z ~ 4 and approaches ~20 GeV. The contribution of Population III stars is a minor fraction of the EBL at z = 0, and is also difficult to distinguish through gamma-ray absorption in high-z objects, even at the highest levels allowed by the WMAP constraints. Nevertheless, the attenuation due to Population II stars should be observable in high-z gamma-ray sources by telescopes such as Fermi or the Cherenkov Telescope Array and provide a valuable probe of the evolving EBL in the rest-frame UV. The detailed results of our model are publicly available in numerical form at http://www.slac.stanford.edu/~yinoue/Download.html.

The ν2GC simulations: Quantifying the dark side of the universe in the Planck cosmology

We present the evolution of dark matter halos in six large cosmological N-body simulations, called the

ANTI-HIERARCHICAL EVOLUTION OF THE ACTIVE GALACTIC NUCLEUS SPACE DENSITY IN A HIERARCHICAL UNIVERSE

\nu^2

Evolution of the Fraction of Clumpy Galaxies at 0.2

GC (New Numerical Galaxy Catalog) simulations on the basis of the LCDM cosmology consistent with observational results obtained by the Planck satellite. The largest simulation consists of

< z <

8192^3

1.0 in the COSMOS Field

(550 billion) dark matter particles in a box of

DISCOVERY OF MASSIVE, MOSTLY STAR FORMATION QUENCHED GALAXIES WITH EXTREMELY LARGE Lyα EQUIVALENT WIDTHS AT z ∼ 3*

1.12 \, h^{-1} \rm Gpc

The Subaru COSMOS 20: Subaru optical imaging of the HST COSMOS field with 20 filters

(a mass resolution of

A New Chemical Evolution Model for Dwarf Spheroidal Galaxies Based on Observed Long Star Formation Histories

2.20 \times 10^{8} \, h^{-1} M_{\odot}

The impact of dust in host galaxies on quasar luminosity functions

). Among simulations utilizing boxes larger than