Mamoru Shimizu

Mass-Temperature Relation of Galaxy Clusters: Implications from the Observed Luminosity-Temperature Relation and X-Ray Temperature Function

We derive constraints on the mass-temperature relation of galaxy clusters from their observed luminosity-temperature relation and X-ray temperature function. Adopting the isothermal gas in hydrostatic equilibrium embedded in the universal density profile of dark matter halos, we compute the X-ray luminosity for clusters as a function of their hosting halo mass. We find that in order to reproduce the two observational statistics, the mass-temperature relation is fairly well constrained as Tgas = (1.5 ~ 2.0) keV(Mvir/1014 h M☉)0.5~0.55, and a simple self-similar evolution model (Tgas ∝ M) is strongly disfavored. In the cosmological model that we assume (a ΛCDM universe with Ω0 = 0.3, λ0 = 0.7, and h70 = 1), the derived mass-temperature relation suggests that the mass fluctuation amplitude σ8 is 0.7-0.8.

A new boranophosphorylation reaction for the synthesis of deoxyribonucleoside boranophosphates

Abstract Deoxyribonucloside 3′-boranophosphate derivatives including adenine, cytosine, guanine, and thymine bases were synthesized in good yields by the use of a new boranophosphorylating reagent. The reaction was successfully applied to the formation of internucleotidic boranophosphate linkages.

Radial profile and lognormal fluctuations of the intracluster medium as the origin of systematic bias in spectroscopic temperature

The origin of the recently reported systematic bias in the spectroscopic temperature of galaxy clusters is investigated using a cosmological hydrodynamic simulation. We find that the local inhomogeneities of the gas temperature and density, after being corrected for their global radial profiles, have a nearly universal distribution that resembles a lognormal function. Based on this lognormal approximation for the fluctuations in the intracluster medium, we develop an analytical model that explains the bias in the spectroscopic temperature. We conclude that the multiphase nature of the intracluster medium, due not only to the radial profiles but also to the local inhomogeneities, plays an essential role in producing the systematic bias.

Reliability of Merger Tree Realizations of Dark Halos in the Monte Carlo Modeling of Galaxy Formation

We examine the reliability of the merger trees generated for the Monte-Carlo modeling of galaxy formation. In particular we focus on the cold gas fraction predicted from the merger trees with different assumptions on the progenitor distribution function, the timestep, and the mass resolution. We show that the cold gas fraction is sensitive to the accuracy of the merger trees at small-mass scales of progenitors at high redshifts. One can reproduce the Press-Schechter prediction to a reasonable degree by adopting a fairly large number of redshift bins, N_{step} ~ 1000 in generating merger trees, which is a factor of ten larger than the canonical value used in previous literature.

Solid-Phase Synthesis of Oligodeoxyribonucleotides without Base Protection Utilizing O-Selective Reaction of Oxazaphospholidine Derivatives

A study on the development of a novel method to synthesize oligodeoxyribonucleotides without base protection is described. We found that nucleoside 3′-O-oxazaphospholidine derivatives exclusively react with the hydroxy group of nucleosides in the presence of unprotected nucleobase amino groups. Since the O-chemoselectivity of the oxazaphospholidine derivatives is likely due to their ring structure, which allows the regeneration of the oxazaphospholidine derivatives from the corresponding base phosphitylation adducts via an intramolecular recyclization, the method is expected to be compatible with any kinds of acidic activators.

Systematic Bias in an Estimate of the Cluster Mass and the Fluctuation Amplitude from Cluster Abundance Statistics

We revisit an estimate of the mass fluctuation amplitude, σ8, from the observational X-ray cluster abundance. In particular, we examine the effect of the systematic difference between the cluster virial mass estimated from the X-ray spectroscopy, Mvir,spec, and the true virial mass of the corresponding halo, Mvir. Mazzotta et al. (2004, MNRAS, 354, 10) recently pointed out the possibility that αM = Mvir,spec/Mvir is systematically lower than unity. We performed a statistical analysis by combining the latest X-ray cluster sample and the improved theoretical models, and found that σ8 ∼0.76 ±0.01 + 0.50(1 − αM )f or 0.5 ≤ αM ≤1, where the quoted errors are only statistical. Thus, if αM ∼ 0.7, the value of σ8 from cluster abundance alone is now in better agreement with other cosmological data, including the cosmic microwave background, the galaxy power spectrum and the weak lensing data. The current study also illustrates the importance of possible systematic effects in mapping real clusters to underlying dark halos, which changes the interpretation of cluster abundance statistics.

Monte Carlo Modeling of Non-Gravitational Heating Processes in Galaxy Clusters

We consider non-gravitational heating effects on galaxy clusters on the basis of the Monte-Carlo modeling of merging trees of dark matter halos combined with the thermal evolution of gas inside each halo. Under the assumption of hydrostatic equilibrium and the isothermal gas profiles, our model takes account of the metallicity evolution, metallicity-dependent cooling of gas, supernova energy feedback, and heating due to jets of radio galaxies in a consistent manner. The observed properties of galaxy clusters can be explained in models with higher non-gravitational heating efficiency than that in the conventional model. Possibilities include jet heating by the Fanaroff-Riley Type II radio galaxies, and the enhanced star formation efficiency and/or supernova energy feedback, especially at high redshifts.

Synthesis of Dinucleoside Boranophosphates by a Boranophosphotriester Approach

Abstract Dinucleoside boranophosphates including four kinds of nucleobases were synthesized by a boranophosphotriester method in good yields. In the present boranophosphotriester method, side-reactions at the nucleobases, which caused by a borane reagent, were completely avoided.

Enhancer and silencer binding proteins involved in the rat cdc2 promoter activation at the G1/S boundary

Expression of the rat cdc2 gene during G1‐S phase progression is negatively and positively regulated by the silencer and enhancer elements located upstream of the basal promoter. The silencer and enhancer sequences resemble each other, but the silencer contains extra internal AG residues.