Clustering of dark matter halos on the light-cone: scale-, time- and mass-dependence of the halo biasing in the Hubble volume simulations

We develop a phenomenological model to predict the clustering of dark matter halos on the light-cone by combining several existing theoretical models. Assuming that the velocity field of halos on large scales is approximated by linear theory, we propose an empirical prescription of a scale-, mass-, and time-dependence of halo biasing. We test our model against the Hubble Volume $N$-body simulation and examine its validity and limitations. We find a good agreement in two-point correlation functions of dark matter halos between the phenomenological model predictions and measurements from the simulation for $R>5h^{-1}$Mpc both in the real and redshift spaces. Although calibrated on the mass scale of groups and clusters and for redshifts up to $z\sim2$, the model is quite general and can be applied to a wider range of astrophysical objects, such as galaxies and quasars, if the relation between dark halos and visible objects is specified.Comment: 5 pages, 2 figures, ApJL accepted. New references adde

Quantitative studies for photoabsorption and fluorescence of HCl

Photoabsorption and fluorescence cross sections of HCl are investigated in the wavelength region between 105 to 220 nm. The oscillator strengths of discrete structures at wavelengths shorter than 130 nm are measured

Power Spectrum Analysis of the 2dF QSO Sample Revisited

We revisit the power spectrum analysis of the complete sample of the two degree field (2dF) QSO redshift (2QZ) survey, as a complementary test of the work by Outram et al. (2003). A power spectrum consistent with that of the 2QZ group is obtained. Differently from their approach, fitting of the power spectrum is investigated incorporating the nonlinear effects, the geometric distortion and the light-cone effect. It is shown that the QSO power spectrum is consistent with the $\Lambda$ cold dark matter (CDM) model with the matter density parameter $\Omega_m=0.2\sim0.5$. Our constraint on the density parameter is rather weaker than that of the 2QZ group. We also show that the constraint slightly depends on the equation of state parameter $w$ of the dark energy. The constraint on $w$ from the QSO power spectrum is demonstrated, though it is not very tight.Comment: 15 pages, 5 figures, accepted for publication in the Astrophysical Journa

Reconstructing Three-dimensional Structure of Underlying Triaxial Dark Halos From Xray and Sunyaev-Zel'dovich Effect Observations of Galaxy Clusters

While the use of galaxy clusters as {\it tools} to probe cosmology is established, their conventional description still relies on the spherical and/or isothermal models that were proposed more than 20 years ago. We present, instead, a deprojection method to extract their intrinsic properties from X-ray and Sunyaev--Zel'dovich effect observations in order to improve our understanding of cluster physics. First we develop a theoretical model for the intra-cluster gas in hydrostatic equilibrium in a triaxial dark matter halo with a constant axis ratio. In this theoretical model, the gas density profiles are expressed in terms of the intrinsic properties of the dark matter halos. Then, we incorporate the projection effect into the gas profiles, and show that the gas surface brightness profiles are expressed in terms of the eccentricities and the orientation angles of the dark halos. For the practical purpose of our theoretical model, we provide several empirical fitting formulae for the gas density and temperature profiles, and also for the surface brightness profiles relevant to X-ray and Sunyaev--Zel'dovich effect observations. Finally, we construct a numerical algorithm to determine the halo eccentricities and orientation angles using our model, and demonstrate that it is possible in principle to reconstruct the 3D structures of the dark halos from the X-ray and/or Sunyaev-Zel'dovich effect cluster data alone without requiring priors such as weak lensing informations and without relying on such restrictive assumptions as the halo axial symmetry about the line-of-sight.Comment: Accepted version, new discussions added, typos and minor mistakes corrected, ApJ in press (2004, Feb. 1 scheduled, Vol. 601, No. 2 issue),26 pages, 7 postscript figure

OH(A-X) fluorescence from photodissociative excitation of HO2 at 157.5 nm

The OH(A-X) fluorescence from photodissociative excitation of HO2 by F2 laser photons (157.5 nm) was observed and compared with the OH fluorescence spectra of H2O2 and the O2+CH3OH mixture. The rotational population distributions of OH(A) were obtained from the fluorescence spectra. The most populated levels are J = 4 for photodissociative excitation of HO2, J = 20 for H2O2, and J = 21 for the O2+CH3OH mixture. The fluorescence from the gas mixture is attributed to the O + H recombination for which the atoms are produced from photodissociation of parent molecules

Can Geometric Test Probe the Cosmic Equation of State ?

Feasibility of the geometric test as a probe of the cosmic equation of state of the dark energy is discussed assuming the future 2dF QSO sample. We examine sensitivity of the QSO two-point correlation functions, which are theoretically computed incorporating the light-cone effect and the redshift distortions, as well as the nonlinear effect, to a bias model whose evolution is phenomenologically parameterized. It is shown that the correlation functions are sensitive on a mean amplitude of the bias and not to the speed of the redshift evolution. We will also demonstrate that an optimistic geometric test could suffer from confusion that a signal from the cosmological model can be confused with that from a stochastic character of the bias.Comment: 11 pages, including 3 figures, accepted for publication in ApJ