arXiv subjects

Fumio Takahara

Publications and source records attributed to Fumio Takahara.

65 records · Page 4Linked to original sources

arXiv2001

Effects of Formation Epoch Distribution on X-Ray Luminosity and Temperature Functions of Galaxy Clusters

We investigate statistical properties of galaxy clusters in the context of hierarchical clustering scenario, taking account of their formation epoch distribution, motivated by the recent finding by Fujita and Takahara that X-ray clusters form a fundamental plane, where the mass and formation epoch are regarded as two independent parameters. Using the formalism which discriminates between major merger and accretion, the epoch of a cluster formation is identified with that of the last major merger. Since tiny mass accretion after the formation does not much affect the core structure of clusters, the properties of X-ray emission from clusters are determined by the total mass and density at their formation time. Under these assumptions, we calculate X-ray luminosity and temperature functions of galaxy clusters. We find that the behavior of luminosity function is different from the model which does not take account of formation epoch distribution, while the behavior of temperature function is not much changed. In our model, luminosity function is shifted to a higher luminosity and shows no significant evolution up to $z \sim 1$, independent of cosmological models. The clusters are populated on the temperature-luminosity plane with a finite dispersion. Since the simple scaling model in which the gas temperature is equal to the virial temperature fails to reproduce the observed luminosity-temperature relation, we also consider a model which takes the effects of preheating into account. The preheating model reproduces the observations much better.

astro-ph↗

arXiv2000

The Variation of Gas Mass Distribution in Galaxy Clusters: Effects of Preheating and Shocks

We investigate the origin of the variation of the gas mass fraction in the core of galaxy clusters, which was indicated by our work on the X-ray fundamental plane. The adopted model supposes that the gas distribution characterized by the slope parameter is related to the preheated temperature. Comparison with observations of relatively hot (~> 3 keV) and low redshift clusters suggests that the preheated temperature is about 0.5-2 keV, which is higher than expected from the conventional galactic wind model and possibly suggests the need for additional heating such as quasars or gravitational heating on the largest scales at high redshift. The dispersion of the preheated temperature may be attributed to the gravitational heating in subclusters. We calculate the central gas fraction of a cluster from the gas distribution, assuming that the global gas mass fraction is constant within a virial radius at the time of the cluster collapse. We find that the central gas density thus calculated is in good agreement with the observed one, which suggests that the variation of gas mass fraction in cluster cores appears to be explained by breaking the self-similarity in clusters due to preheated gas. We also find that this model does not change major conclusions on the fundamental plane and its cosmological implications obtained in previous papers, which strongly suggests that not only for the dark halo but also for the intracluster gas the core structure preserves information about the cluster formation.

astro-ph↗

arXiv1999

Global Relationships among Physical Properties of Galaxy Cluster Cores

Using X-ray data, we investigate interrelations between gas density rho_0, virial density rho_vir, core radius R, temperature T, entropy S_gas, and metal abundance Z in the core region of clusters of galaxies. First, we confirm that fundamental relations among rho_0, R, and T found by Fujita and Takahara are reproduced by another data catalogue. Second, we find that, when clusters have two components in their surface brightness distribution, the inner components also satisfy the same fundamental relations on the assumption that the average temperature of the inner component is the same as that of the outer component. These results strengthen our interpretation that clusters form a two parameter family in terms of mass and rho_vir; larger rho_vir corresponds to earlier formation epoch. We argue that the inner components represent distinct dark matter components which collapsed ahead of the outer components. Third, we also find a tight relation between S_gas and rho_vir both for the outer and inner components; S_gas is smaller for larger rho_vir but is larger than that produced through gravitational collapse alone for larger rho_vir. Although radiative cooling affects the thermal evolution, the tight relationship discovered suggests the existence of stable heating sources or stable energy transmission mechanisms. Finally, we find that the iron abundance at the centers of clusters is correlated with rho_vir for the inner components. This implies that iron produced by Type Ia supernovae has more accumulated for clusters formed earlier. We briefly discuss the implications of these findings.

astro-ph↗

arXiv1999

The X-ray Fundamental Plane and $L_X-T$ Relation of Clusters of Galaxies

We analyze the relations among central gas density, core radius, and temperature of X-ray clusters by plotting the observational data in the three-dimensional ($\log ρ_0$, $\log R$, and $\log T$) space and find that the data lie on a 'fundamental plane'. Its existence implies that the clusters form a two-parameter family. The data on the plane still has a correlation and form a band on the plane. The observed relation $L_{\rm X} \propto T^3$ turns out to be the cross section of the band perpendicular to the major axis, while the major axis is found to describe the virial density. We discuss implications of this two-parameter family nature of X-ray clusters.

astro-ph↗

arXiv1999

Cosmological Implications of the Fundamental Relations of X-ray Clusters

Based on the two-parameter family nature of X-ray clusters of galaxies obtained in a separate paper, we discuss the formation history of clusters and cosmological parameters of the universe. Utilizing the spherical collapse model of cluster formation, and assuming that the cluster X-ray core radius is proportional to the virial radius at the time of the cluster collapse, the observed relations among the density, radius, and temperature of clusters imply that cluster formation occurs in a wide range of redshift. The observed relations favor the low-density universe. Moreover, we find that the model of $n\sim -1$ is preferable.

astro-ph↗

arXiv1998

Measurability of kinetic temperature from metal absorption-line spectra formed in chaotic media

We present a new method for recovering the kinetic temperature of the intervening diffuse gas to an accuracy of 10%. The method is based on the comparison of unsaturated absorption-line profiles of two species with different atomic weights. The species are assumed to have the same temperature and bulk motion within the absorbing region. The computational technique involves the Fourier transform of the absorption profiles and the consequent Entropy-Regularized chi^2-Minimization [ERM] to estimate the model parameters. The procedure is tested using synthetic spectra of CII, SiII and FeII ions. The comparison with the standard Voigt fitting analysis is performed and it is shown that the Voigt deconvolution of the complex absorption-line profiles may result in estimated temperatures which are not physical. We also successfully analyze Keck telescope spectra of CII1334 and SiII1260 lines observed at the redshift z = 3.572 toward the quasar Q1937--1009 by Tytler {\it et al.}.

astro-ph↗

arXiv1998

The D/H ratio at z = 3.57 toward Q 1937-1009

Deuterium abundance re-measurements by Burles and Tytler (1998; hereafter BT) yielded D/H = (3.3 +/- 0.3) 10^{-5} and the robust upper limit D/H < 3.9 10^{-5} from the z_a = 3.572 system toward Q1937-1009. In this new analysis BT adopted multicomponent microturbulent models together with the possibility to vary freely the local continuum level around each HI line to improve the fit. The procedure failed, however, to fit adequately D Ly-beta without recourse to an additional H Ly-alpha contamination at the position of D Ly-beta. We show that this obstacle may be successfully overcome within the framework of the mesoturbulent model accounting (in contrast to the microturbulent approximation) for a correlated structure of the large scale velocity field. Using the same observational data and the original continuum as determined by Tytler et al. (1996), we obtained good fits. The one-component mesoturbulent models provide D/H in the range (3.2 - 4.8) 10^{-5} and the total hydrogen column density N(HI) = (5.6 - 7.0) 10^{17} cm^{-2}. This result is consistent with that found by us from the z_a = 2.504 and z_a = 0.701 systems toward Q1009+2956 and Q1718+4807, respectively. The range for D/H common to all three analyses is D/H = (4.1 - 4.6) 10^{-5}. This value is consistent with standard big bang nucleosynthesis [SBBN] if the baryon-to-photon ratio, η, is in the range 4.2 10^{-10} <= η<= 4.6 10^{-10}, implying 0.0155 <= Ω_b h^2_{100} <= 0.0167.

astro-ph↗

arXiv1998

The D/H ratio at z=0.7 toward Q 1718+4807

The apparent discrepancy between low and high D abundances derived from QSO spectra may be caused by spatial correlations in the stochastic velocity field. If one accounts for such correlations, one finds good agreement between different observations and the theoretical predictions for standard big bang nucleosynthesis (SBBN). In particular, we show that the H+D Ly-alpha profile observed at z = 0.7 toward Q1718+4807 is compatible with 4.1*10^{-5} <= D/H <= 4.7*10^{-5}. This result is consistent with our previous D/H determination for the z = 2.504 system toward Q1009+2956 and, thus, supports SBBN.

astro-ph↗

arXiv1997

Primordial Deuterium Abundance Measurements

Deuterium abundances measured recently from QSO absorption-line systems lie in the range from 3 10^{-5} to 3 10^{-4}, which shed some questions on standard big bang theory. We show that this discordance may simply be an artifact caused by inadequate analysis ignoring spatial correlations in the velocity field in turbulent media. The generalized procedure (accounting for such correlations) is suggested to reconcile the D/H measurements. An example is presented based on two high-resolution observations of Q1009+2956 (low D/H) [1,2] and Q1718+4807 (high D/H) [8,9]. We show that both observations are compatible with D/H = 4.1 - 4.6 10^{-5}, and thus support SBBN. The estimated mean value = 4.4 10^{-5} corresponds to the baryon-to-photon ratio during SBBN eta = 4.4 10^{-10} which yields the present-day baryon density Omega_b h^2 = 0.015.

astro-ph↗

arXiv1997

The primordial deuterium abundance : problems and prospects

The current status of extragalactic deuterium abundance is discussed using two examples of `low' and `high' D/H measurements. We show that the discordance of these two types of D abundances may be a consequence of the spatial correlations in the stochastic velocity field. Within the framework of the generalized procedure (accounting for such effects) one finds good agreement between different observations and the theoretical predictions for standard big bang nucleosynthesis (SBBN). In particular, we show that the deuterium absorption seen at z = 2.504 toward Q1009+2956 and the H+D Ly-alpha profile observed at z = 0.701 toward Q1718+4807 are compatible with D/H $\sim 4.1 - 4.6\times10^{-5}$. This result supports SBBN and, thus, no inhomogeneity is needed. The problem of precise D/H measurements is discussed.

astro-ph↗

arXiv1994

Implications on the Ionizing Background Radiation from HST Heii Gunn-Peterson Test

Recently, Jakobsen et al. reported that the HeII Gunn-Peterson optical depth is greater than 1.7 at $ z=3.3$. When we consider this observation combined with the HI Gunn-Peterson optical depths and the intensity of the UV background at high redshifts, we can put constraints on the spectrum of the UV background and the mass fraction of intergalactic medium. We find that the spectrum must be steep ($α\gsim 3; J_ν \propto ν^{-α} $) to be consistent with observations, and that the mass fraction of the intergalactic medium must be greater than 0.3 (0.1) in the case $ α=3 (4)$ for baryon density consistent with the primordial nucleosynthesis. We also find that HeII fraction is as low as $10^{-3} \sim 10^{-1} $ even for this steep spectrum.

astro-ph↗