arXiv subjects

Tetsu Kitayama

Publications and source records attributed to Tetsu Kitayama.

72 records · Page 4Linked to original sources

arXiv2003

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.

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arXiv2003

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 very tightly constrained as T_{gas} = (1.5~2.0)keV (M_{vir}/10^{14}h_{70}^{-1}M_\odot)^{0.5~0.55}, and a simple self-similar evolution model (T_{gas} \propto M_{vir}^{2/3}) is strongly disfavored. In the cosmological model that we assume (a ΛCDM universe with Ω_0=0.3, λ_0=0.7 and h_{70}=1), the derived mass-temperature relation suggests that the mass fluctuation amplitude σ_8 is 0.7--0.8.

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arXiv2002

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.

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arXiv2001

A New Measurement of the X-ray Temperature Function of Clusters of Galaxies

We present a newly measured X-ray temperature function of galaxy clusters using a complete flux-limited sample of 61 clusters. The sample is constructed with the total survey area of 8.14 steradians and the flux limit of 1.99e-11 ergs/s/cm^2 in the 0.1-2.4keV band. X-ray temperatures and fluxes of the sample clusters were accurately measured with ASCA and ROSAT data. The derived temperature function covers an unprecedentedly wide temperature range of 1.4-11keV. By fitting these data with theoretically predicted temperature functions given by the Press-Schechter formalism together with a recent formation approximation and the CDM power spectrum, we obtained tight and individual constraints on Omega_m,0 and sigma_8. We also employed the Formation-Epoch model in which the distribution in the formation epoch of clusters as well as the temperature evolution are taken into account, showing significantly different results. Systematics caused by the uncertainty in the mass-temperature relation are studied and found to be as large as the statistical errors.

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arXiv2000

CMB anisotropy from spatial correlations of clusters of galaxies

The SZ effect from clusters of galaxies is a dominant source of secondary CMB anisotropy in the low-redshift universe. We present analytic predictions for the CMB power spectrum from massive halos arising from the SZ effect. Since halos are discrete, the power spectrum consists of a Poisson and a correlation term. The latter is always smaller than the former, which is dominated by nearby bright rich clusters. In practice however, those bright clusters are easy to indentify and can thus be subtracted from the map. After this subtraction, the correlation term dominates degree-scale fluctuations over the Poisson term, as the main contribution to the correlation term comes from distant clusters. We find that the correlation term is detectable by Planck experiment. Since the degree scale spectrum is quite insensitive to the highly uncertain core structures of halos, our predictions are robust on these scales. Measuring the correlation term on degree scales thus cleanly probes the clustering of distant halos. This has not been measured yet, mainly because optical and X-ray surveys are not sufficiently sensitive to include such distant clusters and groups. Our analytic predictions are also compared to adiabatic hydrodynamic simulations. The agreement is remarkably good, down to ten arcminutes scales, indicating that our predictions are robust for the Planck experiment. Below ten arcminute scales, where the details of the core structure dominates the power spectrum, our analytic and simulated predictions might fail. In the near future, interferometer and bolometer array experiments will measure the SZ power spectrum down to arcminutes scales, and yield new insight into the physics of the intrahalo medium.

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arXiv2000

Forming Clusters of Galaxies as the Origin of Unidentified GeV Gamma-Ray Sources

Over half of GeV gamma-ray sources observed by the EGRET experiment have not yet been identified as known astronomical objects. There is an isotropic component of such unidentified sources, whose number is about 60 in the whole sky. Here we calculate the expected number of dynamically forming clusters of galaxies emitting gamma-rays by high energy electrons accelerated in the shock wave when they form, in the framework of the standard theory of structure formation. We find that a few tens of such forming clusters should be detectable by EGRET and hence a considerable fraction of the isotropic unidentified sources can be accounted for, if about 5% of the shock energy is going into electron acceleration. We argue that these clusters are very difficult to detect in x-ray or optical surveys compared with the conventional clusters, because of their extended angular size of about 1 degree. Hence they define a new population of ``gamma-ray clusters''. If this hypothesis is true, the next generation gamma-ray telescopes such as GLAST will detect more than a few thousands of gamma-ray clusters. It would provide a new tracer of dynamically evolving structures in the universe, in contrast to the x-ray clusters as a tracer of hydrodynamically stabilized systems. We also derive the strength of magnetic field required for the extragalactic gamma-ray background by structure formation to extend up to 100 GeV as observed, that is about 10^{-5} of the shock-heated baryon energy density.

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arXiv2000

Substructures revealed by the Sunyaev-Zel'dovich effect at 150GHz in the high resolution map of RXJ1347-1145

We report on mapping observations toward the region of the most luminous X-ray cluster RXJ1347-1145 (z=0.45) through the Sunyaev-Zel'dovich effect at 21GHz and 150GHz with the Nobeyama 45-m telescope. While a low angular resolution image at 21GHz (beam-size of 76'') shows a consistent feature with the ROSAT/HRI X-ray image, a higher angular resolution image (13'') at 150GHz reveals complex morphological structures of the cluster region, which cannot be simply described by the spherical isothermal beta-model. If such inhomogeneous morphological features prove to be generic for high redshift clusters, distance measurements to the clusters based on their Sunyaev-Zel'dovich data with low angular resolution imaging should be interpreted with caution.

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arXiv2000

Collapse of Low Mass Clouds in the Presence of UV Radiation Field

The collapse of marginally Jeans unstable primordial gas clouds in the presence of UV radiation field is discussed. Assuming that the dynamical collapse proceeds approximately in an isothermal self-similar fashion, we investigate the thermal evolution of collapsing central core until H$_2$ cooling dominates photoheating and the temperature drops to below $10^4$K. Consequently, the mass of the cooled core is evaluated as $M_{cool}=3.6\times 10^6 M_\odot(I_{21}/1)^{-0.32}$. This scale depends only on the incident UV intensity, and provides a lower limit to the mass of collapsed objects in the UV radiation field.

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arXiv1999

Two-point correlation functions of X-ray selected clusters of galaxies: theoretical predictions for flux-limited surveys

We have developed a model to describe two-point correlation functions of clusters of galaxies in X-ray flux-limited surveys. Our model properly takes account of nonlinear gravitational evolution of mass fluctuations, redshift-space distortion due to linear peculiar velocity field and to finger-of-god, cluster abundance and bias evolution on the basis of the Press -- Schechter theory, the light-cone effect, and the selection function due to the X-ray flux, temperature and luminosity limits. Applying this model in representative cosmological models, we have presented quantitative predictions for X-ray selected samples feasible from the future surveys with the X-ray satellites including Astro-E, Chandra, and XMM. The comparison of these predictions and the observed cluster clustering will place important cosmological constraints which are complementary to the cluster abundance and the cosmic microwave background.

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arXiv1999

Sunyaev - Zel'dovich fluctuations from spatial correlations between clusters of galaxies

We present angular power spectra of the cosmic microwave background radiation anisotropy due to fluctuations of the Sunyaev-Zel'dovich (SZ) effect through clusters of galaxies. A contribution from the correlation among clusters is especially focused on, which has been neglected in the previous analyses. Employing the evolving linear bias factor based on the Press-Schechter formalism, we find that the clustering contribution amounts to 20-30% of the Poissonian one at degree angular scales. If we exclude clusters in the local universe, it even exceeds the Poissonian noise, and makes dominant contribution to the angular power spectrum. As a concrete example, we demonstrate the subtraction of the ROSAT X-ray flux-limited cluster samples. It indicates that we should include the clustering effect in the analysis of the SZ fluctuations. We further find that the degree scale spectra essentially depend upon the normalization of the density fluctuations, i.e., σ_8, and the gas mass fraction of the cluster, rather than the density parameter of the universe and details of cluster evolution models. Our results show that the SZ fluctuations at the degree scale will provide a possible measure of σ_8, while the arc-minute spectra a probe of the cluster evolution. In addition, the clustering spectrum will give us valuable information on the bias at high redshift, if we can detect it by removing X-ray luminous clusters.

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arXiv1999

Formation of Sub-galactic Clouds under UV Background Radiation

The effects of the UV background radiation on the formation of sub-galactic clouds are studied by means of one-dimensional hydrodynamical simulations. The radiative transfer of the ionizing photons due to the absorption by HI, HeI and HeII, neglecting the emission, is explicitly taken into account. We find that the complete suppression of collapse occurs for the clouds with circular velocities typically in the range V_c \sim 15-40 km/s and the 50% reduction in the cooled gas mass with V_c \sim 20-55 km/s. These values depend most sensitively on the collapse epoch of the cloud, the shape of the UV spectrum, and the evolution of the UV intensity. Compared to the optically thin case, previously investigated by Thoul & Weinberg (1996), the absorption of the external UV photon by the intervening medium systematically lowers the above threshold values by ΔV_c \sim 5 km/s. Whether the gas can contract or keeps expanding is roughly determined by the balance between the gravitational force and the thermal pressure gradient when it is maximally exposed to the external UV flux. Based on our simulation results, we discuss a number of implications on galaxy formation, cosmic star formation history, and the observations of quasar absorption lines. In Appendix, we derive analytical formulae for the photoionization coefficients and heating rates, which incorporate the frequency/direction-dependent transfer of external photons.

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arXiv1999

Cosmological Implications of Galaxy Clusters in X-Ray, Millimeter, and Submillimeter Bands

Cosmological implications of clusters of galaxies are discussed with particular attention to their importance in probing the cosmological parameters. More specifically we compute the number counts of clusters of galaxies, Log $N$ -- Log $S$ relation, in X-ray and submm bands on the basis of the Press--Schechter theory. As an important step toward breaking the degeneracy among the viable cosmological models, we observed the most luminous X-ray cluster RXJ1347-1145 in three bands (21 and 43 GHz in the Nobeyama Radio Observatory, Japan, and 350 GHz in the J. C. Maxwell telescope at Mauna Kea, Hawaii). We report on the preliminary results which are in good agreement with the profile of the Sunayev -- Zel'dovich effect predicted on the basis of the previous X-ray observation of the cluster.

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arXiv1999

Submillimeter detection of the Sunyaev -- Zel'dovich effect toward the most luminous X-ray cluster at z=0.45

We report on the detection of the Sunyaev -- Zel'dovich (SZ) signals toward the most luminous X-ray cluster RXJ1347-1145 at Nobeyama Radio Observatory (21 and 43 GHz) and at James Clerk Maxwell Telescope (350 GHz). In particular the latter is the first successful detection of the SZ temperature increment in the submillimeter band which resolved the profile of a cluster of galaxies. Both the observed spectral dependence and the radial profile of the SZ signals are fully consistent with those expected from the X-ray observation of the cluster. The combined analysis of 21GHz and 350GHz data reproduces the temperature and core-radius of the cluster determined with the ROSAT and ASCA satellites when we adopt the slope of the density profile from the X-ray observations. Therefore our present data provide the strongest and most convincing case for the detection of the submillimeter SZ signal from the cluster, as well as in the Rayleigh -- Jeans regime. We also discuss briefly the cosmological implications of the present results.

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arXiv1998

Cosmological Implications of X-ray Clusters of Galaxies

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arXiv1997

Cosmological Implications of Number Counts of Clusters of Galaxies: logN-logS in X-Ray and Submm Bands

We compute the number counts of clusters of galaxies, the logN-logS relation, in several X-ray and submm bands on the basis of the Press-Schechter theory. We pay particular attention to a set of theoretical models which well reproduce the ROSAT 0.5-2 keV band logN-logS, and explore possibilities to further constrain the models from future observations with ASCA and/or at submm bands. The latter is closely related to the European PLANCK mission and the Japanese Large Millimeter and Submillimeter Array (LMSA) project. We exhibit that one can break the degeneracy in an acceptable parameter region on the $Ω_0 - σ_8$ plane by combining the ROSAT logN-logS and the submm number counts. Models which reproduce the ROSAT band logN-logS will have $N(>S) \sim (150-300) (S/10^{-12} erg cm^{-2} s^{-1})^{-1.3}$ str$^{-1}$ at $S > 10^{-12} erg cm^{-2} s^{-1}$ in the ASCA 2-10 keV band, and $N(>S_ν) \sim (10^2-10^4) (S_ν/100 mJy)^{-1.5} str^{-1}$ at $S_ν> 100 mJy$ in the submm (0.85mm) band. The amplitude of the logN-logS is very sensitive to the model parameters in the submm band. We also compute the redshift evolution of the cluster number counts and compare with that of the X-ray brightest Abell-type clusters. The results, although still preliminary, point to low density ($Ω_0\sim 0.3$) universes. The contribution of clusters to the X-ray and submm background radiations is shown to be insignificant in any model compatible with the ROSAT logN-logS.

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arXiv1997

Constraints on the fluctuation amplitude and density parameter from X-ray cluster number counts

We find that the observed log N - log S relation of X-ray clusters can be reproduced remarkably well with a certain range of values for the fluctuation amplitude $σ_8$ and the cosmological density parameter $Ω_0$ in cold dark matter (CDM) universes. The $1σ$ confidence limits on $σ_8$ in the CDM models with $n=1$ and $h = 0.7$ are expressed as $(0.54 \pm 0.02) Ω_0^{-0.35-0.82Ω_0+0.55Ω_0^2}$ ($λ_0=1-Ω_0$) and $(0.54 \pm 0.02) Ω_0^{-0.28-0.91Ω_0+0.68Ω_0^2}$ ($λ_0=0$), where $n$ is the primordial spectral index, and $h$ and $λ_0$ are the dimensionless Hubble and cosmological constants. The errors quoted above indicate the statistical ones from the observed log N - log S only, and the systematic uncertainty from our theoretical modelling of X-ray flux in the best-fit value of $σ_8$ is about 15%. In the case of $n=1$, we find that the CDM models with $(Ω_0,λ_0,h,σ_8) \simeq (0.3,0.7,0.7,1)$ and $(0.45, 0, 0.7, 0.8)$ simultaneously account for the cluster log N - log$S$, X-ray temperature functions, and the normalization from the COBE 4 year data. The derived values assume the observations are without systematic errors, and we discuss in details other theoretical uncertainties which may change the limits on $Ω_0$ and $σ_8$ from the log N - log S relation. We have shown the power of this new approach which will become a strong tool as the observations attain more precision.

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arXiv1996

Semi-analytic predictions for statistical properties of X-ray clusters of galaxies in cold dark matter universes

Temperature and luminosity functions of X-ray clusters are computed semi-analytically, combining a simple model for the cluster gas properties with the distribution functions of halo formation epochs proposed by Lacey & Cole (1993) and Kitayama & Suto (1996). In contrast to several previous approaches which apply the Press--Schechter mass function in a straightforward manner, our method can explicitly take into account the temperature and luminosity evolution of clusters. In order to make quantitative predictions in a specific cosmological context, we adopt cold dark matter (CDM) universes. Assuming the baryon density parameter $Ω_{\rm B}=0.0125 h^{-2}$ ($h$ is the Hubble constant in units of 100 km$\cdot$sec$^{-1}\cdot$Mpc$^{-1}$) and the {\it COBE} normalization of matter fluctuations, temperature and luminosity functions of X-ray clusters depend sensitively on the density parameter $Ω_0$. Allowing for several uncertainties in observational data as well as in our simplified assumptions, we conclude that $Ω_0 \sim 0.2-0.5$ and $h\sim 0.7$ CDM models with/without the cosmological constant reproduce simultaneously the observed temperature and luminosity functions of X-ray clusters at redshift $z\sim0$.

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arXiv1996

Formation rate of gravitational structures and the cosmic X-ray background radiation

Analytical expressions for the rates of formation and destruction of gravitationally bound systems are derived assuming that they are originated from primordial random-Gaussian density fluctuations. The resulting formulae reproduce the time derivative of the Press-Schechter mass function in a certain limit. Combining a theoretical model for the evolution of structures with the formation rate, we can make various cosmological predictions which are to be compared with observations. As an example to elucidate such applicability, we evaluate the contribution of clusters of galaxies to the cosmic X-ray background radiation. With the {\it COBE} normalization, we find that the significant fraction of the observed soft X-ray background is accounted for by clusters of galaxies in a cold dark matter universe with $Ω_0 \sim 0.2$, $λ_0 =1- Ω_0$ and $h \sim 0.8$.

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