Li-Zhi Fang

The LX-T and LX-σ Relationships for Galaxy Clusters Revisited

The relationships between the X-ray-determined bolometric luminosity, LX, the temperature, T, of the intracluster gas, and the optical measured velocity dispersion, σ, of the cluster galaxies are updated for galaxy clusters using the largest sample of 256 clusters drawn from literature. The newly established relationships, based on the doubly weighted orthogonal distance regression (ODR) method, are justified by both their self-consistency and co-consistency, which can then be used to test the theoretical models of cluster formation and evolution. The observationally determined LX-T and LX-σ relationships, LX ∝ T2.72±0.05 ∝ σ5.24±0.29, are marginally consistent with those predicted by the scenario in which both intracluster gas and galaxies are in isothermal and hydrostatic equilibrium with the underlying gravitational potential of clusters. A comparison between these observed and predicted LX-T relationships also suggests that the mean cluster baryon fraction, fb, remains approximately constant among different clusters, fb ≈ 0.17, which gives rise to a low mass density universe of Ωm ≈ 0.3.

EVIDENCE FOR SCALE-SCALE CORRELATIONS IN THE COSMIC MICROWAVE BACKGROUND RADIATION

We perform a discrete wavelet analysis of the Cosmic Background Explorer differential microwave radiometer (DMR) 4-yr sky maps and find a significant scale-scale correlation on angular scales from about 11\ifmmode^\circ\else\textdegree\fi{} to 22\ifmmode^\circ\else\textdegree\fi{}, only in the DMR face centered on the north galactic pole. This non-Gaussian signature does not arise either from the known foregrounds or the correlated noise maps, nor is it consistent with upper limits on the residual systematic errors in the DMR maps. Either the scale-scale correlations are caused by an unknown foreground contaminate or systematic errors on angular scales as large as 22\ifmmode^\circ\else\textdegree\fi{}, or the standard inflation plus cold dark matter paradigm is ruled out at the

Steps toward determination of the size and structure of the broad-line region in active galactic nuclei. XII. Ground-based monitoring of 3C 390.3

g99%

A comparison of different cluster mass estimates: consistency or discrepancy?

confidence level.

A Statistical Comparison of Cluster Mass Estimates from Optical/X-Ray Observations and Gravitational Lensing

Results of a ground-based optical monitoring campaign on 3C 390.3 in 1994-1995 are presented. The broadband fluxes (B, V, R, and I), the spectrophotometric optical continuum flux Fλ(5177 A), and the integrated emission-line fluxes of Hα, Hβ, Hγ, He I λ5876, and He II λ4686 all show a nearly monotonic increase with episodes of milder short-term variations superposed. The amplitude of the continuum variations increases with decreasing wavelength (4400-9000 A). The optical continuum variations follow the variations in the ultraviolet and X-ray with time delays, measured from the centroids of the cross-correlation functions, typically around 5 days, but with uncertainties also typically around 5 days; zero time delay between the high-energy and low-energy continuum variations cannot be ruled out. The strong optical emission lines Hα, Hβ, Hγ, and He I λ5876 respond to the high-energy continuum variations with time delays typically about 20 days, with uncertainties of about 8 days. There is some evidence that He II λ4686 responds somewhat more rapidly, with a time delay of around 10 days, but again, the uncertainties are quite large (~8 days). The mean and rms spectra of the Hα and Hβ line profiles provide indications for the existence of at least three distinct components located at ±4000 and 0 km s-1 relative to the line peak. The emission-line profile variations are largest near line center.

Substructures and density profiles of clusters in models of galaxy formation

Rich and massive clusters of galaxies at intermediate redshift are capable of magnifying and distorting the images of background galaxies. A comparison of different mass estimators among these clusters can provide useful information about the distribution and composition of cluster matter and its dynamical evolution. Using the hitherto largest sample of lensing clusters drawn from the literature, we compare the gravitating masses of clusters derived from the strong/weak gravitational lensing phenomena, from the X-ray measurements based on the assumption of hydrostatic equilibrium, and from the conventional isothermal sphere model for the dark matter profile characterized by the velocity dispersion and core radius of galaxy distributions in clusters. While there is excellent agreement between the weak lensing, X-ray and isothermal sphere model-determined cluster masses, these methods are likely to underestimate the gravitating masses enclosed within the central cores of clusters by a factor of 2–4 as compared with the strong lensing results. Such a mass discrepancy has probably arisen from the inappropriate applications of the weak lensing technique and the hydrostatic equilibrium hypothesis to the central regions of clusters, as well as from assuming an unreasonably large core radius for both luminous and dark matter profiles. Nevertheless, it is pointed out that these cluster mass estimators may be safely applied on scales greater than the core sizes. Namely, the overall clusters of galaxies at intermediate redshift can still be regarded as the dynamically relaxed systems, in which the velocity dispersion of galaxies and the temperature of X-ray emitting gas are good indicators of the underlying gravitational potentials of clusters.

Non-Gaussianity and the Recovery of the Mass Power Spectrum from the Lyα Forest

We present a statistical comparison of three different estimates of cluster mass, namely, the dynamical masses obtained from the velocity dispersion of optical galaxies, the X-ray masses measured from the temperature of X-ray-emitting gas under the assumption of isothermal hydrostatic equilibrium, and the gravitational lensing masses derived from the strong/weak distortions of background galaxy images. Using a sample of 29 lensing clusters available in literature, we show that the dynamical masses are in agreement with the gravitational lensing masses while the X-ray method has systematically underestimated cluster masses by a factor of 2-3 as compared with the others. These results imply that galaxies indeed trace the gravitational potential of their clusters and that there is no bias between the velocities of the dark matter particles and the galaxies in clusters. The X-ray cluster mass discrepancy probably arises from the simplification in the models for the X-ray gas distribution and dynamical evolution.

VORTICITY OF INTERGALACTIC MEDIUM VELOCITY FIELD ON LARGE SCALES

In this paper we investigate, using high resolution N-body simulations, the density profiles and the morphologies of galaxy clusters in seven models of structure formation. We show that these properties of clusters are closely related to the occurrence of a significant merging event in the recent past. The seven models are: (1) the standard CDM model (SCDM) with

MEASURING THE GALAXY POWER SPECTRUM AND SCALE-SCALE CORRELATIONS WITH MULTIRESOLUTION-DECOMPOSED COVARIANCE. I. METHOD

\Omega_0 = 1

A Wavelet Space-Scale Decomposition Analysis of Structures and Evolution of QSO LY alpha Absorption Lines

,