Dark Energy and the Hubble Age

I point out that an effective upper limit of approximately 20 Gyr (for a Hubble constant of 72 km/s/Mpc) or alternatively on the $H_0$-independent quantity $H_0t_0 < 1.47$, exists on the age of the Universe, essentially independent of the unknown equation of state of the dominant dark energy component in the Universe. Unless astrophysical constraints on the age of the Universe can convincingly reduce the upper limit to below this value no useful lower limit on the equation of state parameter $w$ for this component can be obtained. Direct dating by stars does not provide a useful constraint, but model-dependent cosmological limits from supernovae and the CMB observations may. For a constant value of $w$, a bound $H_0t_0 -1.5$Comment: 4 pages, submitted to Ap. J. Lett (analytic asymptotic upper bound now added

Confusion of Diffuse Objects in the X-ray Sky

Most of the baryons in the present-day universe are thought to reside in intergalactic space at temperatures of 10^5-10^7 K. X-ray emission from these baryons contributes a modest (~10%) fraction of the ~ 1 keV background whose prominence within the large-scale cosmic web depends on the amount of non-gravitational energy injected into intergalactic space by supernovae and AGNs. Here we show that the virialized regions of groups and clusters cover over a third of the sky, creating a source-confusion problem that may hinder X-ray searches for individual intercluster filaments and contaminate observations of distant groups.Comment: accepted to ApJ Letters, 7 pages, 3 figure

A Comparison of Cosmological Hydrodynamic Codes

We present a detailed comparison of the simulation results of various cosmological hydrodynamic codes. Starting with identical initial conditions based on the Cold Dark Matter scenario for the growth of structure, we integrate from redshift $z=20$ to $z=0$ to determine the physical state within a representative volume of size $L^3$ where $L=64 h^{-1} {\rm Mpc}$. Five independent codes are compared: three of them Eulerian mesh based and two variants of the Smooth Particle Hydrodynamics "SPH" Lagrangian approach. The Eulerian codes were run at $N^3=(32^3,~64^3,~128^3,~{\rm and},~256^3)$ cells, the SPH codes at $N^3= 32^3$ and $64^3$ particles. Results were then rebinned to a $16^3$ grid with the expectation that the rebinned data should converge, by all techniques, to a common and correct result as $N \rightarrow \infty$. We find that global averages of various physical quantities do, as expected, tend to converge in the rebinned model, but that uncertainties in even primitive quantities such as $\langle T \rangle$, $\langle \rho^2\rangle^{1/2}$ persists at the 3\%-17\% level after completion of very large simulations. The two SPH codes and the two shock capturing Eulerian codes achieve comparable and satisfactory accuracy for comparable computer time in their treatment of the high density, high temperature regions as measured in the rebinned data; the variance among the five codes (at highest resolution) for the mean temperature (as weighted by $\rho^2$) is only 4.5\%. Overall the comparison allows us to better estimate errors, it points to ways of improving this current generation of hydrodynamic codes and of suiting their use to problems which exploit their individually best features.Comment: 20p plaintex to appear in The Astrophysical Journal on July 20, 199

Optimizing Observational Strategy for Future Fgas Constraints

The Planck cluster catalog is expected to contain of order a thousand galaxy clusters, both newly discovered and previously known, detected through the Sunyaev-Zeldovich effect over the redshift range 0 < z < 1. Follow-up X-ray observations of a dynamically relaxed sub-sample of newly discovered Planck clusters will improve constraints on the dark energy equation-of-state found through measurement of the cluster gas mass fraction fgas. In view of follow-up campaigns with XMM-Newton and Chandra, we determine the optimal redshift distribution of a cluster sample to most tightly constrain the dark energy equation of state. The distribution is non-trivial even for the standard w0-wa parameterization. We then determine how much the combination of expected data from the Planck satellite and fgas data will be able to constrain the dark energy equation-of-state. Our analysis employs a Markov Chain Monte Carlo method as well as a Fisher Matrix analysis. We find that these upcoming data will be able to improve the figure-of-merit by at least a factor two.Comment: 11 pages, 8 figure

The X-ray Size-Temperature Relation for Intermediate Redshift Galaxy Clusters

We present the first measurements of the X-ray size-temperature (ST) relation in intermediate redshift (z~0.30) galaxy clusters. We interpret the local ST relation (z~0.06) in terms of underlying scaling relations in the cluster dark matter properties, and then we use standard models for the redshift evolution of those dark matter properties to show that the ST relation does not evolve with redshift. We then use ROSAT HRI observations of 11 clusters to examine the intermediate redshift ST relation; for currently favored cosmological parameters, the intermediate redshift ST relation is consistent with that of local clusters. Finally, we use the ST relation and our evolution model to measure angular diameter distances; with these 11 distances we evaluate constraints on Omega_M and Omega_L which are consistent with those derived from studies of Type Ia supernovae. The data rule out a model with Omega_M=1 and Omega_L=0 with 2.5 sigma confidence. When limited to models where Omega_M+Omega_L=1, these data are inconsistent with Omega_M=1 with 3 sigma confidence.Comment: ApJ: submitted April 7, accepted June 28, to appear Dec 1 (vol 544

CURRENT THERAPEUTIC APPROACH OF THE WHITE SPONGE NAEVUS OF THE ORAL CAVITY.

We report a case of White Sponge Naevus of the tongue in a 50 years-old man. White Sponge Naevus of the oral cavity is a rare, benign and dominant autosomic inherited disorder, which presents in the form of a white, hyperplasic and verrucous or spongious lesion of the oral mucosa. Differential diagnosis is clinically difficult with more common white lesions of the oral cavity. Various therapeutic approaches have been proposed. Systemic antibiotics or local applications of retinoic acid provide limited benefits but are poorly effective. To our knowledge, CO2 Laser has never been tried to treat a White Sponge Naevus of the oral cavity. We performed a complete removal of the lesion with CO2 Laser, but complete recurrence occurred. Finally, a surgical resection was realized, which proved to be effective. Two years later, the patient is free of recurrence. This article proposes a review of the literature on what is known on White Sponge Naevus of the oral mucosa. We stress the importance of confrontation between anamnesis, clinical examination and pathologic findings to lead to the proper diagnosis of this rare disease

Accuracy of Mesh Based Cosmological Hydrocodes: Tests and Corrections

We perform a variety of tests to determine the numerical resolution of the cosmological TVD eulerian code developed by Ryu et al (1993). Tests include 512^3 and 256^3 simulations of a Pk=k^{-1} spectrum to check for self-similarity and comparison of results with those from higher resolution SPH and grid-based calculations (Frenk et al 1998). We conclude that in regions where density gradients are not produced by shocks the code degrades resolution with a Gaussian smoothing (radius) length of 1.7 cells. At shock caused gradients (for which the code was designed) the smoothing length is 1.1 cells. Finally, for \beta model fit clusters, we can approximately correct numerical resolution by the transformation R^2_{core}\to R^2_{core}-(C\Delta l)^2, where \Delta l is the cell size and C=1.1-1.7. When we use these corrections on our previously published computations for the SCDM and \Lambda CDM models we find luminosity weighted, zero redshift, X-ray cluster core radii of (210\pm 86, 280\pm 67)h^{-1}kpc, respectively, which are marginally consistent with observed (Jones & Forman 1992) values of 50-200h^{-1}kpc. Using the corrected core radii, the COBE normalized SCDM model predicts the number of bright L_x>10^{43}erg/s clusters too high by a factor of \sim 20 and the \Lambda CDM model is consistent with observations.Comment: ApJ in press (1999

Galaxy clusters - Well of darkness

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62854/1/394122a0.pd