Galaxy Modelling -- I. Spectral Energy Distributions from Far-UV to Sub-mm Wavelengths

(abridged) We present STARDUST, a new self-consistent modelling of the spectral energy distributions (SEDs) of galaxies from far-UV to radio wavelengths. In order to derive the SEDs in this broad spectral range, we first couple spectrophotometric and (closed-box) chemical evolutions to account for metallicity effects on the spectra of synthetic stellar populations. We then use a phenomenological fit for the metal-dependent extinction curve and a simple geometric distribution of the dust to compute the optical depth of galaxies and the corresponding obscuration curve. This enables us to calculate the fraction of stellar light reprocessed in the infrared range. In a final step, we define a dust model with various components and we fix the weights of these components in order to reproduce the IRAS correlation of IR colours with total IR luminosities. This allows us to compute far-IR SEDs that phenomenologically mimic observed trends. We are able to predict the spectral evolution of galaxies in a broad wavelength range, and we can reproduce the observed SEDs of local spirals, starbursts, luminous infrared galaxies (LIRGs) and ultra luminous infrared galaxies (ULIRGs). This modelling is so far kept as simple as possible and depends on a small number of free parameters, namely the initial mass function (IMF), star formation rate (SFR) time scale, gas density, and galaxy age, as well as on more refined assumptions on dust properties and the presence (or absence) of gas inflows/outflows.Comment: 20 pages, 23 figures, Accepted for publication in Astronomy and Astrophysics Main Journa

A New Local Temperature Distribution Function for X-ray Clusters: Cosmological Applications

(abridged) We present a new determination of the local temperature function of X-ray clusters. We use a new sample comprising fifty clusters for which temperature information is now available, making it the largest complete sample of its kind. It is therefore expected to significantly improve the estimation of the temperature distribution function of moderately hot clusters. We find that the resulting temperature function is higher than previous estimations, but agrees well with the temperature distribution function inferred from the BCS and RASS luminosity function. We have used this sample to constrain the amplitude of the matter fluctuations on cluster's scale of $8\sqrt[3]{\Omega_0}^{-1}h^{-1}$Mpc, assuming a mass-temperature relation based on recent numerical simulations. We find $\sigma_8 = 0.6\pm 0.02$ for an $\Omega_0 = 1$ model. Our sample provides an ideal reference at $z \sim 0$ to use in the application of the cosmological test based on the evolution of X-ray cluster abundance (Oukbir & Blanchard 1992, 1997). Using Henry's sample, we find that the abundance of clusters at $z = 0.33$ is significantly smaller, by a factor larger than 2, which shows that the EMSS sample provides strong evidence for evolution of the cluster abundance. A likelihood analysis leads to a rather high value of the mean density parameter of the universe: $\Omega =0.92 \pm 0.22$ (open case) and $\Omega =0.86 \pm 0.25$ (flat case), which is consistent with a previous, independent estimation based on the full EMSS sample by Sadat et al.(1998). Some systematic uncertainties which could alter this result are briefly discussed.Comment: 31 pages, 12 figures, mathches the version published in Astronomy and Astrophysic

The mean density of the Universe from cluster evolution

The determination of the mean density of the Universe is a long standing problem of modern cosmology. The number density evolution of x-ray clusters at a fixed temperature is a powerful cosmological test, new in nature (Oukbir and Blanchard, 1992), somewhat different from standard analyses based on the dynamical measurement of individual objects. However, the absence of any available sample of x-ray selected clusters with measured temperatures at high redshift has prevented this test from being applied earlier. Recently, temperature measurements of ten EMSS clusters at $0.3 \le z \le 0.4$ have allowed the application of this test (Henry, 1997). In this work, we present the first results of a new analysis we have performed of this data set as well as a new estimation of the local temperature distribution function of clusters: a likelihood analysis of the temperature distribution functions gives a preferred value for the mean density of the universe which corresponds to 75% of the critical density. An open model with a density smaller than 30% of the critical density is rejected with a level of significance of 95%.Comment: 4 pages, shortened. To be published in Les Comptes Rendus de l'Academie des Science

The Expected Rate of Gamma-Ray Burst Afterglows In Supernova Searches

We predict the rate at which Gamma-Ray Burst (GRB) afterglows should be detected in supernova searches as a function of limiting flux. Although GRB afterglows are rarer than supernovae, they are detectable at greater distances because of their higher intrinsic luminosity. Assuming that GRBs trace the cosmic star formation history and that every GRB gives rise to a bright afterglow, we find that the average detection rate of supernovae and afterglows should be comparable at limiting magnitudes brighter than K=18. The actual rate of afterglows is expected to be somewhat lower since only a fraction of all gamma-ray selected GRBs were observed to have associated afterglows. However, the rate could also be higher if the initial gamma-ray emission from GRB sources is more beamed than their late afterglow emission. Hence, current and future supernova searches can place strong constraints on the afterglow appearance fraction and the initial beaming angle of GRB sources.Comment: 13 pages, submitted to ApJ

Liquefaction Case Histories from 1990 Manjil, Iran, Earthquake

The Manjil, Iran, earthquake caused extensive liquefaction and liquefaction-induced damage to residential, commercial and public structures. This paper presents liquefaction case histories as well as the results from our analysis of the data. Based on the field observations made in Iran, liquefaction strength of clean sands for Ms=7.7 is established. The resulting liquefaction resistance versus density relationship is compared with the results published by Seed et al. (1983)

‘Pulsing’ cities and ‘swarming’ metropolises: A simplified, entropy-based approach to long-term urban development

Relocating activities along the fringe, re-designing economic functions, and re-modelling settlement structures across larger regions and broader spatial scales, reflect the inherent shift toward complex metropolitan systems. A refined understanding of urban change requires the adoption of a ‘complex thinking’ that focuses on adaptive behaviour of key agents and local development networks within highly volatile real estate markets. By linking ecology with regional science, our study investigates speed and spatial direction of building activity rates introducing original indicators of urban growth and an exploratory multivariate statistics of the evolving socioeconomic context in the Athens’ region, Greece. Having experienced spatially uncoordinated growth that often resulted in self-organised settlements and socially diversified neighbourhoods, Athens was a paradigmatic example of complex metropolitan systems in Europe. The empirical findings of our study identify non-linear stages of the metropolitan cycle supporting the assumption that long-term urban expansion is a recursive process, with irregular accelerations and decelerations, and a complex relationship between spatial and temporal dimensions. Urban transformations are associated with a broad spectrum of socioeconomic conditions. While playing a variable role over the last century, the most relevant factors in Athens’ growth include population dynamics, urban concentration, and wealth accumulation. Considering such dynamics, spatial planning is required to give adaptive responses to discontinuous socioeconomic development increasingly dependent on territorial aspects and environmental constraints

Velocity Dispersions of CNOC Clusters and the Evolution of the Cluster Abundance

We present the results of the analysis of the internal velocity dispersions, \sigma_v, for the CNOC sample of distant galaxy clusters, based on an interlopers removal algorithm, which is different from that originally applied by Carlberg et al. (1996, C96). We find that the resulting \sigma_v values are consistent within <10% with the original C96 estimates. This result points in favor of a substantial robustness of currently applied methods for optical studies of the internal cluster dynamics. The resulting distribution of velocity dispersions is used to trace the redshift evolution of the cluster abundance with the aim of constraining the matter density parameter, \Omega_m. We find that constraints on \Omega_m are very sensitive to the adopted value of \sigma_8, as obtainable from the local cluster abundance: as \sigma_8 varies from 0.5 to 0.6 (for Omega_m=1), the best fitting Omega_m varies in the range 0.3-1.0.Comment: 11 pages, 8 figures, 1 table, LateX, uses apj.sty, ApJ, corrected some typo