Pre-Heated Isentropic Gas in Groups of Galaxies

We confirm that the standard assumption of isothermal, shock-heated gas in cluster potentials is unable to reproduce the observed X-ray luminosity- temperature relation of groups of galaxies. As an alternative, we construct a physically motivated model for the adiabatic collapse of pre-heated gas into an isothermal potential that improves upon the original work of Kaiser (1991). The luminosity and temperature of the gas is calculated, assuming an appropriate distribution of halo formation times and radiation due to both bremsstrahlung and recombination processes. This model successfully reproduces the slope and dispersion of the luminosity-temperature relation of galaxy groups. We also present calculations of the temperature and luminosity functions for galaxy groups under the prescription of this model. This model makes two strong predictions for haloes with total masses M<10^13 M_sun, which are not yet testable with current data: (1) the gas mass fraction will increase in direct proportion to the halo mass; (2) the gas temperature will be larger than the virial temperature of the mass. The second effect is strong enough that group masses determined from gas temperatures will be overestimated by about an order of magnitude if it is assumed that the gas temperature is the virial temperature. The entropy required to match observations can be obtained by heating the gas at the turnaround time, for example, to about 3 X 10^6 K at z=1, which is too high to be generated by a normal rate of supernova explosions. This model breaks down on the scale of low mass clusters, but this is an acceptable limitation, as we expect accretion shocks to contribute significantly to the entropy of the gas in such objects.Comment: Final, refereed version, accepted by MNRAS. One new figure and several clarifying statements have been added. Uses mn.a4.sty (hacked mn.sty). Also available from http://astrowww.phys.uvic.ca/~balogh/entropy.ps.g

Magnetic and Transport Properties of Fe-Ag granular multilayers

Results of magnetization, magnetotransport and Mossbauer spectroscopy measurements of sequentially evaporated Fe-Ag granular composites are presented. The strong magnetic scattering of the conduction electrons is reflected in the sublinear temperature dependence of the resistance and in the large negative magnetoresistance. The simultaneous analysis of the magnetic properties and the transport behavior suggests a bimodal grain size distribution. A detailed quantitative description of the unusual features observed in the transport properties is given

Color bimodality: Implications for galaxy evolution

We use a sample of 69726 galaxies from the SDSS to study the variation of the bimodal color-magnitude (CM) distribution with environment. Dividing the galaxy population by environment (Sigma_5) and luminosity (-23<M_r<-17), the u-r color functions are modeled using double-Gaussian functions. This enables a deconvolution of the CM distributions into two populations: red and blue sequences. The changes with increasing environmental density can be separated into two effects: a large increase in the fraction of galaxies in the red distribution, and a small color shift in the CM relations of each distribution. The average color shifts are 0.05+-0.01 and 0.11+-0.02 for the red and blue distributions, respectively, over a factor of 100 in projected neighbor density. The red fraction varies between about 0% and 70% for low-luminosity galaxies and between about 50% and 90% for high-luminosity galaxies. This difference is also shown by the variation of the luminosity functions with environment. We demonstrate that the effects of environment and luminosity can be unified. A combined quantity, Sigma_mod = Sigma_5/Mpc^{-2} + L_r/L_{-20.2}, predicts the fraction of red galaxies, which may be related to the probability of transformation events. Our results are consistent with major interactions (mergers and/or harassment) causing galaxies to transform from the blue to the red distribution. We discuss this and other implications for galaxy evolution from earlier results and model the effect of slow transformations on the color functions.Comment: 14 pages, 8 figures, in AIP Conf. Proc., The New Cosmology, eds. R. E. Allen et al. (aka. The Mitchell Symposium), see http://proceedings.aip.org/proceedings/confproceed/743.jsp ; v2: replaced Figure 5 which was incomplete in original submissio

Thermal stability of the microstructure of severely deformed copper

Copper specimens were deformed by equal channel angular pressing (ECAP) up to 8 passes. The microstructure was studied by X-ray line profile analysis. The crystallite size is reduced to a few tens of nanometers even after the first ECAP pass and it does not change significantly during further deformation. At the same time, the dislocation density increases gradually up to 4 ECAP passes. The thermal stability of the microstructure is examined by differential scanning calorimetry (DSC). The temperature of the DSC peak decreases whereas the stored energy increases with increasing strain. At the beginning of the heat release a bimodal grain structure develops indicated by a special double-peak shape of the diffraction line profiles

Wavelet analysis of magnetic turbulence in the Earth's plasma sheet

Recent studies provide evidence for the multi-scale nature of magnetic turbulence in the plasma sheet. Wavelet methods represent modern time series analysis techniques suitable for the description of statistical characteristics of multi-scale turbulence. Cluster FGM (fluxgate magnetometer) magnetic field high-resolution (~67 Hz) measurements are studied during an interval in which the spacecraft are in the plasma sheet. As Cluster passes through different plasma regions, physical processes exhibit non-steady properties on magnetohydrodynamic (MHD) and small, possibly kinetic scales. As a consequence, the implementation of wavelet-based techniques becomes complicated due to the statistically transitory properties of magnetic fluctuations and finite size effects. Using a supervised multi-scale technique which allows existence test of moments, the robustness of higher-order statistics is investigated. On this basis the properties of magnetic turbulence are investigated for changing thickness of the plasma sheet.Comment: 17 pages, 5 figure