Journal Staff

Electrical properties and strain gauge factor of Cr/SiOx cermet films with compositions 50/50 and 70/30 wt% were investigated in order to evaluate their use in strain gauge devices. The films were deposited by flash evaporation. The microstructures and resulting phases were characterized by electron diffraction and electron microscopy. The influence of the thickness and deposition rate on the sheet resistance, the temperature coefficient of resistance and the gauge factor were investigated. The results are consistent with a mixed conduction mechanism with metallic and a thermally activated tunneling components, between interconnected and discrete conductive phases, respectively.Se investigaron las propiedades eléctricas y el factor extensométrico de películas del cermet- Cr/SiOx en composiciones 50/50 y 70/30 % en peso, para evaluar su uso en dispositivos "strain gauge". Las películas fueron depositadas por evaporación "flash". Las estructuras y fases resultantes fueron caracterizadas por microscopía y difracción de electrones. Se estudió la influencia del espesor y la velocidad del depósito sobre la resistencia laminar, el coeficiente térmico de resistencia y el factor extensométrico. Los resultados son consistentes con un mecanismo de conducción mixto, con una componente metálica y otra por efecto túnel térmicamente activado, entre fases conductoras interconectadas y discretas, respectivamente

LGBTQ Employee Groups: Who Are They Good For? How Are They Organized?

LGBTQ employees seek workplace change through formal and informal groups. Some groups emphasize broader social change and others focus on organizational performance. We provide the social and historical background of these groups and provide a framework for understanding their goals and aims

Clustering of red Galaxies near the Radio-loud Quasar 1335.8+2834 at z=1.1

We have obtained new deep optical and near-infrared images of the field of the radio-loud quasar 1335.8+2834 at $z=1.086$ where an excess in the surface number density of galaxies was reported by Hutchings et al. [AJ, 106, 1324] from optical data. We found a significant clustering of objects with very red optical-near infrared colors, $4 \lesssim R-K \lesssim 6$ and $3 \lesssim I-K \lesssim 5$ near the quasar. The colors and magnitudes of the reddest objects are consistent with those of old (12 Gyr old at z=0) passively-evolving elliptical galaxies seen at $z=1.1$, clearly defining a `red envelope' like that found in galaxy clusters at similar or lower redshifts. This evidence strongly suggests that the quasar resides in a moderately-rich cluster of galaxies (richness-class $\geq 0$). There is also a relatively large fraction of objects with moderately red colors ($3.5 < R-K < 4.5$) which have a distribution on the sky similar to that of the reddest objects. They may be interpreted as cluster galaxies with some recent or on-going star formation.Comment: 14 pages text, 5 PostScript figures, 1 GIF figure, and 1 combined PS file. Accepted for ApJ, Letter

The Deficit of Distant Galaxy Clusters in the RIXOS X-ray Survey

Clusters of galaxies are the largest gravitationally bound systems and therefore provide an important way of studying the formation and evolution of the large scale structure of the Universe. Cluster evolution can be inferred from observations of the X-ray emission of the gas in distant clusters, but interpreting these data is not straightforward. In a simplified view, clusters grow from perturbations in the matter distribution: their intracluster gas is compressed and shock-heated by the gravitational collapse$^{1}$. The resulting X-ray emission is determined by the hydrostatic equilibrium of the gas in the changing gravitational potential. However, if processes such as radiative cooling or pre-collapse heating of the gas are important, then the X-ray evolution will be strongly influenced by the thermal history of the gas. Here we present the first results from a faint flux-limited sample of X-ray selected clusters compiled as part of the ROSAT International X-ray and Optical Survey (RIXOS). Very few distant clusters have been identified. Most importantly, their redshift distribution appears to be inconsistent with simple models based on the evolution of the gravitational potential. Our results suggest that radiative cooling or non-gravitational heating of the intracluster gas must play an important role in the evolution of clusters.Comment: uuencoded compressed postscript. The preprint is also available at http://www.ast.cam.ac.uk/preprint/PrePrint.htm

Cooling Flow Star Formation and the Apparent Stellar Ages of Elliptical Galaxies

Observational constraints and theoretical arguments indicate that cooled interstellar gas in bright elliptical galaxies forms into a young stellar population throughout the region within the half-light radius. The young population has a bottom-heavy, but optically luminous IMF extending to 1 - 2 M_sun. When the colors and spectral features of this young population are combined with those of the underlying old stellar population, the apparent ages are significantly reduced, similar to the relatively young apparent ages observed in many ellipticals. Galactic mergers are not required to resupply young stars. The sensitivity of continuous star formation to L_B and L_x/L_B is likely to account for the observed spread in apparent ages among elliptical galaxies. Local star formation is accompanied by enhanced stellar H_beta equivalent widths, stronger optical emission lines, enhanced thermal X-ray emission and lower apparent temperatures in the hot gas. The young stars should cause M/L to vary with galactic radius, perturbing the fundamental plane occupied by the old stars.Comment: 6 pages with 2 figures; accepted by Astrophysical Journal Letter

Initial Hubble Diagram Results from the Nearby Supernova Factory

The use of Type Ia supernovae as distance indicators led to the discovery of the accelerating expansion of the universe a decade ago. Now that large second generation surveys have significantly increased the size and quality of the high-redshift sample, the cosmological constraints are limited by the currently available sample of ~50 cosmologically useful nearby supernovae. The Nearby Supernova Factory addresses this problem by discovering nearby supernovae and observing their spectrophotometric time development. Our data sample includes over 2400 spectra from spectral timeseries of 185 supernovae. This talk presents results from a portion of this sample including a Hubble diagram (relative distance vs. redshift) and a description of some analyses using this rich dataset.Comment: Short version of proceedings for ICHEP08, Philadelphia PA, July 2008; see v1 for full-length versio

Iron as a tracer in galaxy clusters and groups

Available X-ray data are collected and organized concerning the iron and gas content of galaxy clusters and groups, together with the optical luminosity, mass and iron abundance of cluster galaxies. Several astrophysical inferences are then drawn, including the evidence for rich clusters having evolved without much baryon exchange with their surrondings, and having experienced very similar star formation histories. Groups are much gas-poor compared to clusters, and appear instead to have shed a major fraction of their original cosmic share of baryons, which indicates that galaxy clusters cannot have formed by assembling groups similar to the present day ones. It is argued that this favors low-$\Omega$ universes, in which the growth of rich clusters is virtually complete at high redshifts. It is also argued that elemental abundance ratios in clusters are nearly solar, which is consistent with a similar proportion of supernovae of Type Ia and Type II having enriched both the solar neghborhood as well clusters as a whole. Much of the iron in clusters appears to reside in the intracluster medium rather than inside galaxies. It appears that the baryon to star conversion in clusters has been nearly as efficient as currently adopted for the universe as a whole. Yet the metallicity of the clusters is $\sim 5$ times higher than the global metallicity adopted for the nearby universe. It is concluded that the intergalactic medium should have a metallicity $\sim 1/3$ solar if stellar nucleosynthesis has proceeded in stars within field galaxies with the same efficiency as in stars within clusters of galaxies.Comment: AASTex Latex, 29 pages, 6 figure

Observing the build-up of the colour-magnitude relation at redshift ~0.8

We analyse the rest-frame (U-V) colour-magnitude relation for 2 clusters at redshift 0.7 and 0.8, drawn from the ESO Distant Cluster Survey. By comparing with the population of red galaxies in the Coma cluster, we show that the high redshift clusters exhibit a deficit of passive faint red galaxies. Our results show that the red-sequence population cannot be explained in terms of a monolithic and synchronous formation scenario. A large fraction of faint passive galaxies in clusters today has moved onto the red sequence relatively recently as a consequence of the fact that their star formation activity has come to an end at z<0.8.Comment: 5 pages, 2 figures, to appear in Proc. of IAU Colloq. 195: "Outskirts of Galaxy Clusters: Intense Life in the Suburbs" -- minor typos correcte

The Evolution of Early-Type Galaxies in Distant Clusters

We present results from an optical-IR photometric study of early-type galaxies in 19 galaxy clusters out to z=0.9. The galaxy sample is selected on the basis of morphologies determined from HST WFPC2 images, and is photometrically defined in the K-band to minimize redshift-dependent selection biases. The optical-IR colors of the early-type cluster galaxies become bluer with increasing redshift in a manner consistent with the passive evolution of an old stellar population formed at an early cosmic epoch. The degree of color evolution is similar for clusters at similar redshift, and does not depend strongly on the optical richness or X-ray luminosity of the cluster, suggesting that the history of early-type galaxies is relatively insensitive to environment. The slope of the color-magnitude relationship shows no significant change out to z=0.9, providing evidence that it arises from a correlation between galaxy mass and metallicity, not age. Finally, the intrinsic scatter in the optical-IR colors is small and nearly constant with redshift, indicating that the majority of giant, early-type galaxies in clusters share a common star formation history, with little perturbation due to uncorrelated episodes of later star formation. Taken together, our results are consistent with models in which most early-type galaxies in rich clusters are old, formed the majority of their stars at high redshift in a well-synchronized fashion, and evolved quiescently thereafter.Comment: 55 pages, 24 figures, uses AASTeX. Accepted for publication in The Astrophysical Journa

Host Galaxy Evolution in Radio-Loud AGN

We investigate the luminosity evolution of the host galaxies of radio-loud AGN through Hubble Space Telescope imaging of 72 BL Lac objects, including new STIS imaging of nine z > 0.6 BL Lacs. With their intrinsically low accretion rates and their strongly beamed jets, BL Lacs provide a unique opportunity to probe host galaxy evolution independent of the biases and ambiguities implicit in quasar studies. We find that the host galaxies of BL Lacs evolve strongly, consistent with passive evolution from a period of active star formation in the range 0.5 <~ z <~ 2.5, and inconsistent with either passive evolution from a high formation redshift or a non-evolving population. This evolution is broadly consistent with that observed in the hosts of other radio-loud AGN, and inconsistent with the flatter luminosity evolution of quiescent early types and radio-quiet hosts. This indicates that active star formation, and hence galaxy interactions, are associated with the formation for radio-loud AGN, and that these host galaxies preferentially accrete less material after their formation epoch than galaxies without powerful radio jets. We discuss possible explanations for the link between merger history and the incidence of a radio jet.Comment: 37 pages, 8 figures, accepted for publication in ApJ, for full PDF incl. figures see http://www.ph.unimelb.edu.au/~modowd/papers/odowdurry2005.pd