Distant radio galaxies in the near IR

We are carrying out a program of near IR imaging and spectroscopy of radio galaxies with redshifts of 1.5 and greater. One of its principal goals is to constrain the ages and star formation histories of massive galaxies at early epochs. The radio galaxies are drawn from the survey of 1Jy class sources by McCarthy et al (1989) and McCarthy (1990). The sample contains 18 radio galaxies with redshifts greater than 2 and an additional 10 objects with 1.5 less than z less than 2.0. The redshifts were obtained from long slit spectra with the CTIO 4 m. While the galaxies are quite faint (r approximately = 21-24.5) all have Lyman alpha emission with rest frame equivalent widths of 100 - 1000 A. Multicolor photometry in the g,r,i and J,H,K bands has been obtained with the 2.5-m Du Pont Telescope on Las Campanas and with the Hale 5 m telescope at Palomar. We have recently obtained near IR spectra, using the 4 m telescopes at KPNO and CTIO, of a few objects with the goal of determining the Lyman alpha/H-alpha ratio and hence the reddening

Extremely red objects in the fields of high redshift radio galaxies

We are engaged in a program of infrared imaging photometry of high redshift radio galaxies. The observations are being done using NICMOS2 and NICMOS3 arrays on the DuPont 100-inch telescope at Las Campanas Observatory. In addition, Persson and Matthews are measuring the spectral energy distributions of normal cluster galaxies in the redshift range 0 to 1. These measurements are being done with a 58 x 62 InSb array on the Palomar 5-m telescope. During the course of these observations we have imaged roughly 20 square arcminutes of sky to limiting magnitudes greater than 20 in the J, H, and K passbands (3 sigma in 3 square arcseconds). We have detected several relatively bright, extremely red, extended objects during the course of this work. Because the radio galaxy program requires Thuan-Gunn gri photometry, we are able to construct rough photometric energy distributions for many of the objects. A sample of the galaxy magnitudes within 4 arcseconds diameter is given. All the detections are real; either the objects show up at several wavelengths, or in subsets of the data. The reddest object in the table, 9ab'B' was found in a field of galaxies in a rich cluster at z = 0.4; 9ab'A' lies 8 arcseconds from it

Non-Perturbative Theory of Dispersion Interactions

Some open questions exist with fluctuation-induced forces between extended dipoles. Conventional intuition derives from large-separation perturbative approximations to dispersion force theory. Here we present a full non-perturbative theory. In addition we discuss how one can take into account finite dipole size corrections. It is of fundamental value to investigate the limits of validity of the perturbative dispersion force theory.Comment: 9 pages, no figure

Whispering gallery modes in open quantum billiards

The poles of the S-matrix and the wave functions of open 2D quantum billiards with convex boundary of different shape are calculated by the method of complex scaling. Two leads are attached to the cavities. The conductance of the cavities is calculated at energies with one, two and three open channels in each lead. Bands of overlapping resonance states appear which are localized along the convex boundary of the cavities and contribute coherently to the conductance. These bands correspond to the whispering gallery modes appearing in the classical calculations.Comment: 9 pages, 3 figures in jpg and gif forma

Constraining the Nature of the Galactic Center X-ray Source Population

We searched for infrared counterparts to the cluster of X-ray point sources discovered by Chandra in the Galactic Center Region (GCR). While the sources could be white dwarfs, neutron stars, or black holes accreting from stellar companions, their X-ray properties are consistent with magnetic Cataclysmic Variables, or High Mass X-ray Binaries (HMXB) at low accretion-rates. A direct way to decide between these possibilities and hence between alternative formation scenarios is to measure or constrain the luminosity distribution of the companions. Using infrared (J, H, K, Br-gamma) imaging, we searched for counterparts corresponding to typical HMXB secondaries: spectral type B0V with K<15 at the GCR. We found no significant excess of bright stars in Chandra error circles, indicating that HMXBs are not the dominant X-ray source population, and account for fewer than 10% of the hardest X-ray sources.Comment: 4 pages, 3 figures, 1 table, accepted in ApJ Letters for publicatio

Elastic contact between self-affine surfaces: Comparison of numerical stress and contact correlation functions with analytic predictions

Contact between an elastic manifold and a rigid substrate with a self-affine fractal surface is reinvestigated with Green's function molecular dynamics. Stress and contact autocorrelation functions (ACFs) are found to decrease algebraically. A rationale is provided for the observed similarity in the exponents for stress and contact ACFs. Both exponents differ substantially from analytic predictions over the range of Hurst roughness exponents studied. The effect of increasing the range of interactions from a hard sphere repulsion to exponential decay is analyzed. Results for exponential interactions are accurately described by recent systematic corrections to Persson's contact mechanics theory. The relation between the area of simply connected contact patches and the normal force is also studied. Below a threshold size the contact area and force are consistent with Hertzian contact mechanics, while area and force are linearly related in larger contact patches.Comment: 12 pages, 9 figure

The rings of Uranus: Results of the 10 April 1978 occultation

Observations of the 10 April 1978 stellar occultation by the rings of Uranus are presented. Nine rings were observed and their radii and widths are calculated. Rings η,y, and δ are found to be most likely circular and coplanar, in agreement with previous analyses; the remaining rings are either noncircular or slightly inclined. The width of the є ring is a linear function of its radius from the center of Uranus, projected onto the satellites' orbital plane; this suggests that it forms one continuous noncircular ring. The optical depth profile of the є ring has not changed significantly since March 1977. A model of this ring which fits all available observations adequately is that of a uniformly precessing Keplerian ellipse coplanar with the satellites' orbits. This model permits predictions of the radius and width of the є ring for future occultations. The precession rate is used to determine J_2 for Uranus, on the assumption that precession is caused solely by the planetary oblateness and not by satellite-ring interactions

Transverse thermal depinning and nonlinear sliding friction of an adsorbed monolayer

We study the response of an adsorbed monolayer under a driving force as a model of sliding friction phenomena between two crystalline surfaces with a boundary lubrication layer. Using Langevin-dynamics simulation, we determine the nonlinear response in the direction transverse to a high symmetry direction along which the layer is already sliding. We find that below a finite transition temperature, there exist a critical depinning force and hysteresis effects in the transverse response in the dynamical state when the adlayer is sliding smoothly along the longitudinal direction.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Let

Dynamical transitions and sliding friction in the two-dimensional Frenkel-Kontorova model

The nonlinear response of an adsorbed layer on a periodic substrate to an external force is studied via a two dimensional uniaxial Frenkel-Kontorova model. The nonequlibrium properties of the model are simulated by Brownian molecular dynamics. Dynamical phase transitions between pinned solid, sliding commensurate and incommensurate solids and hysteresis effects are found that are qualitatively similar to the results for a Lennard-Jones model, thus demonstrating the universal nature of these features.Comment: 11 pages, 12 figures, to appear in Phys. Rev.

Spring flood induced shifts in Fe speciation and fate at increased salinity

Rivers have traditionally been viewed as negligible sources of iron (Fe) to marine waters, as most Fe gets lost during estuarine mixing. However, recent findings demonstrate that Fe from boreal rivers display a higher resistance towards salinity-induced aggregation, presumably due to stabilizing interactions with organic matter. Previous studies have shown that Fe (oxy)hydroxides are selectively removed by aggregation processes, and that organic Fe complexes are less affected by increasing salinity. It has been further proposed that Fe speciation varies in response to seasonal differences in hydrology. In this study X-ray absorption spectroscopy (XAS) was used to determine the temporal variation in Fe speciation and the connection to Fe stability in response to increasing salinity in two boreal rivers (Kalix and Råne River), with the purpose to better understand the fate of riverine Fe export. Sampling was done from winter pre-flood, over the spring flood, to post-flood conditions (early April until mid June). In addition, parallel analyses for Fe speciation and isotope composition (δ56Fe relative to IRMM-14) were made on river samples, as well as salinity-induced aggregates and the fraction remaining in suspension, with the main objective to test if δ56Fe reflect the speciation of Fe. The contribution of organically complexed Fe increased during spring flood compared to the pre- and post-flood, as did Fe transport capacity. However, since Fe (oxy)hydroxides were dominating throughout the sampling period, the seasonal variability was small. Interestingly, salinity-induced aggregation experiments revealed that Fe (oxy)hydroxides, which dominated aggregates, displayed lower δ56Fe than in the river samples Fe, while organic Fe complexes in suspension had higher δ56Fe values. The seasonal variability in Fe isotope signature could not be simply linked to Fe speciation, but was probably also influenced by variation in source areas of Fe and processes along the flow-path that alter both Fe speciation and isotopic composition