Dynamical Masses in Luminous Infrared Galaxies

We have studied the dynamics and masses of a sample of ten nearby luminous and ultraluminous infrared galaxies (LIRGS and ULIRGs), using 2.3 micron CO absorption line spectroscopy and near-infrared H- and Ks-band imaging. By combining velocity dispersions derived from the spectroscopy, disk scale-lengths obtained from the imaging, and a set of likely model density profiles, we calculate dynamical masses for each LIRG. For the majority of the sample, it is difficult to reconcile our mass estimates with the large amounts of gas derived from millimeter observations and from a standard conversion between CO emission and H_2 mass. Our results imply that LIRGs do not have huge amounts of molecular gas (10^10-10^11 Msolar) at their centers, and support previous indications that the standard conversion of CO to H_2 probably overestimates the gas masses and cannot be used in these environments. This in turn suggests much more modest levels of extinction in the near-infrared for LIRGs than previously predicted (A_V~10-20 versus A_V~100-1000). The lower gas mass estimates indicated by our observations imply that the star formation efficiency in these systems is very high and is triggered by cloud-cloud collisions, shocks, and winds rather than by gravitational instabilities in circumnuclear gas disks.Comment: 14 pages, 2 figures, accepted to Ap

Extended Emission Line Gas in Radio Galaxies - PKS0349-27

PKS0349-27 is a classical FRII radio galaxy with an AGN host which has a spectacular, spiral-like structure in its extended emission line gas (EELG). We have measured the velocity field in this gas and find that it splits into 2 cloud groups separated by radial velocities which at some points approach 400 km/s Measurements of the diagnostic emission line ratios [OIII]5007/H-beta, [SII]6716+6731/H-alpha, and [NII]6583/H-alpha in these clouds show no evidence for the type of HII region emission associated with starburst activity in either velocity system. The measured emission line ratios are similar to those found in the nuclei of narrow-line radio galaxies, but the extended ionization/excitation cannot be produced by continuum emission from the active nucleus alone. We present arguments which suggest that the velocity disturbances seen in the EELG are most likely the result of a galaxy-galaxy collision or merger but cannot completely rule out the possibility that the gas has been disrupted by the passage of a radio jet.Comment: 12 pages, 3 fig pages, to appear in the Astrophys.

Minimum Thermal Conductivity of Superlattices

The phonon thermal conductivity of a multilayer is calculated for transport perpendicular to the layers. There is a cross over between particle transport for thick layers to wave transport for thin layers. The calculations shows that the conductivity has a minimum value for a layer thickness somewhat smaller then the mean free path of the phonons.Comment: new results added, to appear in PR

Domain Walls Motion and Resistivity in a Fully-Frustrated Josephson Array

It is identified numerically that the resistivity of a fully-frustrated Josephson-junction array is due to motion of domain walls in vortex lattice rather than to motion of single vortices

A high resolution view of the jet termination shock in a hot spot of the nearby radio galaxy Pictor A: implications for X-ray models of radio galaxy hot spots

Images made with the VLBA have resolved the region in a nearby radio galaxy, Pictor A, where the relativistic jet that originates at the nucleus terminates in an interaction with the intergalactic medium, a so-called radio galaxy hot spot. This image provides the highest spatial resolution view of such an object to date (16 pc), more than three times better than previous VLBI observations of similar objects. The north-west Pictor A hot spot is resolved into a complex set of compact components, seen to coincide with the bright part of the hot spot imaged at arcsecond-scale resolution with the VLA. In addition to a comparison with VLA data, we compare our VLBA results with data from the HST and Chandra telescopes, as well as new Spitzer data. The presence of pc-scale components in the hot spot, identifying regions containing strong shocks in the fluid flow, leads us to explore the suggestion that they represent sites of synchrotron X-ray production, contributing to the integrated X-ray flux of the hot spot, along with X-rays from synchrotron self-Compton scattering. This scenario provides a natural explanation for the radio morphology of the hot spot and its integrated X-ray emission, leading to very different predictions for the higher energy X-ray spectrum compared to previous studies. From the sizes of the individual pc-scale components and their angular spread, we estimate that the jet width at the hot spot is in the range 70 - 700 pc, which is comparable to similar estimates in PKS 2153-69, 3C 205, and 4C 41.17. The lower limit in this range arises from the suggestion that the jet may dither in its direction as it passes through hot spot backflow material close to the jet termination point, creating a "dentist drill" effect on the inside of a cavity 700 pc in diameter.Comment: Accepted by the Astronomical Journal. 35 pages, 6 figure

Chandra LETGS and XMM-Newton observations of NGC 4593

In this paper, we analyze spectra of the Seyfert 1 galaxy NGC 4593 obtained with the Chandra Low Energy Transmission Grating Spectrometer (LETGS), the Reflection Grating Spectrometer (RGS) and the European Photon Imaging Camera's (EPIC) onboard of XMM-Newton. The two observations were separated by ~7 months. In the LETGS spectrum we detect a highly ionized warm absorber corresponding to an ionization state of 400x10^{-9} W m, visible as a depression at 10-18 \AA. This depression is formed by multiple weak Fe and Ne lines. A much smaller column density was found for the lowly ionized warm absorber, corresponding to xi = 3x10^{-9} W m. However, an intermediate ionization warm absorber is not detected. For the RGS data the ionization state is hard to constrain. The EPIC results show a narrow Fe Kalpha line.Comment: 8 pages, 10 figures, accepted for publication in A&

The Kinematics of Thick Disks in External Galaxies

We present kinematic measurements of the thick and thin disks in two edge-on galaxies. We have derived stellar rotation curves at and above the galaxies' midplanes using Ca II triplet features measured with the GMOS spectrograph on Gemini North. In one galaxy, FGC 1415, the kinematics above the plane show clear rotation that lags that of the midplane by ~20-50%, similar to the behavior seen in the Milky Way. However, the kinematics of the second galaxy, FGC 227, are quite different. The rotation above the plane is extremely slow, showing <25% of the rotation speed of the stars at the midplane. We decompose the observed rotation curves into a superposition of thick and thin disk kinematics, using 2-dimensional fits to the galaxy images to determine the fraction of thick disk stars at each position. We find that the thick disk of FGC 1415 rotates at 30-40% of the rotation speed of the thin disk. In contrast, the thick disk of FGC 227 is very likely counter-rotating, if it is rotating at all. These observations are consistent with the velocity dispersion profiles we measure for each galaxy. The detection of counter-rotating thick disks conclusively rules out models where the thick disk forms either during monolithic collapse or from vertical heating of a previous thin disk. Instead, the data strongly support models where the thick disk forms from direct accretion of stars from infalling satellites.Comment: 13 pages, 10 figures. Accepted for publication in Ap

A quantitative analysis of measures of quality in science

Condensing the work of any academic scientist into a one-dimensional measure of scientific quality is a difficult problem. Here, we employ Bayesian statistics to analyze several different measures of quality. Specifically, we determine each measure's ability to discriminate between scientific authors. Using scaling arguments, we demonstrate that the best of these measures require approximately 50 papers to draw conclusions regarding long term scientific performance with usefully small statistical uncertainties. Further, the approach described here permits the value-free (i.e., statistical) comparison of scientists working in distinct areas of science.Comment: 11 pages, 8 figures, 4 table

Mean Field Theory of Josephson Junction Arrays with Charge Frustration

Using the path integral approach, we provide an explicit derivation of the equation for the phase boundary for quantum Josephson junction arrays with offset charges and non-diagonal capacitance matrix. For the model with nearest neighbor capacitance matrix and uniform offset charge $q/2e=1/2$, we determine, in the low critical temperature expansion, the most relevant contributions to the equation for the phase boundary. We explicitly construct the charge distributions on the lattice corresponding to the lowest energies. We find a reentrant behavior even with a short ranged interaction. A merit of the path integral approach is that it allows to provide an elegant derivation of the Ginzburg-Landau free energy for a general model with charge frustration and non-diagonal capacitance matrix. The partition function factorizes as a product of a topological term, depending only on a set of integers, and a non-topological one, which is explicitly evaluated.Comment: LaTex, 24 pages, 8 figure