Gravitational potential and X-ray luminosities of early-type galaxies observed with XMM-Newton and Chandra

We study dark matter content in early-type galaxies and investigate whether X-ray luminosities of early-type galaxies are determined by the surrounding gravitational potential. We derived gravitational mass profiles of 22 early-type galaxies observed with XMM-Newton and Chandra. Sixteen galaxies show constant or decreasing radial temperature profiles, and their X-ray luminosities are consistent with kinematical energy input from stellar mass loss. The temperature profiles of the other 6 galaxies increase with radius, and their X-ray luminosities are significantly higher. The integrated mass-to-light ratio of each galaxy is constant at that of stars within 0.5-1 r_e, and increases with radius, where r_e is the effective radius of a galaxy. The scatter of the central mass-to-light ratio of galaxies was less in K-band light. At 3r_e, the integrated mass-to-light ratios of galaxies with flat or decreasing temperature profiles are twice the value at 0.5r_e, where the stellar mass dominates, and at 6r_e, these increase to three times the value at 0.5r_e. This feature should reflect common dark and stellar mass distributions in early-type galaxies: Within 3r_e, the mass of dark matter is similar to the stellar mass, while within 6r_e, the former is larger than the latter by a factor of two. By contrast, X-ray luminous galaxies have higher gravitational mass in the outer regions than X-ray faint galaxies. We describe these X-ray luminous galaxies as the central objects of large potential structures; the presence or absence of this potential is the main source of the large scatter in the X-ray luminosity.Comment: 22 pages, 18 figures, 6 tables, accepted for publication in A&

Spin melting and refreezing driven by uniaxial compression on a dipolar hexagonal plate

We investigate freezing characteristics of a finite dipolar hexagonal plate by the Monte Carlo simulation. The hexagonal plate is cut out from a piled triangular lattice of three layers with FCC-like (ABCABC) stacking structure. In the present study an annealing simulation is performed for the dipolar plate uniaxially compressed in the direction of layer-piling. We find spin melting and refreezing driven by the uniaxial compression. Each of the melting and refreezing corresponds one-to-one with a change of the ground states induced by compression. The freezing temperatures of the ground-state orders differ significantly from each other, which gives rise to the spin melting and refreezing of the present interest. We argue that these phenomena are originated by a finite size effect combined with peculiar anisotropic nature of the dipole-dipole interaction.Comment: Proceedings of the Highly Frustrated Magnetism (HFM2006) conference. To appear in a special issue of J. Phys. Condens. Matte

ALMA Temporal Phase Stability and the Effectiveness of Water Vapor Radiometer

Atacama Large Millimeter/submillimeter Array (ALMA) will be the world largest mm/submm interferometer, and currently the Early Science is ongoing, together with the commissioning and science verification (CSV). Here we present a study of the temporal phase stability of the entire ALMA system from antennas to the correlator. We verified the temporal phase stability of ALMA using data, taken during the last two years of CSV activities. The data consist of integrations on strong point sources (i.e., bright quasars) at various frequency bands, and at various baseline lengths (up to 600 m). From the observations of strong quasars for a long time (from a few tens of minutes, up to an hour), we derived the 2-point Allan Standard Deviation after the atmospheric phase correction using the 183 GHz Water Vapor Radiometer (WVR) installed in each 12 m antenna, and confirmed that the phase stability of all the baselines reached the ALMA specification. Since we applied the WVR phase correction to all the data mentioned above, we also studied the effectiveness of the WVR phase correction at various frequencies, baseline lengths, and weather conditions. The phase stability often improves a factor of 2 - 3 after the correction, and sometimes a factor of 7 improvement can be obtained. However, the corrected data still displays an increasing phase fluctuation as a function of baseline length, suggesting that the dry component (e.g., N2 and O2) in the atmosphere also contributes the phase fluctuation in the data, although the imperfection of the WVR phase correction cannot be ruled out at this moment.Comment: Proc. SPIE 8444-125, in press (7 pages, 4 figures, 1 table

Staggered magnetism in LiV2_2O4_4 at low temperatures probed by the muon Knight shift

We report on the muon Knight shift measurement in single crystals of LiV2O4. Contrary to what is anticipated for the heavy-fermion state based on the Kondo mechanism, the presence of inhomogeneous local magnetic moments is demonstrated by the broad distribution of the Knight shift at temperatures well below the presumed "Kondo temperature" ($T^*\simeq 30$ K). Moreover, a significant fraction ($\simeq10$ %) of the specimen gives rise to a second component which is virtually non-magnetic. These observations strongly suggest that the anomalous properties of LiV2O4 originates from frustration of local magnetic moments.Comment: 11 pages, 5 figures, sbmitted to J. Phys.: Cond. Mat

Ordered magnetic and quadrupolar states under hydrostatic pressure in orthorhombic PrCu2

We report magnetic susceptibility and electrical resistivity measurements on single-crystalline PrCu2 under hydrostatic pressure, up to 2 GPa, which pressure range covers the pressure-induced Van Vleck paramagnet-to-antiferromagnet transition at 1.2 GPa. The measured anisotropy in the susceptibility shows that in the pressure-induced magnetic state the ordered 4f-moments lie in the ac-plane. We propose that remarkable pressure effects on the susceptibility and resistivity are due to changes in the quadrupolar state of O22 and/or O20 under pressure. We present a simple analysis in terms of the singlet-singlet model.Comment: 14 pages, 9 figures submitted to Phys. Rev.

A spinor approach to Walker geometry

A four-dimensional Walker geometry is a four-dimensional manifold M with a neutral metric g and a parallel distribution of totally null two-planes. This distribution has a natural characterization as a projective spinor field subject to a certain constraint. Spinors therefore provide a natural tool for studying Walker geometry, which we exploit to draw together several themes in recent explicit studies of Walker geometry and in other work of Dunajski (2002) and Plebanski (1975) in which Walker geometry is implicit. In addition to studying local Walker geometry, we address a global question raised by the use of spinors.Comment: 41 pages. Typos which persisted into published version corrected, notably at (2.15

SMA/PdBI multiple line observations of the nearby Seyfert2 galaxy NGC 1068: Shock related gas kinematics and heating in the central 100pc?

We present high angular resolution (0.5-2.0") observations of the mm continuum and the 12CO(J=3-2), 13CO(J=3-2), 13CO(J=2-1), C18O(J=2-1), HCN(J=3-2), HCO+(J=4-3) and HCO+(J=3-2) line emission in the circumnuclear disk (r=100pc) of the proto-typical Seyfert type-2 galaxy NGC1068, carried out with the Submillimeter Array. We further include in our analysis new 13CO(J=1-0) and improved 12CO(J=2-1) observations of NGC1068 at high angular resolution (1.0-2.0") and sensitivity, conducted with the IRAM Plateau de Bure Interferometer. Based on the complex dynamics of the molecular gas emission indicating non-circular motions in the central ~100pc, we propose a scenario in which part of the molecular gas in the circumnuclear disk of NGC1068 is radially blown outwards as a result of shocks. This shock scenario is further supported by quite warm (Tkin>=200K) and dense (nH2=10^4cm^-3) gas constrained from the observed molecular line ratios. The HCN abundance in the circumnuclear disk is found to be [HCN]/[12CO]=10^-3.5. This is slightly higher than the abundances derived for galactic and extragalactic starforming/starbursting regions. This results lends further support to X-ray enhanced HCN formation in the circumnuclear disk of NGC1068, as suggested by earlier studies. The HCO+ abundance ([HCO+]/[12CO]=10^-5) appears to be somewhat lower than that of galactic and extragalactic starforming/starbursting regions. When trying to fit the cm to mm continuum emission by different thermal and non-thermal processes, it appears that electron-scattered synchrotron emission yields the best results while thermal free-free emission seems to over-predict the mm continuum emission.Comment: accepted for publication by ApJ; 35pages, 22 figures and 6 tables (at the end of the file); 3 figures have been decreased in quality to match size limi