Implicancias cosmológicas de la tectónica de placas

Muy frecuentemente, los avances en nuestra comprensión de la naturale za de las cosas acaban revelándonos que nuestras más enraizadas creencias resultan ser meras convenciones. La idea de relacionar la intensidad de la interacción gravitatoria con el número de partículas en el universo, data de la década del 30 y se debe independientemente a Eddington y Dirac. Dado que el número de partículas decrece a medida que la expansión del universo lleva las partículas más allá del límite de interacción impuesto por la velocidad finita de la luz más rápidamente de lo que otras nuevas son creadas, la intensidad de la constante de interacción decrece. Este hecho es de interés para los geofísicos pues podría permitir la resolución de algunas dificultades que se presentan en la comprensión del mecanismo motriz de la tectónica de placas. Los progresos que las Ciencias de la Tierra pudieren hacer en este sentido, son decisivos para la validación de ciertas teorías cosmológicas.Very frequently the advances in our comprehension of the nature of things show us that our more deeply rooted beliefs are mere conventions. The idea of relating the intensity of the gravitational interaction with the number of particles in the Universe arised already in the 30’s and is due independently to Eddington and Dirac. Since the number of particles di minishes as the expansion of the Universe carries them beyond the interaction limit imposed by the finite light speed, and that happens faster than the replenishment of new particles, the intensity of the interaction constant also diminishes. This fact is of the interest of the geophysicists be cause it could help to solve some of the difficulties that arise in the com prehension of the driving mechanism of plate tectonics. The advances that the Earth Sciences could make at this respect, are decisive to validate so me cosmological theories.Asociación Argentina de Geofísicos y Geodesta

The Stellar Content of the Polar Rings in the Galaxies NGC 2685 and NGC 4650A

We present the results of stellar photometry of polar-ring galaxies NGC 2685 and NGC 4650A, using the archival data obtained with the Hubble Space Telescope's Wide Field Planetary Camera 2. Polar rings of these galaxies were resolved into ~800 and ~430 stellar objects in the B, V and Ic bands, considerable part of which are blue supergiants located in the young stellar complexes. The stellar features in the CM-diagrams are best represented by isochrones with metallicity Z = 0.008. The process of star formation in the polar rings of both galaxies was continuous and the age of the youngest detected stars is about 9 Myr for NGC 2685 and 6.5 Myr for NGC 4650A.Comment: 21 pages, 9 figures, AJ 2004 February, accepte

Formation of central massive objects via tidal compression

For a density that is not too sharply peaked towards the center, the local tidal field becomes compressive in all three directions. Available gas can then collapse and form a cluster of stars in the center, including or even being dominated by a central black hole. We show that for a wide range of (deprojected) Sersic profiles in a spherical potential, the tidal forces are compressive within a region which encloses most of the corresponding light of observed nuclear clusters in both late-type and early-type galaxies. In such models, tidal forces become disruptive nearly everywhere for relatively large Sersic indices n >= 3.5. We also show that the mass of a central massive object (CMO) required to remove all radial compressive tidal forces scales linearly with the mass of the host galaxy. If CMOs formed in (progenitor) galaxies with n ~ 1, we predict a mass fraction of ~ 0.1-0.5%, consistent with observations of nuclear clusters and super-massive black holes. While we find that tidal compression possibly drives the formation of CMOs in galaxies, beyond the central regions and on larger scales in clusters disruptive tidal forces might contribute to prevent gas from cooling.Comment: 19 pages, 4 figures. Accepted for publication in ApJ. High resolution version available at http://www-obs.univ-lyon1.fr/labo/perso/eric.emsellem/preprint

How Special are Brightest Cluster Galaxies? The Impact of Near-Infrared Luminosities on Scaling Relations for BCGs

Using the extended J, H and K magnitudes provided by the 2MASS data archive, we consider the position of brightest cluster galaxies (BCGs) in the observed relations between inferred supermassive black hole (SMBH) mass and the host galaxy properties, as well as their position in the stellar velocity dispersion and luminosity (sigma-L) relation, compared to E and S0 galaxies. We find that SMBH masses (M) derived from near-infrared (NIR) magnitudes do not exceed 10e9.5Msol and that these masses agree well with the predictions made from sigma. In the NIR, there is no evidence that BCGs leave the sigma-L relation defined by less luminous galaxies. The higher SMBH masses predicted from V-band luminosities (M~10e10.5Msol) are attributed to the presence of extended envelopes around the BCGs, however, this will need to be confirmed using deeper multiwavelength imaging.Comment: 4 pages, 7 figures (4 color), uses emulateapj.cls. Replaced with ApJ Letters Accepted version. Conclusions are unchange

Ubiquity of optical activity in planar metamaterial scatterers

Recently it was discovered that periodic lattices of metamaterial scatterers show optical activity, even if the scatterers or lattice show no 2D or 3D chirality, if the illumination breaks symmetry. In this Letter we demonstrate that such `pseudo-chirality' is intrinsic to any single planar metamaterial scatterer and in fact has a well-defined value at a universal bound. We argue that in any circuit model, a nonzero electric and magnetic polarizability derived from a single resonance automatically imply strong bianisotropy, i.e., magneto-electric cross polarizability at the universal bound set by energy conservation. We confirm our claim by extracting polarizability tensors and cross sections for handed excitation from transmission measurements on near-infrared split ring arrays, and electrodynamic simulations for diverse metamaterial scatterers.Comment: 5 pages, 4 figure

Probability distribution function of dipolar field in two-dimensional spin ensemble

We theoretically determine the probability distribution function of the net field of the random planar structure of dipoles which represent polarized particles. At small surface concentrations c of the point dipoles this distribution is expressed in terms of special functions. At the surface concentrations of the dipoles as high as 0.6 the dipolar field obey the Gaussian law. To obtain the distribution function within transitional region c<0.6, we propose the method based on the cumulant expansion. We calculate the parameters of the distributions for some specific configurations of the dipoles. The distribution functions of the ordered ensembles of the dipoles at the low and moderate surface concentrations have asymmetric shape with respect to distribution medians. The distribution functions allow to calculate various physical parameters of two-dimensional interacting nanoparticle ensembles.Comment: 9 pages, 3 figure

The origin of polar ring galaxies: evidence for galaxy formation by cold accretion

Polar ring galaxies are flattened stellar systems with an extended ring of gas and stars rotating in a plane almost perpendicular to the central galaxy. We show that their formation can occur naturally in a hierarchical universe where most low mass galaxies are assembled through the accretion of cold gas infalling along megaparsec scale filamentary structures. Within a large cosmological hydrodynamical simulation we find a system that closely resembles the classic polar ring galaxy NGC 4650A. How galaxies acquire their gas is a major uncertainty in models of galaxy formation and recent theoretical work has argued that cold accretion plays a major role. This idea is supported by our numerical simulations and the fact that polar ring galaxies are typically low mass systems.Comment: 4 pages, 5 figures, stability of the ring discussed, minor changes to match the accepted version by ApJL. A preprint with high-resolution figures is available at http://krone.physik.unizh.ch/~andrea/PolarRing/PolarRing.p

Fourier microscopy of single plasmonic scatterers

We report a new experimental technique for quantifying the angular distribution of light scattered by single plasmonic and metamaterial nanoscatterers, based on Fourier microscopy in a dark field confocal set up. This new set up is a necessary tool for quantifying the scattering properties of single plasmonic and meatamaterial building blocks, as well as small coupled clusters of such building blocks, which are expected to be the main ingredients of nano-antennas, light harvesting structures and transformation optics. We present a set of measurements on Au nanowires of different lengths and show how the radiation pattern of single Au nanowires evolve with wire length and as a function of driving polarization and wave vector.Comment: 15 pages, 6 color figure

Empirical Models for Dark Matter Halos. III. The Kormendy relation and the log(rho_e)-log(R_e) relation

We have recently shown that the 3-parameter density-profile model from Prugniel & Simien provides a better fit to simulated, galaxy- and cluster-sized, dark matter halos than an NFW-like model with arbitrary inner profile slope gamma (Paper I). By construction, the parameters of the Prugniel-Simien model equate to those of the Sersic R^{1/n} function fitted to the projected distribution. Using the Prugniel-Simien model, we are therefore able to show that the location of simulated (10^{12} M_sun) galaxy-sized dark matter halos in the _e-log(R_e) diagram coincides with that of brightest cluster galaxies, i.e., the dark matter halos appear consistent with the Kormendy relation defined by luminous elliptical galaxies. These objects are also seen to define the new, and equally strong, relation log(rho_e) = 0.5 - 2.5log(R_e), in which rho_e is the internal density at r=R_e. Simulated (10^{14.5} M_sun) cluster-sized dark matter halos and the gas component of real galaxy clusters follow the relation log(rho_e) = 2.5[1 - log(R_e)]. Given the shapes of the various density profiles, we are able to conclude that while dwarf elliptical galaxies and galaxy clusters can have dark matter halos with effective radii of comparable size to the effective radii of their baryonic component, luminous elliptical galaxies can not. For increasingly large elliptical galaxies, with increasingly large profile shapes `n', to be dark matter dominated at large radii requires dark matter halos with increasingly large effective radii compared to the effective radii of their stellar component.Comment: AJ, in press. (Paper I can be found at astro-ph/0509417