Backlund transformations and Hamiltonian flows

In this work we show that, under certain conditions, parametric Backlund transformations (BTs) for a finite dimensional integrable system can be interpreted as solutions to the equations of motion defined by an associated non-autonomous Hamiltonian. The two systems share the same constants of motion. This observation lead to the identification of the Hamiltonian interpolating the iteration of the discrete map defined by the transformations, that indeed will be a linear combination of the integrals appearing in the spectral curve of the Lax matrix. An application to the Toda periodic lattice is given.Comment: 19 pages, 2 figures. to appear in J. Phys.

Polaronic signature in the metallic phase of La0.7Ca0.3MnO3 films detected by scanning tunneling spectroscopy

In this work we map tunnel conductance curves with nanometric spatial resolution, tracking polaronic quasiparticle excitations when cooling across the insulator-to-metal transition in La0.7Ca0.3MnO3 films. In the insulating phase the spectral signature of polarons, a depletion of conductance at low bias flanked by peaks, is detected all over the scanned surface. These features are still observed at the transition and persist on cooling into the metallic phase. Polaron-binding energy maps reveal that polarons are not confined to regions embedded in a highly-conducting matrix but are present over the whole field of view both above and below the transition temperature.Comment: 10 pages, 4 figure

The M(BH)-Sigma Relation for Supermassive Black Holes

We investigate the differences in the M(BH)-sigma relation derived recently by Ferrarese & Merritt (2000) and Gebhardt et al. (2000). The shallower slope found by the latter authors (3.75 vs. 4.8) is due partly to the use of a regression algorithm that ignores measurement errors, and partly to the value of the velocity dispersion adopted for a single galaxy, the Milky Way. A steeper relation is shown to provide a better fit to black hole masses derived from reverberation mapping studies. Combining the stellar dynamical, gas dynamical, and reverberation mapping mass estimates, we derive a best-fit relation M(BH) = 1.30 (+/- 0.36) X 10^8 (sigma_c/200)^{4.72(+/- 0.36)}, where M(BH) is in solar masses, and sigma in km/s.Comment: The Astrophysical Journal, in pres

The Dependence of Galaxy Shape on Luminosity and Surface Brightness Profile

For a sample of 96,951 galaxies from the Sloan Digital Sky Survey Data Release 3, we study the distribution of apparent axis ratios as a function of r-band absolute magnitude and surface brightness profile type. We use the parameter fracDeV to quantify the profile type (fracDeV = 1 for a de Vaucouleurs profile; fracDeV = 0 for an exponential profile). When the apparent axis ratio q_{am} is estimated from the moments of the light distribution, the roundest galaxies are very bright (M_r \sim -23) de Vaucouleurs galaxies and the flattest are modestly bright (M_r \sim -18) exponential galaxies. When the apparent axis ratio q_{25} is estimated from the axis ratio of the 25 mag/arcsec^2 isophote, we find that de Vaucouleurs galaxies are flatter than exponential galaxies of the same absolute magnitude. For a given surface brightness profile type, very bright galaxies are rounder, on average, than fainter galaxies. We deconvolve the distributions of apparent axis ratios to find the distribution of the intrinsic short-to-long axis ratio gamma, assuming constant triaxiality T. For all profile types and luminosities, the distribution of apparent axis ratios is inconsistent with a population of oblate spheroids, but is usually consistent with a population of prolate spheroids. Bright galaxies with a de Vaucouleurs profile (M_r < -21.84, fracDeV > 0.9) have a distribution of q_{am} that is consistent with triaxiality in the range 0.4 < T < 0.8, with mean intrinsic axis ratio 0.66 < gamma < 0.69. The fainter de Vaucouleurs galaxies are best fit with prolate spheroids (T = 1) with mean axis ratio gamma = 0.51.Comment: 32 pages, 12 figures, to appear in Ap

Gemini Deep Deep Survey VI: Massive Hdelta-strong galaxies at z=1

We show that there has been a dramatic decline in the abundance of massive galaxies with strong Hdelta stellar absorption lines from z=1.2 to the present. These ``Hdelta-strong'', or HDS, galaxies have undergone a recent and rapid break in their star-formation activity. Combining data from the Gemini Deep Deep and the Sloan Digital Sky Surveys to make mass-matched samples (M*>=10^10.2 Msun), with 25 and 50,255 galaxies, respectively), we find that the fraction of galaxies in an HDS phase has decreased from about 50% at z=1.2 to a few percent today. This decrease in fraction is due to an actual decrease in the number density of massive HDS systems by a factor of 2-4, coupled with an increase in the number density of massive galaxies by about 30 percent. We show that this result depends only weakly on the threshold chosen for the Hdelta equivalent width to define HDS systems (if greater than 4 A) and corresponds to a (1+z)^{2.5\pm 0.7} evolution. Spectral synthesis studies of the high-redshift population using the PEGASE code, treating Hdelta_A, EW[OII], Dn4000, and rest-frame colors, favor models in which the Balmer absorption features in massive Hdelta-strong systems are the echoes of intense episodes of star-formation that faded about 1 Gyr prior to the epoch of observation. The z=1.4-2 epoch appears to correspond to a time at which massive galaxies are in transition from a mode of sustained star formation to a relatively quiescent mode with weak and rare star-formation episodes. We argue that the most likely local descendants of the distant massive HDS galaxies are passively evolving massive galaxies in the field and small groups.Comment: 16 pages, 12 figures, 3 tables, uses emulateapj.sty; updated to match the version accepted by ApJ. One figure added, conclusions unchange

Directional vortex motion guided by artificially induced mesoscopic potentials

Rectangular pinning arrays of Ni dots define a potential landscape for vortex motion in Nb films. Magnetotransport experiments in which two in-plane orthogonal electrical currents are injected simultaneously allow selecting the direction and magnitude of the Lorentz force on the vortex-lattice, thus providing the angular dependence of the vortex motion. The background dissipation depends on angle at low magnetic fields, which is progressively smeared out with increasing field. The periodic potential locks in the vortex motion along channeling directions. Because of this, vortex-lattice direction of motion is up to 85o away from the applied Lorentz force direction.Comment: PDF file includes figure

The MACHO Project Hubble Space Telescope Follow-Up: Preliminary Results on the Location of the Large Magellanic Cloud Microlensing Source Stars

We attempt to determine whether the MACHO microlensing source stars are drawn from the average population of the LMC or from a population behind the LMC by examining the HST color-magnitude diagram (CMD) of microlensing source stars. We present WFPC2 HST photometry of eight MACHO microlensing source stars and the surrounding fields in the LMC. The microlensing source stars are identified by deriving accurate centroids in the ground-based MACHO images using difference image analysis (DIA) and then transforming the DIA coordinates to the HST frame. We consider in detail a model for the background population of source stars based on that presented by Zhao, Graff & Guhathakurta. In this model, the source stars have an additional reddening = 0.13 mag and a slightly larger distance modulus ~ 0.3 mag than the average LMC population. We also investigate a series of source star models, varying the relative fraction of source stars drawn from the average and background populations and the displacement of the background population from the LMC. Due to the small number of analyzed events the distribution of probabilities of different models is rather flat. A shallow maximum occurs at a fraction s_LMC ~ 0.8 of the source stars in the LMC. This is consistent with the interpretation that a significant fraction of observed microlensing events are due to lenses in the Milky Way halo, but does not definitively exclude other models.Comment: revised version, results slightly changed, accepted by Ap

Constraints on the distribution of absorption in the X-ray selected AGN population found in the 13H XMM-Newton/Chandra deep field

We present an analysis of the X-ray properties of sources detected in the 13H XMM-Newton deep (200ks) field. In order to constrain the absorbed AGN population, we use extensive Monte Carlo simulations to directly compare the X-ray colours of observed sources with those predicted by several model distributions. We have tested the simplest form of the AGN unified scheme, whereby the intrinsic XLF of absorbed AGN is set to be the same as that of their unabsorbed brethren, coupled with various model distributions of absorption. The best fitting of these models sets the fraction of AGN with absorbing column NH, proportional to (logNH)^8. We have also tested two extensions to the unified scheme: an evolving absorption scenario, and a luminosity dependent model distribution. Both of these provide poorer matches to the observed X-ray colour distributions than the best fitting simple unified model. We find that a luminosity dependent density evolution XLF reproduces poorly the 0.5-2 keV source counts seen in the 13H field. Field to field variations could be the cause of this disparity. Computing the simulated X-ray colours with a simple absorbed power-law + reflection spectral model is found to over-predict, by a factor of two, the fraction of hard sources that are completely absorbed below 0.5 keV, implying that an additional source of soft-band flux must be present for a number of the absorbed sources. Finally, we show that around 40% of the 13H sample are expected to be AGN with NH>10^22 cm^-2.Comment: 13 pages, 9 figures, Accepted for publication in MNRA

The VIRMOS deep imaging survey II: CFH12K BVRI optical data for the 0226-04 deep field

(abridged) In this paper we describe in detail the reduction, preparation and reliability of the photometric catalogues which comprise the 1.2 deg^2 CFH12K-VIRMOS deep field. The survey reaches a limiting magnitude of BAB~26.5, VAB~26.2, RAB~25.9 IAB~25.0 and contains 90,729 extended sources in the magnitude range 18.0<IAB<24.0. We demonstrate our catalogues are free from systematic biases and are complete and reliable down these limits. We estimate that the upper limit on bin-to-bin systematic photometric errors for the I- limited sample is ~10% in this magnitude range. We estimate that 68% of the catalogues sources have absolute per co-ordinate astrometric uncertainties less than ~0.38" and ~0.32" (alpha,delta). Our internal (filter-to-filter) per co-ordinate astrometric uncertainties are 0.08" and 0.08" (alpha,delta). We quantify the completeness of our survey in the joint space defined by object total magnitude and peak surface brightness. Finally, we present numerous comparisons between our catalogues and published literature data: galaxy and star counts, galaxy and stellar colours, and the clustering of both point-like and extended populations. In all cases our measurements are in excellent agreement with literature data to IAB<24.0. This combination of depth and areal coverage makes this multi-colour catalogue a solid foundation to select galaxies for follow-up spectroscopy with VIMOS on the ESO-VLT and a unique database to study the formation and evolution of the faint galaxy population to z~1 and beyond.Comment: 18 pages, 23 figures, accepted for publication in A&