The Influence of Interactions and Minor Mergers on the Structure of Galactic Disks: I.Observations and Disk Models

This paper is the first part in our series on the influence of tidal interactions and minor mergers on the radial and vertical disk structure of spiral galaxies. We report on the sample selection, our observations, and data reduction. Surface photometry of the optical and near infrared data of a sample of 110 highly-inclined/edge-on disk galaxies are presented. This sample consists of two subsamples of 61 non-interacting galaxies (control sample) and of 49 interacting galaxies/minor merging candidates. Additionally, 41 of these galaxies were observed in the near infrared. We show that the distribution of morphological types of both subsamples is almost indistinguishable, covering the range between 0 <= T <= 9. An improved, 3-dimensional disk modelling- and fitting procedure is described in order to analyze and to compare the disk structure of our sample galaxies by using characteristic parameters. We find that the vertical brightness profiles of galactic disks respond very sensitive even to small deviations from the perfect edge-on orientation. Hence, projection effects of slightly inclined disks may cause substantial changes in the value of the disk scale height and must therefore be considered in the subsequent study.Comment: LaTeX, 36 pages, 5 figures, complete series of papers incl. all figures of higher quality is available at http://aurora.as.arizona.edu/~schwarz

Properties of tidally-triggered vertical disk perturbations

We present a detailed analysis of the properties of warps and tidally-triggered perturbations perpendicular to the plane of 47 interacting/merging edge-on spiral galaxies. The derived parameters are compared with those obtained for a sample of 61 non-interacting edge-on spirals. The entire optical (R-band) sample used for this study was presented in two previous papers. We find that the scale height of disks in the interacting/merging sample is characterized by perturbations on both large (~disk cut-off radius) and short (~z0) scales, with amplitudes of the order of 280pc and 130pc on average, respectively. The size of these large (short) -scale instabilities corresponds to 14% (6%) of the mean disk scale height. This is a factor of 2 (1.5) larger than the value found for non-interacting galaxies. A hallmark of nearly all tidally distorted disks is a scale height that increases systematically with radial distance. The frequent occurrence and the significantly larger size of these gradients indicate that disk asymmetries on large scales are a common and persistent phenomenon, while local disturbances and bending instabilities decline on shorter timescales. Nearly all (93%) of the interacting/merging and 45% of the non-interacting galaxies studied are noticeably warped. Warps of interacting/merging galaxies are ~2.5 times larger on average than those observed in the non-interacting sample, with sizes of the order of 340pc and 140pc, respectively. This indicates that tidal distortions do considerably contribute to the formation and size of warps. However, they cannot entirely explain the frequent occurrence of warped disks.Comment: LaTeX, 35 pages, 6 figures, all figures and appendix of higher quality available at http://aurora.as.arizona.edu/~schwarz

Zero-Range Processes with Multiple Condensates: Statics and Dynamics

The steady-state distributions and dynamical behaviour of Zero Range Processes with hopping rates which are non-monotonic functions of the site occupation are studied. We consider two classes of non-monotonic hopping rates. The first results in a condensed phase containing a large (but subextensive) number of mesocondensates each containing a subextensive number of particles. The second results in a condensed phase containing a finite number of extensive condensates. We study the scaling behaviour of the peak in the distribution function corresponding to the condensates in both cases. In studying the dynamics of the condensate we identify two timescales: one for creation, the other for evaporation of condensates at a given site. The scaling behaviour of these timescales is studied within the Arrhenius law approach and by numerical simulations.Comment: 25 pages, 18 figure

Three-dimensional modelling of edge-on disk galaxies

We present detailed three-dimensional modelling of the stellar luminosity distribution for the disks of 31 relatively nearby (<= 110 Mpc) edge-on spiral galaxies. In contrast to most of the standard methods available in the literature we take into account the full three-dimensional information of the disk. We minimize the difference between the observed 2D-image and an image of our 3D-disk model integrated along the line of sight. Thereby we specify the inclination, the fitting function for the z-distribution of the disk, and the best values for the structural parameters such as scalelength, scaleheight, central surface brightness, and a disk cut-off radius. From a comparison of two independently developed methods we conclude, that the discrepancies e.g. for the scaleheights and scalelengths are of the order of ~10%. These differences are not due to the individual method itself, but rather to the selected fitting region, which masks the bulge component, the dust lane, or present foreground stars. Other serious limitations are small but appreciable intrinsic deviations of real disks compared to the simple input model. In this paper we describe the methods and present contour plots as well as radial profiles for all galaxies without previously published surface photometry. Resulting parameters are given for the complete sample.Comment: LaTeX, 25 pages, 28 figures higher quality figures available at http://www.astro.ruhr-uni-bochum.de/astro/publications/pub2000.htm

Non-gapped Fermi surfaces, quasiparticles and the anomalous temperature dependence of the near-EFE_F electronic states in the CMR oxide La2−2x_{2-2x}Sr1+2x_{1+2x}Mn2_2O7_7 with x=0.36x=0.36

After years of research into colossal magnetoresistant (CMR) manganites using bulk techniques, there has been a recent upsurge in experiments directly probing the electronic states at or near the surface of the bilayer CMR materials La$_{2-2x}$Sr$_{1+2x}$Mn$_2$O$_7$ using angle-resolved photoemission or scanning probe microscopy. Here we report new, temperature dependent, angle resolved photoemission data from single crystals with a doping level of $x=0.36$. The first important result is that there is no sign of a pseudogap in the charge channel of this material for temperatures below the Curie temperature $T_C$. The second important result concerns the temperature dependence of the electronic states. The temperature dependent changes in the Fermi surface spectra both at the zone face and zone diagonal regions in $k$-space indicate that the coherent quasiparticle weight disappears for temperatures significantly above $T_C$, and that the $k$-dependence of the T-induced changes in the spectra invalidate an interpretation of these data in terms of the superposition of a `universal' metallic spectrum and an insulating spectrum whose relative weight changes with temperature. In this sense, our data are not compatible with a phase separation scenario.Comment: 6 pages, 4 figure

Criticality and Condensation in a Non-Conserving Zero Range Process

The Zero-Range Process, in which particles hop between sites on a lattice under conserving dynamics, is a prototypical model for studying real-space condensation. Within this model the system is critical only at the transition point. Here we consider a non-conserving Zero-Range Process which is shown to exhibit generic critical phases which exist in a range of creation and annihilation parameters. The model also exhibits phases characterised by mesocondensates each of which contains a subextensive number of particles. A detailed phase diagram, delineating the various phases, is derived.Comment: 15 pages, 4 figure, published versi