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Search Results: 1 - 10 of 167719 matches for " E. Pignatelli "
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A Massive Dark Object in the S0 galaxy NGC 4350
E. Pignatelli
Physics , 2000,
Abstract: We present a new detection of a Massive Dark Object in the S0 Galaxy NGC 4350, obtained applying a new dynamical model on ground-based photometric and kinematic data already present in literature.
Multi-component models for disk galaxies. A test case on NGC 5866
E. Pignatelli
Physics , 1999,
Abstract: We present an application of a new set of detailed, self-consistent, dynamical models for disc galaxies. We start from the hypothesis that each galaxy can be decomposed in a bulge, following the r^{1/4} law, and a disc with an exponential projected density profile; and that the isodensity surfaces of each component can be represented by similar concentric spheroids. After taking into account both the asymmetric drift effects and the integration along the line of sight, we produce the rotational velocity and velocity dispersion profile,_and_ the approximate shape of the line of sight velocity distributions for the stars as parameterized by the h3 and h4 coefficients of the Gauss-Hermite expansion of the line profile. Photometric and kinematical data have been taken from the literature for the test case of the S0 galaxy NGC 5866, for which detailed stellar kinematical data are available at different positions across the galaxy. Apart from the very inner, dust-obscured regions of the galaxy, where observational effects are likely to be dominant, the model successfully reproduce the whole set of dynamical data available as well as giving a good fit to the photometry. The galaxy is shown to have an isotropic velocity dispersion tensor, thus giving a hint on a dissipational formation process.
Multi-component models for disk galaxies. I. Stellar rotation and anisotropy
E. Pignatelli,G. Galletta
Physics , 1997,
Abstract: We present here a self-consistent, tridimensional model of a disc galaxy composed by a number of ellipsoidal distributions of matter having different flattening and density profile. The model is self-consistent and takes into account the observed luminosity distribution, the flattening profile and the stellar rotation- and velocity dispersion- curves. In this paper we considered the particular case of a disc galaxy composed by two spheroidal bodies: an exponential disc and a bulge following the r^{1/4} law. We studied the behavior of the stellar rotation- and velocity dispersion- profiles along the sequence of S0s and Spirals, identified by an increasing disc-to-bulge ratio. Inside every class, kinematic curves were produced by changing the relative concentration of the two components and the inclination of the galaxy with respect to the line of sight. The comparison with observational data requires only two scaling factors: the total mass of the galaxy, and the effective radius. The model allows also to detect the presence of anisotropy in the velocity distribution. In the special case of S0s, we explored the sensitivity of the kinematics of the model by changing the anisotropy and the flattening of the bulge. For intermediate flattening (0.4
Anatomy of giant spiral galaxies
E. Pignatelli,G. Galletta
Physics , 2000,
Abstract: We present B and I band photometry, gas and star kinematics and 3D modelling of 7 giant spiral galaxies. The stellar systems studied have morphological types spanning from S0/a to Sc and absolute magnitudes from -20.6 to -22.5. The spectra have been collected with the spectrographs Boller & Chivens and EFOSC2 of the 2.2m ESO-MPI telescope. Images have been taken with the same telescope. The models fit simultaneously the photometric and kinematics data using a disk+bulge tridimensional model. The distribution of luminous matter, coming from the fit of the photometric data is compared with the distribution of total matter derived from the velocity dispersion and velocity curves. The intrinsic properties of these galaxies, such as the disk/bulge mass ratio, the total mass and the scale length of the galaxy components are presented and discussed.
Morphological classification of high redshift galaxies
E. Pignatelli,G. Fasano
Physics , 2000,
Abstract: We present GASPHOT, a tool for automated surface photometry and morphological classification of galaxies in deep and wide fields. The requirements for any such tool are reviewed, and its use for the classification of high-z galaxies is presented. In the case if HDF-like images, for galaxies having a magnitude ranging from 24 to 27.5, the uncertainties on the photometric parameters derived from GASPHOT are respectively 0.02-0.1 on magnitude, 0.03 on the logarithm of the scale length, 0.02-0.5 on the Sersic index n used to classify the surface brightness profile of the galaxies. A comparison with the results achieved using Sextractor is presented.
Evidence for a Massive Dark Object in NGC 4350
E. Pignatelli,P. Salucci,L. Danese
Physics , 2000, DOI: 10.1046/j.1365-8711.2001.03942.x
Abstract: In this work we build a detailed dynamic model for a S0 galaxy possibly hosting a central massive dark object (MDO). We show that the photometric profiles and the kinematics along the major and minor axes, including the h3 and h4 profiles, imply the presence of a central MDO of mass M = 1.5 - 9.7 10^8 solar masses, i.e. 0.3-2.8% of the mass derived for the stellar spheroidal component. Models without MDO are unable to reproduce the kinematic properties of the inner stars and of the rapidly rotating nuclear gas. The stellar population comprise of an exponential disc (27% of the light) and a diffuse spheroidal component (73% of the light) that cannot be represented by a simple de Vaucouleurs profile at any radius. The M/L ratios we found for the stellar components (respectively 3.3 and 6.6) are typical of those of disc and elliptical galaxies.
Weighted hypersurfaces with either assigned volume or many vanishing plurigenera
E. Ballico,R. Pignatelli,L. Tasin
Mathematics , 2011,
Abstract: In this paper we construct, for every n, smooth varieties of general type of dimension n with the first $\lfloor \frac{n-2}{3} \rfloor$ plurigenera equal to zero. Hacon-McKernan, Takayama and Tsuji have recently shown that there are numbers $r_n$ such that, for all r > $r_n$, the r-canonical map of every variety of general type of dimension n is birational. Our examples show that $r_n$ grows at least quadratically as a function of n. Moreover they show that the minimal volume of a variety of general type of dimension n is smaller than $\frac{3^{n+1}}{(n-1)^{n}}$. In addition we prove that for every positive rational number q there are smooth varieties of general type with volume q and dimension arbitrarily big.
The moduli space of surfaces with $K^2=6, p_g=4$
Ingrid C. Bauer,Fabrizio M. E. Catanese,Roberto Pignatelli
Mathematics , 2004,
Abstract: In this paper we answer a question posed by Horikawa in 1978, who showed that the above moduli space is composed of 11 locally closed strata building up 4 irreducible components and having at most 3 connected components. We prove that the number of connected components is at most two and pose the question whether this number is exactly two. The main new idea is to analyse the strata in the moduli space where the canonical divisor is 2-divisible on the canonical model (as a Weil divisor). In this way we obtain a semicanonical ring $\B$ which is a Gorenstein ring of codimension 4 for type $III_b$ and of codimension 1 for type II. We use one of the formats introduced by Dicks and Reid for Gorenstein rings of codimension 4, the one of 4x4 Pfaffians of antisymmetric extrasymmetric 6x6 matrices.
Some (big) irreducible components of the moduli space of minimal surfaces of general type with $p_g=q=1$ and $K^2=4$
Roberto Pignatelli
Mathematics , 2008,
Abstract: In this paper we study the minimal surfaces of general type with $p_g=q=1$ and $K^2=4$ whose Albanese general fibre has genus 2, classifying those such that the direct image (under the Albanese morphism) of the bicanonical sheaf is sum of line bundles. We find 8 unirational families, all of dimension strictly bigger than the expected one. These families are pairwise disjoint irreducible components of the moduli space of minimal surfaces of general type.
On surfaces with a canonical pencil
Roberto Pignatelli
Mathematics , 2009,
Abstract: We classify the minimal surfaces of general type with $K^2 \leq 4\chi-8$ whose canonical map is composed with a pencil, up to a finite number of families. More precisely we prove that there is exactly one irreducible family for each value of $\chi \gg 0$, $4\chi-10 \leq K^2 \leq 4\chi-8$. All these surfaces are complete intersections in a toric $4-$fold and bidouble covers of Hirzebruch surfaces. The surfaces with $K^2=4\chi-8$ were previously constructed by Catanese as bidouble covers of $\PP^1 \times \PP^1$.
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