Publications (7)0 Total impact
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Article: Global Gravitationally-Organized Spiral Waves and the Structure of NGC5247
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ABSTRACT: Using observational data, we build numerical N-body, hydrodynamical and combined equilibrium models for the spiral galaxy NGC 5247. The models turn out to be unstable as regards spiral structure formation. We simulate scenarios of spiral structure formation for different sets of equilibrium rotation curves, radial velocity-dispersion profiles and disc thicknesses and demonstrate that in all cases the simulated spiral pattern agrees qualitatively with the observed morphology of NGC 5247. We also demonstrate that an admixture of a gaseous component with a mass of about a few per cent of the total mass of the disc increases the lifetime of a spiral pattern by approximately 30 per cent. The simulated spiral pattern in this case lasts for about 3 Gyr from the beginning of the growth of perturbations.12/2012; 427:1983-1993. -
Article: Global gravitationally organized spiral waves and the structure of NGC 5247
mnras. 12/2012; 427:1983-1993. -
Article: The 3D Velocity Structure of the Thick Disk from SPM4 and RAVE DR2
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ABSTRACT: We analyze the 3D kinematics of a sample of $\sim 4400$ red clump stars ranging between 5 and 10 kpc from the Galactic center and up to 3 kpc from the Galactic plane. This sample is representative for the metal-rich ([Fe/H] = -0.6 to 0.5) thick disk. Absolute proper motions are from the fourth release of the Southern Proper Motion Program, and radial velocities from the second release of the Radial Velocity Experiment. The derived kinematical properties of the thick disk include: the rotational velocity gradient $\partial V_{\theta} / \partial z = -25.2 \pm 2.1$ km s$^{-1}$ kpc$^{-1}$, velocity dispersions $(\sigma_{V_R}, \sigma_{V_{\theta}}, \sigma_{V_z})|_{z=1} = (70.4, 48.0, 36.2) \pm(4.1,8.3,4.0)$ km s$^{-1}$, and velocity-ellipsoid tilt angle $\alpha_{Rz} = 8.6\arcdeg \pm 1.8 \arcdeg$. Our dynamical estimate of the thin-disk scale length is $R_{thin} = 2.0 \pm 0.4$ kpc and the thick-disk scale height is $z_{thick} = 0.7 \pm 0.1$ kpc. The observed orbital eccentricity distribution compared with those from four different models of the formation of the thick disk from Sales et al. favor the gas-rich merger model and the minor merger heating model. Interestingly, when referred to the currently accepted value of the LSR, stars more distant than 0.7 kpc from the Sun show a net average radial velocity of $13 \pm3 $ km s$^{-1}$. This result is seen in previous kinematical studiesusing other tracers at distances larger than $\sim 1$ kpc. We suggest this motion reflects an inward perturbation of the locally-defined LSR induced by the spiral density wave. Comment: accepted for publication in ApJ11/2010; -
Article: The vertical velocity dispersion profile of the Galactic thick disk
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ABSTRACT: We present the results of radial velocity measurements of 770 thick disk red giants toward the South Galactic Pole, vertically distributed from 0.5 kpc to 5 kpc with respect to the Galactic plane. We find a small gradient in the vertical velocity dispersion (sigma_W) of 3.8+/-0.8 km/s kpc. Even more noteworthy, our values of $\sigma_W$ are small compared to literature values: in the middle of the vertical height range we find sigma_W(z=2kpc)=30 km/s. We found no possible explanation for this small value of sigma_W in terms of sample contamination by thin disk stars, nor by wrong assumptions regarding the metallicity distribution and the derived distances.01/2008; -
Article: Velocity Shear of the Thick Disk from SPM3 Proper Motions at the South Galactic Pole
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ABSTRACT: The kinematical properties of the Galactic Thick Disk are studied using absolute proper motions from the SPM3 Catalog and 2MASS near-infrared photometry for a sample of ~1200 red giants in the direction of the South Galactic Pole. The photometrically-selected sample is dominated by Thick Disk stars, as indicated by the number-density distribution that varies with distance from the Galactic plane as a single-valued exponential over the range 1<z<4 kpc. The inferred scale height of the Thick Disk is 0.783 +/- 0.048 kpc. The kinematics of the sample are also consistent with disk-like motion. The U-velocity component is roughly constant, reflecting the Sun's peculiar motion, while a considerable shear is seen in the mean rotational velocity, V. The V-velocity profile's dependence on z is linear, with a gradient of dV/dz = -30 +/- 3 km/s/kpc. The velocity dispersions, in both U and V, show a lesser gradient of about 9 +/- 3 km/s/kpc. We demonstrate that the derived velocity and velocity-dispersion profiles are consistent with the assumptions of dynamical equilibrium and reasonable models of the overall Galactic potential.08/2006; -
Article: Disruption of a Dwarf Galaxy Under Strong Shocking: The Origin of omega Centauri
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ABSTRACT: We perform N-body simulations of the dynamical evolution of a dwarf galaxy falling into the Milky Way galaxy in order to understand the formation scenario of the peculiar globular cluster $\omega$ Centauri. We use self-consistent models of the bulge and the disc of the Milky Way, as well as of the dwarf galaxy, and explore a range of dwarf models with different density distributions. Namely, we use King (1966) and Hernquist (1990) density profiles to model the density distribution in the dwarf. The central region of our King model has a density profile approximately $\propto r^{-2}$, while that of the Hernquist model is $\propto r^{-1}$. The difference in the dwarf's density distributions leads to distinct evolutionary scenarios. The King model dwarf loses its mass exponentially as a function of apocentric distance, with the mass-loss rate depending on the initial mass and size of the dwarf. Regardless of the initial mass and size, the King model dwarf remains more massive than $10^8$ \msun after a few Gyr of evolution. The Hernquist model dwarf experiences an accelerated mass loss, and the mass of the remnant falls below $10^8$ \msun within a few Gyr. By exploring an appropriate set of parameters, we find a Hernquist model that can attain the mass and orbital characteristics of $\omega$ Cen after a few Gyr. Comment: 12 pages, 14 figures, MNRAS in press02/2004; -
Article: Local Surface Density of the Galactic Disk from a 3-D Stellar Velocity Sample
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ABSTRACT: We have re-estimated the surface density of the Galactic disk in the solar neighborhood within $\pm$ 0.4 kpc of the Sun using parallaxes and proper motions of a kinematically and spatially unbiased sample of 1476 old bright red giant stars from the Hipparcos catalog with measured radial velocities from Barbier-Brossat & Figon (2000). We determine the vertical distribution of the red giants as well as the vertical velocity dispersion of the sample, (14.4 $\pm$ 0.26 km/sec), and combine these to derive the surface density of gravitating matter in the Galactic disk as a function of the galactic coordinate $z$. The surface density of the disk increases from 10.5 $\pm$ 0.5 $M_{\odot}$ / pc$^2$ within $\pm$ 50 pc to 42 $\pm$ 6 $M_{\odot}$ / pc$^2$ within $\pm$ 350 pc. The estimated volume density of the galactic disk within $\pm$ 50 pc is about 0.1 $M_{\odot}$ / pc$^3$ which is close to the volume density estimates of the observed baryonic matter in the solar neighborhood. Comment: 24 pages, 15 figures, AJ in press08/2003;
