Spheroidal

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Sidney Van Den Bergh - One of the best experts on this subject based on the ideXlab platform.

  • young globular clusters and dwarf Spheroidals
    The Astrophysical Journal, 2000
    Co-Authors: Sidney Van Den Bergh
    Abstract:

    Most of the globular clusters in the main body of the Galactic halo were formed almost simultaneously. However, globular cluster formation in dwarf Spheroidal galaxies appears to have extended over a significant fraction of a Hubble time. This suggests that the factors which suppressed late-time formation of globulars in the main body of the Galactic halo were not operative in dwarf Spheroidal galaxies. Possibly the presence of significant numbers of "young" globulars at RGC > 15 kps can be accounted for by the assumption that many of these objects were formed in Sagittarius-like (but not Fornax-like) dwarf Spheroidal galaxies, that were subsequently destroyed by Galactic tidal forces. It would be of interest to search for low-luminosity remnants of parental dwarf Spheroidals around the "young" globulars Eridanus, Palomar 1, 3, and 14. Furthermore, multicolor photometry could be used to search for the remnants of the superassociations, within which outer halo globular clusters originally formed. Such envelopes are expected to have been tidally stripped from globulars in the inner halo.

  • young globular clusters and dwarf Spheroidals
    arXiv: Astrophysics, 1999
    Co-Authors: Sidney Van Den Bergh
    Abstract:

    Most of the globular clusters in the main body of the Galactic halo were formed almost simultaneously. However, globular cluster formation in dwarf Spheroidal galaxies appears to have extended over a significant fraction of a Hubble time. This suggests that the factors which suppressed late-time formation of globulars in the main body of the Galactic halo were not operative in dwarf Spheroidal galaxies. Possibly the presence of significant numbers of ``young'' globulars at R_{GC} > 15 kpc can be accounted for by the assumption that many of these objects were formed in Sagittarius-like (but not Fornax-like) dwarf Spheroidal galaxies, that were subsequently destroyed by Galactic tidal forces. It would be of interest to search for low-luminosity remnants of parental dwarf Spheroidals around the ``young'' globulars Eridanus, Palomar 1, 3, 14, and Terzan 7. Furthermore multi-color photometry could be used to search for the remnants of the super-associations, within which outer halo globular clusters originally formed. Such envelopes are expected to have been tidally stripped from globulars in the inner halo.

Zhensen Wu - One of the best experts on this subject based on the ideXlab platform.

  • Scattering of a Spheroidal particle illuminated by a Gaussian beam
    Applied Optics, 2001
    Co-Authors: Zhensen Wu
    Abstract:

    An approach to expanding a Gaussian beam in terms of the Spheroidal wave functions in Spheroidal coordinates is presented. The beam-shape coefficients of the Gaussian beam in Spheroidal coordinates can be computed conveniently by use of the known expression for beam-shape coefficients, gn, in spherical coordinates. The unknown expansion coefficients of scattered and internal electromagnetic fields are determined by a system of equations derived from the boundary conditions for continuity of the tangential components of the electric and magnetic vectors across the surface of the spheroid. A solution to the problem of scattering of a Gaussian beam by a homogeneous prolate (or oblate) Spheroidal particle is obtained. The numerical values of the expansion coefficients and the scattered intensity distribution for incidence of an on-axis Gaussian beam are given.

  • The expansion coefficients of a Spheroidal particle illuminated by Gaussian beam
    IEEE Transactions on Antennas and Propagation, 2001
    Co-Authors: Zhensen Wu
    Abstract:

    We study the expansion of the Gaussian beam in terms of the prolate Spheroidal vector wavefunction. The expansion coefficients are determined. The numerical values of the Spheroidal eigenvalues and expansion coefficients have been computed.

Joe Wolf - One of the best experts on this subject based on the ideXlab platform.

  • local group dwarf Spheroidals correlated deviations from the baryonic tully fisher relation
    The Astrophysical Journal, 2010
    Co-Authors: Stacy S Mcgaugh, Joe Wolf
    Abstract:

    Local Group dwarf Spheroidal satellite galaxies are the faintest extragalactic stellar systems known. We examine recent data for these objects in the plane of the Baryonic Tully-Fisher Relation (BTFR). While some dwarf Spheroidals adhere to the BTFR, others deviate substantially. We examine the residuals from the BTFR and find that they are not random. The residuals correlate with luminosity, size, metallicity, ellipticity, and susceptibility of the dwarfs to tidal disruption in the sense that fainter, more elliptical, and tidally more susceptible dwarfs deviate farther from the BTFR. These correlations disfavor stochastic processes and suggest a role for tidal effects. We identify a test to distinguish between ?CDM and MOND based on the orbits of the dwarf satellites of the Milky Way and how stars are lost from them.

  • local group dwarf Spheroidals correlated deviations from the baryonic tully fisher relation
    arXiv: Cosmology and Nongalactic Astrophysics, 2010
    Co-Authors: Stacy S Mcgaugh, Joe Wolf
    Abstract:

    Local Group dwarf Spheroidal satellite galaxies are the faintest extragalactic stellar systems known. We examine recent data for these objects in the plane of the Baryonic Tully-Fisher Relation (BTFR). While some dwarf Spheroidals adhere to the BTFR, others deviate substantially. We examine the residuals from the BTFR and find that they are not random. The residuals correlate with luminosity, size, metallicity, ellipticity, and susceptibility of the dwarfs to tidal disruption in the sense that fainter, more elliptical, and tidally more susceptible dwarfs deviate farther from the BTFR. These correlations disfavor stochastic processes and suggest a role for tidal effects. We identify a test to distinguish between the {\Lambda}CDM and MOND based on the orbits of the dwarf satellites of the Milky Way and how stars are lost from them.

Lucio Mayer - One of the best experts on this subject based on the ideXlab platform.

  • early gas stripping as the origin of the darkest galaxies in the universe
    Nature, 2007
    Co-Authors: Lucio Mayer, Stelios Kazantzidis, Chiara Mastropietro, James Wadsley
    Abstract:

    The known galaxies most dominated by dark matter (Draco, Ursa Minor and Andromeda IX) are satellites of the Milky Way and the Andromeda galaxies. They are members of a class of faint galaxies, devoid of gas, known as dwarf Spheroidals, and have by far the highest ratio of dark to luminous matter. None of the models proposed to unravel their origin can simultaneously explain their exceptional dark matter content and their proximity to a much larger galaxy. Here we report simulations showing that the progenitors of these galaxies were probably gas-dominated dwarf galaxies that became satellites of a larger galaxy earlier than the other dwarf Spheroidals. We find that a combination of tidal shocks and ram pressure swept away the entire gas content of such progenitors about ten billion years ago because heating by the cosmic ultraviolet background kept the gas loosely bound: a tiny stellar component embedded in a relatively massive dark halo survived until today. All luminous galaxies should be surrounded by a few extremely dark-matter-dominated dwarf Spheroidal satellites, and these should have the shortest orbital periods among dwarf Spheroidals because they were accreted early.

  • tidal debris of dwarf Spheroidals as a probe of structure formation models
    Monthly Notices of the Royal Astronomical Society, 2002
    Co-Authors: Lucio Mayer, Ben Moore, Thomas R Quinn, Fabio Governato, Joachim Stadel
    Abstract:

    Recent observations suggest that Carina and other nearby dwarf Spheroidal galaxies (dSphs) are surrounded by unbound stars tidally stripped by the Milky Way. We have run high-resolution N-body simulations of dwarf galaxies orbiting within the Milky Way halo to determine if such observations can be explained with dark matter potentials like those implied by current structure formation models. We show that tidal forces acting on dwarfs with constant density cores or with cuspy profiles having a low concentration parameter (c 7) lead to flat outer stellar density profiles like that of Carina for a variety of orbital configurations. On the contrary, it is more difficult to remove stars from cuspy dark matter haloes with concentrations as high as predicted by cold dark matter (CDM) models at the mass scale of dwarf galaxies (c > 10), and the data can only be reproduced assuming nearly radial orbits. Our simulations show that Carina is losing mass at a fractional rate <0.1 Gyr −1 and its mass-to-light ratio could be inflated by at most a factor of 2 due to unbound stars projected along the line of sight. We follow the evolution of the tidal debris within a triaxial clumpy cold dark matter Milky Way halo which causes differential precession and small-scale heating of the stellar streams. This renders them useless as a dynamical tracer of the Galactic potential in CDM cosmogonies. Models with warm dark matter (WDM) or collisional fluid dark matter (FDM) produce dwarf haloes with lower central densities than CDM and would be consistent with the observed tidal tails even for orbits with eccentricities as low as indicated by current data on nearby dwarf Spheroidals. Galactic haloes in models with FDM are expected to be smooth and spherical and would be favoured by the detection of cold coherent streams such as that associated with the Sagittarius dwarf Spheroidal. In this respect the distribution of stellar streams on the plane of the sky can provide a novel test of the nature of the dark matter. On the other end, the streams could be similarly dispersed in lumpy CDM haloes and in smoother, triaxial WDM haloes.

Stacy S Mcgaugh - One of the best experts on this subject based on the ideXlab platform.

  • local group dwarf Spheroidals correlated deviations from the baryonic tully fisher relation
    The Astrophysical Journal, 2010
    Co-Authors: Stacy S Mcgaugh, Joe Wolf
    Abstract:

    Local Group dwarf Spheroidal satellite galaxies are the faintest extragalactic stellar systems known. We examine recent data for these objects in the plane of the Baryonic Tully-Fisher Relation (BTFR). While some dwarf Spheroidals adhere to the BTFR, others deviate substantially. We examine the residuals from the BTFR and find that they are not random. The residuals correlate with luminosity, size, metallicity, ellipticity, and susceptibility of the dwarfs to tidal disruption in the sense that fainter, more elliptical, and tidally more susceptible dwarfs deviate farther from the BTFR. These correlations disfavor stochastic processes and suggest a role for tidal effects. We identify a test to distinguish between ?CDM and MOND based on the orbits of the dwarf satellites of the Milky Way and how stars are lost from them.

  • local group dwarf Spheroidals correlated deviations from the baryonic tully fisher relation
    arXiv: Cosmology and Nongalactic Astrophysics, 2010
    Co-Authors: Stacy S Mcgaugh, Joe Wolf
    Abstract:

    Local Group dwarf Spheroidal satellite galaxies are the faintest extragalactic stellar systems known. We examine recent data for these objects in the plane of the Baryonic Tully-Fisher Relation (BTFR). While some dwarf Spheroidals adhere to the BTFR, others deviate substantially. We examine the residuals from the BTFR and find that they are not random. The residuals correlate with luminosity, size, metallicity, ellipticity, and susceptibility of the dwarfs to tidal disruption in the sense that fainter, more elliptical, and tidally more susceptible dwarfs deviate farther from the BTFR. These correlations disfavor stochastic processes and suggest a role for tidal effects. We identify a test to distinguish between the {\Lambda}CDM and MOND based on the orbits of the dwarf satellites of the Milky Way and how stars are lost from them.