Examinando por Autor "Puzia, Thomas H."

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    Ítem
    Globular cluster scale sizes in giant galaxies: orbital anisotropy and tidally underfilling clusters in M87, NGC 1399 and NGC 5128
    (OXFORD UNIV PRESS, 2016-08) Webb, Jeremy J.; Sills, Alison; Harris, William E.; Gómez, Matías; Paolillo, Maurizio; Woodley, Kristin A.; Puzia, Thomas H.
    We investigate the shallow increase in globular cluster half-light radii with projected galactocentric distance Rgc observed in the giant galaxies M87, NGC 1399, and NGC 5128. To model the trend in each galaxy, we explore the effects of orbital anisotropy and tidally underfilling clusters. While a strong degeneracy exists between the two parameters, we use kinematic studies to help constrain the distance Rβ beyond which cluster orbits become anisotropic, as well as the distance Rfα beyond which clusters are tidally underfilling. For M87 we find Rβ > 27 kpc and 20 < Rfα < 40 kpc and for NGC 1399 Rβ > 13 kpc and 10 < Rfα < 30 kpc. The connection of Rfα with each galaxy's mass profile indicates the relationship between size and Rgc may be imposed at formation, with only inner clusters being tidally affected. The best-fitting models suggest the dynamical histories of brightest cluster galaxies yield similar present-day distributions of cluster properties. For NGC 5128, the central giant in a small galaxy group, we find Rβ > 5 kpc and Rfα > 30 kpc. While we cannot rule out a dependence on Rgc, NGC 5128 is well fitted by a tidally filling cluster population with an isotropic distribution of orbits, suggesting it may have formed via an initial fast accretion phase. Perturbations from the surrounding environment may also affect a galaxy's orbital anisotropy profile, as outer clusters in M87 and NGC 1399 have primarily radial orbits while outer NGC 5128 clusters remain isotropic.
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    Ítem
    Observational evidence for a dark side to ngc 5128`s globular cluster system
    (Institute of Physics Publishing, 2015-05) Taylor, Matthew A.; Puzia, Thomas H.; Gomez, Matias; Woodley, Kristin A.
    We present a study of the dynamical properties of 125 compact stellar systems (CSSs) in the nearby giant elliptical galaxy NGC 5128, using high-resolution spectra (R ≈ 26, 000) obtained with Very Large Telescope/FLAMES. Our results provide evidence for a new type of star cluster, based on the CSS dynamical mass scaling relations. All radial velocity (vr) and line-of-sight velocity dispersion (σlos) measurements are performed with the penalized pixel fitting (ppxf ) technique, which provided σppxf estimates for 115 targets. The σppxf estimates are corrected to the 2D projected half-light radii, σ1/2, as well as the cluster cores, σ0, accounting for observational/aperture effects and are combined with structural parameters, from high spatial resolution imaging, in order to derive total dynamical masses (Mdyn) for 112 members of NGC 5128's star cluster system. In total, 89 CSSs have dynamical masses measured for the first time along with the corresponding dynamical mass-to-light ratios (ΥVdyn). We find two distinct sequences in the ΥVdyn-Mdyn plane, which are well approximated by power laws of the forms ΥVdyn ∝ Mdyn0.33±0.04 and ΥVdyn ∝ Mdyn0.79±0.04. The shallower sequence corresponds to the very bright tail of the globular cluster luminosity function (GCLF), while the steeper relation appears to be populated by a distinct group of objects that require significant dark gravitating components such as central massive black holes and/or exotically concentrated dark matter distributions. This result would suggest that the formation and evolution of these CSSs are markedly different from the "classical" globular clusters in NGC 5128 and the Local Group, despite the fact that these clusters have luminosities similar to the GCLF turnover magnitude. We include a thorough discussion of myriad factors potentially influencing our measurements. © 2015. The American Astronomical Society. All rights reserved.