Globular cluster system and Milky Way properties revisited

被引：0

作者：

Bica, E. ^{[1
]}

Bonatto, C. ^{[1
]}

Barbuy, B. ^{[2
]}

Ortolani, S. ^{[3
]}

机构：

[1] Universidade Federal do Rio Grande do Sul, Instituto de Física, CP 15051, Porto Alegre 91501-970, RS, Brazil

[2] Universidade de São Paulo, Dept. de Astronomia, Rua do Matão 1226, São Paulo 05508-090, Brazil

[3] Università di Padova, Dipartimento di Astronomia, Vicolo dell'Osservatorio 2, 35122 Padova, Italy

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Astronomy and Astrophysics | 1600年 / 450卷 / 01期

关键词：

Aims. Updated data of the 153 Galactic globular clusters are used to readdress fundamental parameters of the Milky Way; such as the distance of the Sun to the Galactic centre; the bulge and halo structural parameters; and cluster destruction rates. Methods. We build a reduced sample that has been decontaminated of all the clusters younger than 10 Gyr and of those with retrograde orbits and/or evidence of relation to dwarf galaxies. The reduced sample contains 116 globular clusters that are tested for whether they were formed in the primordial collapse. Results. The 33 metal-rich globular clusters ([Fe/H] ≥ -0.75) of the reduced sample basically extend to the Solar circle and are distributed over a region with the projected axial-ratios typical of an oblate spheroidal; Δx : Δy : Δz 1.0 : 0.9 : 0.4. Those outside this region appear to be related to accretion. The 81 metal-poor globular clusters span a nearly spherical region of axial-ratios 1.0 : 1.0 : 0.8 extending from the central parts to the outer halo; although several clusters in the external region still require detailed studies to unravel their origin as accretion or collapse. A new estimate of the Sun's distance to the Galactic centre; based on the symmetries of the spatial distribution of 116 globular clusters; is provided with a considerably smaller uncertainty than in previous determinations using globular clusters; Ro = 7.2 ± 0.3 kpc. The metal-rich and metal-poor radial-density distributions flatten for RGC &le 2 kpc and are represented well over the full Galactocentric distance range both by a power-law with a core-like term and Sérsic's law; at large distances they fall off as ∼R-39. Conclusions. Both metallicity components appear to have a common origin that is different from that of the dark matter halo. Structural similarities between the metal-rich and metal-poor radial distributions and the stellar halo are consistent with a scenario where part of the reduced sample was formed in the primordial collapse and part was accreted in an early period of merging. This applies to the bulge as well; suggesting an early merger affecting the central parts of the Galaxy. The present decontamination procedure is not sensitive to all accretions (especially prograde) during the first Gyr; since the observed radial density profiles still preserve traces of the earliest merger(s). We estimate that the present globular cluster population corresponds to &le23 ± 6% of the original one. The fact that the volume-density radial distributions of the metal-rich and metal-poor globular clusters of the reduced sample follow both a core-like power-law; and Sérsic's law indicates that we are dealing with spheroidal subsystems at all scales. © ESO 2006;

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页码：105 / 115

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