Stellar Populations in the Nuclei of Late‐Type Spiral Galaxies

Walcher, C. J.; Böker, Torsten; Charlot, S.; Ho, Luis C.; Rix, Hans─Walter; Rossa, J.; Shields, J. C.; Marel, Roeland P. van der

doi:10.1086/505166

Cited by 211 publications

(311 citation statements)

References 78 publications

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“…A comparable result has also been deduced for 9 NCs of very late type bulgeless spirals by Walcher et al (2006) by means of a high-resolution spectroscopic survey with the VLT Ultraviolet and Visual Echelle Spectrograph (UVES). Genzel et al (2003), in their study of the stellar cuspy distribution around the supermassive black hole (SBH) in the Galactic center, found that the K-band luminosity function of the local NC (within 9 00 of Sgr A Ã ) resembles that of the large-scale Galactic bulge, but shows an excess of stars at K s 14.…”

Section: Introductionsupporting

confidence: 75%

Merging of Globular Clusters in Inner Galactic Regions. II. Nuclear Star Cluster Formation

Capuzzo–Dolcetta

Miocchi

2008

ApJ

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In this series of papers, we present the results of detailed N-body simulations of the interaction of a sample of four massive globular clusters in the inner region of a triaxial galaxy for two different sets of initial conditions that correspond to different initial density concentrations. A full merging of the clusters takes place, leading to a slowly evolving cluster that is quite similar to observed nuclear clusters. Actually, both the density and the velocity dispersion profiles match qualitatively, and also quantitatively after scaling to a larger number of merger globulars, with the observed features of many nucleated galaxies. In the case of dense initial clusters, the merger remnant shows a density profile more concentrated than that of the progenitors, with a central density higher than the sum of the progenitors' central densities and an effective radius compatible with observed nuclear values. These findings support the idea that a massive nuclear cluster may have formed in the early phases of the mother galaxy's evolution and led to the formation of a nucleus, which in many galaxies has a luminosity profile similar to that of an extended King model. A correlation with galactic nuclear activity is suggested.

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Section: Introductionsupporting

confidence: 75%

Merging of Globular Clusters in Inner Galactic Regions. II. Nuclear Star Cluster Formation

Capuzzo–Dolcetta

Miocchi

2008

ApJ

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“…Studies have shown that star formation in nuclear star clusters continues until the present day (Walcher et al 2006). Observations of nuclear clusters in edge-on spirals reveal that young stars are located in flattened disks (Seth et al 2006(Seth et al , 2008b.…”

Section: Introductionmentioning

confidence: 99%

KMOS view of the Galactic centre

Feldmeier-Krause

Neumayer

Schödel

et al. 2015

A&A

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106

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Context. The Galactic centre hosts a crowded, dense nuclear star cluster with a half-light radius of 4 pc. Most of the stars in the Galactic centre are cool late-type stars, but there are also > ∼ 100 hot early-type stars in the central parsec of the Milky Way. These stars are only 3−8 Myr old. Aims. Our knowledge of the number and distribution of early-type stars in the Galactic centre is incomplete. Only a few spectroscopic observations have been made beyond a projected distance of 0.5 pc of the Galactic centre. The distribution and kinematics of earlytype stars are essential to understand the formation and growth of the nuclear star cluster. Methods. We cover the central >4 pc 2 (0.75 sq. arcmin) of the Galactic centre using the integral-field spectrograph KMOS (VLT). We extracted more than 1000 spectra from individual stars and identified early-type stars based on their spectra. Results. Our data set contains 114 bright early-type stars: 6 have narrow emission lines, 23 are Wolf-Rayet stars, 9 stars have featureless spectra, and 76 are O/B type stars. Our wide-field spectroscopic data confirm that the distribution of young stars is compact, with 90% of the young stars identified within 0.5 pc of the nucleus. We identify 24 new O/B stars primarily at large radii. We estimate photometric masses of the O/B stars and show that the total mass in the young population is > ∼ 12 000 M . The O/B stars all appear to be bound to the Milky Way nuclear star cluster, while less than 30% belong to the clockwise rotating disk. We add one new star to the sample of stars affiliated with this disk. Conclusions. The central concentration of the early-type stars is a strong argument that they have formed in situ. An alternative scenario, in which the stars formed outside the Galactic centre in a cluster that migrated to the centre, is refuted. A large part of the young O/B stars is not on the disk, which either means that the early-type stars did not all form on the same disk or that the disk is dissolving rapidly.

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“…NSCs are the densest known star clusters in the Universe. Most NSCs contain a mixed stellar population with signs of repeated episodes of star formation (Walcher et al 2006). Recent research suggests that there exists a Appendices are only available in electronic form at http://www.aanda.org…”

Section: Introductionmentioning

confidence: 99%

The nuclear star cluster of the Milky Way: proper motions and mass

Schödel¹,

Merritt²,

Eckart³

2009

A&A

247

350

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Context. Nuclear star clusters (NSCs) are located at the photometric and dynamical centers of the majority of galaxies. They are among the densest star clusters in the Universe. The NSC in the Milky Way is the only object of this class that can be resolved into individual stars. The massive black hole Sagittarius A* is located at the dynamical center of the Milky Way NSC. Aims. In this work we examine the proper motions of stars out to distances of 1.0 pc from Sgr A*. The aim is to examine the velocity structure of the MW NSC and acquire a reliable estimate of the stellar mass in the central parsec of the MW NSC, in addition to the well-known black hole mass. Methods. We use multi-epoch adaptive optics assisted near-infrared observations of the central parsec of the Galaxy obtained with NACO/CONICA at the ESO VLT. Stellar positions are measured via PSF fitting in the individual images and transformed into a common reference frame via suitable sets of reference stars. Results. We measured the proper motions of more than 6000 stars within ∼1.0 pc of Sagittarius A*. The full data set is provided in this work. We largely exclude the known early-type stars with their peculiar dynamical properties from the dynamical analysis. The cluster is found to rotate parallel to Galactic rotation, while the velocity dispersion appears isotropic (or anisotropy may be masked by the cluster rotation). The Keplerian fall-off of the velocity dispersion due to the point mass of Sgr A* is clearly detectable only at R < ∼ 0.3 pc. Nonparametric isotropic and anisotropic Jeans models are applied to the data. They imply a best-fit black hole mass of 3.6 +0.2 −0.4 × 10 6 M . Although this value is slightly lower than the current canonical value of 4.0 × 10 6 M , this is the first time that a proper motion analysis provides a mass for Sagittarius A* that is consistent with the mass inferred from orbits of individual stars. The point mass of Sagittarius A* is not sufficient to explain the velocity data. In addition to the black hole, the models require the presence of an extended mass of 0.5−1.5 × 10 6 M in the central parsec. This is the first time that the extended mass of the nuclear star cluster is unambiguously detected. The influence of the extended mass on the gravitational potential becomes notable at distances > ∼ 0.4 pc from Sgr A*. Constraints on the distribution of this extended mass are weak. The extended mass can be explained well by the mass of the stars that make up the cluster.

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Stellar Populations in the Nuclei of Late‐Type Spiral Galaxies

Cited by 211 publications

References 78 publications

Merging of Globular Clusters in Inner Galactic Regions. II. Nuclear Star Cluster Formation

Merging of Globular Clusters in Inner Galactic Regions. II. Nuclear Star Cluster Formation

KMOS view of the Galactic centre

The nuclear star cluster of the Milky Way: proper motions and mass

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