Near-infrared 0.15 arcsec resolution imaging of the Galactic center

Eckart, A.; Genzel, R.; Hofmann, R.; Sams, B.; Tacconi-Garman, L. E.

doi:10.1086/186810

Cited by 101 publications

(78 citation statements)

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“…The preferred value for the stellar mass within 1 pc is seen to be ∼1.5 × 10 6 M (isotropic) and ∼1.1 × 10 6 M (anisotropic). While early work (e.g., Sellgren et al 1990;Eckart et al 1993) found enclosed masses at R ≈ 0.5 pc that are comparable to what we have derived in this work, almost negligible amounts of extended, i.e. stellar, mass within R < 1 pc were reported in later work (see,e.g., Haller et al 1996;Genzel et al 2000;Schödel et al 2003).…”

Section: Mass Modeling: Cluster Masssupporting

confidence: 89%

“…They identified the NSC of the Milky Way (MW) and estimated its mass as 3.5 ± 1.5 × 10 7 M . The MW NSC is close to isothermal, with a power-law index around 1.8 (Becklin & Neugebauer 1968;Catchpole et al 1990;Haller et al 1996;Eckart et al 1993). Genzel et al (2003) showed that the MW NSC contains a central stellar cusp and no flat core.…”

Section: Introductionmentioning

confidence: 98%

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

Schödel¹,

Merritt²,

Eckart³

2009

A&A

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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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Section: Mass Modeling: Cluster Masssupporting

confidence: 89%

Section: Introductionmentioning

confidence: 98%

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

Schödel¹,

Merritt²,

Eckart³

2009

A&A

Self Cite

247

350

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“…Proper motions of the star cluster surrounding Sgr A * can be detected using near infrared speckle imaging techniques. Ongoing monitoring studies, conducted for the past ten years at the ESO NTT and Keck Telescope first, and at the ESO VLT more recently, have reached a staggering 0 ′′ .003 (0.1 mpc) astrometric accuracy in the stellar positions (Eckart et al 1993;Ghez et al 1998;Ghez et al 2000;Schödel et al 2003;Ghez et al 2003): proper motion has been measured for over 40 stars within 1 ′′ .2 of Sgr A * ; deviations from linear motion has been detected for eight stars and four stars in particular have passed the pericenter of their orbits since monitoring began (Ghez et al 2003;Schödel et al 2003). In the three cases for which accurate orbits can be traced, the stars orbit Sgr A * with periods between 15 and 71 years, reaching as close as 87 A.U.…”

Section: A Special Case: the Galactic Centermentioning

confidence: 99%

Supermassive Black Holes in Galactic Nuclei: Past, Present and Future Research

2005

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“…Two explanations are discussed for the presence of these stars, though neither is satisfactory: formation out of colliding or interacting giants (Eckart et al 1993;Genzel et al 2003;Ghez et al 2003Ghez et al , 2005 or scattering from the disk of young stars (Alexander & Livio 2004).…”

Section: Introductionmentioning

confidence: 99%

Composition of the galactic center star cluster

Buchholz

Schödel

Eckart

2009

A&A

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174

339

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Context. The GC is the closest galactic nucleus, offering the unique possibility of studying the population of a dense stellar cluster surrounding an SMBH. Aims. The goals of this work are to develop a new method of separating early and late type stellar components of a dense stellar cluster based on narrow band filters, applying it to the central parsec of the GC, and conducting a population analysis of this area. Methods. We use AO assisted observations obtained at the ESO VLT in the NIR H-band and 7 intermediate bands covering the NIR K-band. A comparison of the resulting SEDs with a blackbody of variable extinction then allows us to determine the presence and strength of a CO absorption feature to distinguish between early and late type stars.Results. This new method is suitable for classifying K giants (and later), as well as B2 main sequence (and earlier) stars that are brighter than 15.5 mag in the K band in the central parsec. Compared to previous spectroscopic investigations that are limited to 13-14 mag, this represents a major improvement in the depth of the observations and reduces the needed observation time. Extremely red objects and foreground sources can also be reliably removed from the sample. Comparison to sources of known classification indicates that the method has an accuracy of better than ∼87%. We classify 312 stars as early type candidates out of a sample of 5914 sources. Several results, such as the shape of the KLF and the spatial distribution of both early and late type stars, confirm and extend previous works. The distribution of the early type stars can be fitted with a steep power law (β 1 = −1.49 ± 0.12), alternatively with a broken power law, β 1−10 = −1.08 ± 0.12, β 10−20 = −3.46 ± 0.58, since we find a drop in the early type density at ∼10 . We also detect early type candidates outside of 0.5 pc in significant numbers for the first time. The late type density function shows an inversion in the inner 6 , with a power-law slope of β R<6 = 0.17 ± 0.09. The late type KLF has a power-law slope of 0.30 ± 0.01, closely resembling the KLF obtained for the bulge of the Milky Way. The early type KLF has a much flatter slope of (0.14 ± 0.02). Our results agree best with an in-situ star formation scenario.

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Near-infrared 0.15 arcsec resolution imaging of the Galactic center

Cited by 101 publications

References 0 publications

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

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

Supermassive Black Holes in Galactic Nuclei: Past, Present and Future Research

Composition of the galactic center star cluster

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