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Chatzopoulos S.,Max Planck Institute For Extraterrestrische Physic | Fritz T.K.,University of Virginia | Gerhard O.,Max Planck Institute For Extraterrestrische Physic | Gillessen S.,Max Planck Institute For Extraterrestrische Physic | And 4 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

We derive new constraints on the mass, rotation, orbit structure, and statistical parallax of the Galactic old nuclear star cluster and the mass of the supermassive black hole. We combine star counts and kinematic data from Fritz et al., including 2500 line-of-sight velocities and 10 000 proper motions obtained with VLT instruments. We show that the difference between the proper motion dispersions σl and σb cannot be explained by rotation, but is a consequence of the flattening of the nuclear cluster. We fit the surface density distribution of stars in the central 1000 arcsec by a superposition of a spheroidal cluster with scale ~100 arcsec and a much larger nuclear disc component. We compute the self-consistent two-integral distribution function f(E, Lz) for this density model, and add rotation selfconsistently. We find that (i) the orbit structure of the f(E, Lz) gives an excellent match to the observed velocity dispersion profiles as well as the proper motion and line-of-sight velocity histograms, including the double-peak in the vl-histograms. (ii) This requires an axial ratio near q1 = 0.7 consistent with our determination from star counts, q1 = 0.73 ± 0.04 for r < 70 arcsec. (iii) The nuclear star cluster is approximately described by an isotropic rotator model. (iv) Using the corresponding Jeans equations to fit the proper motion and line-of-sight velocity dispersions, we obtain best estimates for the nuclear star cluster mass, black hole mass, and distance M*(r < 100 arcsec) = (8.94 ± 0.31stat ± 0.9syst) × 106M, M• =(3.86±0.14stat ±0.4syst)×106M, and R0 =8.27±0.09stat ±0.1syst kpc, where the estimated systematic errors account for additional uncertainties in the dynamical modelling. (v) The combination of the cluster dynamics with the S-star orbits around Sgr A* strongly reduces the degeneracy between black hole mass and Galactic Centre distance present in previous S-star studies. A joint statistical analysis with the results of Gillessen et al., gives M• = (4.23 ± 0.14) × 106M and R0 = 8.33 ± 0.11 kpc. © 2014 The Authors. Source


Chatzopoulos S.,Max Planck Institute For Extraterrestrische Physic | Gerhard O.,Max Planck Institute For Extraterrestrische Physic | Fritz T.K.,University of Virginia | Wegg C.,Max Planck Institute For Extraterrestrische Physic | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2015

The mean absolute extinction towards the central parsec of the Milky Way is AK ≃ 3 mag, including both foreground and Galactic Centre dust. Here we present a measurement of dust extinction within the Galactic old nuclear star cluster (NSC), based on combining differential extinctions of NSC stars with their υl proper motions along Galactic longitude. Extinction within the NSC preferentially affects stars at its far side, and because the NSC rotates, this causes higher extinctions for NSC stars with negative υl, as well as an asymmetry in the υl-histograms. We model these effects using an axisymmetric dynamical model of the NSC in combination with simple models for the dust distribution. Comparing the predicted asymmetry to data for ~7100 stars in several NSC fields, we find that dust associated with the Galactic Centre mini-spiral with extinction AK ≃ 0.15-0.8 mag explains most of the data. The largest extinction AK ≃0.8mag is found in the region of theWestern arm of themini-spiral. Comparing with total AK determined from stellar colours, we determine the extinction in front of the NSC. Finally, we estimate that for a typical extinction of AK ≃ 0.4 the statistical parallax of the NSC changes by ~0.4 per cent. © 2015 The Authors. Source

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