The dynamical distance and intrinsic structure of the globular cluster ω Centauri

By Glenn van de Ven, R. V. D. Bosch, E. Verolme, P. de Zeeuw. 2005

235 citations recorded by the source corpus.

We determine the dynamical distance D, inclination i, mass-to-light ratio M/L and the intrinsic orbital structure of the globular cluster ω Cen, by fitting axisymmetric dynamical models to the ground-based proper motions of van Leeuwen et al. and line-of-sight velocities from four independent data-sets. We bring the kinematic measurements onto a common coordinate system, and select on cluster membership and on measurement error. This provides a homogeneous data-set of 2295 stars with proper motions accurate to 0.20 mas yr -1 and 2163 stars with line-of-sight velocities accurate to 2 km s -1 , covering a radial range out to about half the tidal radius. We correct the observed velocities for perspective rotation caused by the space motion of the cluster, and show that the residual solid-body rotation component in the proper motions (caused by relative rotation of the photographic plates from which they were derived) can be taken out without any modelling other than assuming axisymmetry. This also provides a tight constraint on I) tan i. The corrected mean velocity fields are consistent with regular rotation, and the velocity dispersion fields display significant deviations from isotropy. We model ω Cen with an axisymmetric implementation of Schwarzschild's orbit superposition method, which accurately fits the surface brightness distribution, makes no assumptions about the degree of velocity anisotropy in the cluster, and allows for radial variations in M/L. We bin the individual measurements on the plane of the sky to search efficiently through the parameter space of the models. Tests on an analytic model demonstrate that this approach is capable of measuring the cluster distance to an accuracy of about 6 per cent. Application to w Cen reveals no dynamical evidence for a significant radial dependence of M/L, in harmony with the relatively long relaxation time of the cluster. The best-fit dynamical model has a stellar V-band mass-to-light ratio M/L V = 2.5 ±0.1 M ○. /L ○. and an inclination i = 50° ± 4°, which corresponds to an average intrinsic axial ratio of 0.78 ± 0.03. The best-fit dynamical distance D = 4.8 ± 0.3 kpc (distance modulus 13.75 ± 0.13 mag) is significantly larger than obtained by means of simple spherical or constant-anisotropy axisymmetric dynamical models, and is consistent with the canonical value 5.0 ± 0.2 kpc obtained by photometric methods. The total mass of the cluster is (2.5 ± 0.3) x 10 6 M ○. . The best-fit model is close to isotropic inside a radius of about 10 arcmin and becomes increasingly tangentially anisotropic in the outer region, which displays significant mean rotation. This phase-space structure may well be caused by the effects of the tidal field of the Milky Way. The cluster contains a separate disk-like component in the radial range between 1 and 3 arcmin, contributing about 4% to the total mass.

Subfields: Astronomy and Astrophysics, Computational Mechanics

View Paper: https://www.semanticscholar.org/paper/712916c34c6aded12bd9e0c1993ca973e4e3b586

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Citations in the corpus

THE NUCLEUS OF THE SAGITTARIUS DSPH GALAXY AND M54: A WINDOW ON THE PROCESS OF GALAXY NUCLEATION (2008, methodology): “Rotation We searched for signal of rotation in the two samples, also taking into account the correction for perspective rotation, according to van de Ven et al. (2006) and taking the proper motion of Sgr/M54 from Dinescu et al. (2005); in the present case the absolute value of the maximum…”
Mean proper motions, space orbits, and velocity dispersion profiles of Galactic globular clusters derived fromGaiaDR2 data (2018, background): “We did not correct for perspective effects (e.g. van de Ven et al. 2006) since these are usually less than 0.1 km/sec, i.e. significantly smaller than the cluster velocity dispersions themselves.”
A geometric distance measurement to the Galactic center black hole with 0.3% uncertainty (2019, methodology): “The measurement is direct because this can be done for individual stellar orbits, as opposed to using a sample of stars together with a dynamical model like in van de Ven et al. (2006) for the globular cluster ω Cen or in Chatzopoulos et al. (2015) for the Milky Way nuclear cluster.”
N-body modelling of globular clusters: masses, mass-to-light ratios and intermediate-mass black holes (2016, methodology): “Sources for velocity and surface density data used in this work (LOS = line-of-sight radial velocities, PM = proper motion velocity dispersion profile, IFU = Integral field unit velocity dispersion, SD = surface density profile) Name Source Type NGC 104 Mayor et al. (1983) LOS Gebhardt et al. (1995)”
CHEMICAL ABUNDANCES FOR 855 GIANTS IN THE GLOBULAR CLUSTER OMEGA CENTAURI (NGC 5139) (2010, background): “The apparent suppression of Type Ia SNe in ω Cen remains an open problem, but it may be at least partially tied to the cluster’s several Gyr relaxation time scale (e.g., van de Ven et al. 2006) and low (∼3–4”
THE QUENCHING OF THE ULTRA-FAINT DWARF GALAXIES IN THE REIONIZATION ERA (2014, background): “Because even the most massive globular clusters haveM/LV ratios consistent with little to no dark matter (e.g., Baumgardt et al. 2009; van de Ven et al. 2006; Bradford et al. 2012), the highM/LV in the UFDs 2 is one of the characteristics that marks them as galaxies, instead of star clusters,…”
MEASUREMENT OF THE RADIUS OF NEUTRON STARS WITH HIGH SIGNAL-TO-NOISE QUIESCENT LOW-MASS X-RAY BINARIES IN GLOBULAR CLUSTERS (2012, background): “• ωCen’s distance was measured in a dynamical study, dωCen = 4.8±0.3 kpc (van de Ven et al. 2006), and no other reference provides a distance with its measurement uncertainty.”
A population of gamma-ray emitting globular clusters seen with the Fermi Large Area Telescope (2010, unknown): “References to the distance estimates are: (1) McLaughlin et al. (2006); (2) van de Ven et al. (2006); (3) Beccari et al. (2006); (4) Moretti et al. (2009); (5) Ortolani et al. (2007); (6) Ortolani et al. (1994); (7) Rees & Cudworth (1991); (8) Chaboyer et al. (2000); (9) Lee & Carney (2006); (10)…”
Galaxy Masses: A Review (2013, unknown): “At the present, this can be done for nearby star clusters by including plane-of-sky velocities from stellar proper motions in the dynamical models (e.g. van de Ven et al. 2006; van den Bosch et al. 2006; van der Marel & Anderson 2010).”
NEW LIMITS ON AN INTERMEDIATE-MASS BLACK HOLE IN OMEGA CENTAURI. I. HUBBLE SPACE TELESCOPE PHOTOMETRY AND PROPER MOTIONS (2009, methodology): “This center is adopted by van de Ven et al. (2006) and Castellani et al. (2008).”
Triaxial orbit based galaxy models with an application to the (apparent) decoupled core galaxy NGC 4365 (2007, methodology): “…to measure the mass of the central black hole in galaxies (Gebhardt et al. 2003) and that proper motion kinematic observations can be used (van de Ven et al. 2006), provided that the models have sufficient internal freedom, e.g. the total number of orbits is large enough (Cretton & Emsellem…”
The Multiplicity of the Subgiant Branch of ω Centauri: Evidence for Prolonged Star Formation (2007, methodology): “The luminosityL/L was derived from the apparent magnitude Vmeasured inWFI images, assuming the absolute distance modulus (m M )0 ¼ 13:75 found by van de Ven et al. (2006) and the reddening adopted above.”