ORCID Profile
0000-0003-2927-5465
Current Organisation
Saint Mary's University
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Publisher: Oxford University Press (OUP)
Date: 26-04-2018
Publisher: Oxford University Press (OUP)
Date: 04-02-2021
Abstract: As part of a chemodynamical survey of five nearby globular clusters with 2dF/AAOmega on the Anglo-Australian Telescope (AAT), we have obtained kinematic information for the globular cluster NGC 3201. Our new observations confirm the presence of a significant velocity gradient across the cluster which can almost entirely be explained by the high proper motion of the cluster (${\\sim}9\\, \\mathrm{mas\\, yr^{-1}}$). After subtracting the contribution of this perspective rotation, we found a remaining rotation signal with an litude of ${\\sim}1\\, \\mathrm{km\\, s^{-1}}$ around a different axis to what we expect from the tidal tails and the potential escapers, suggesting that this rotation is internal and can be a remnant of its formation process. At the outer part, we found a rotational signal that is likely a result from potential escapers. The proper motion dispersion at large radii reported by Bianchini et al. ($3.5\\pm 0.9\\, \\mathrm{km\\, s^{-1}}$) has previously been attributed to dark matter. Here, we show that the LOS dispersion between 0.5 and 1 Jacobi radius is lower ($2.01\\pm 0.18\\, \\mathrm{km\\, s^{-1}}$), yet above the predictions from an N-body model of NGC 3201 that we ran for this study ($1.48\\pm 0.14\\, \\mathrm{km\\, s^{-1}}$). Based on the simulation, we find that potential escapers cannot fully explain the observed velocity dispersion. We also estimate the effect on the velocity dispersion of different amounts of stellar-mass black holes and unbound stars from the tidal tails with varying escape rates and find that these effects cannot explain the difference between the LOS dispersion and the N-body model. Given the recent discovery of tidal tail stars at large distances from the cluster, a dark matter halo is an unlikely explanation. We show that the effect of binary stars, which is not included in the N-body model, is important and can explain part of the difference in dispersion. We speculate that the remaining difference must be the result of effects not included in the N-body model, such as initial cluster rotation, velocity anisotropy, and Galactic substructure.
Publisher: Oxford University Press (OUP)
Date: 18-09-2023
Publisher: Oxford University Press (OUP)
Date: 22-04-2016
DOI: 10.1093/MNRAS/STW966
Publisher: Oxford University Press (OUP)
Date: 27-02-2021
Abstract: We present observations of the stellar kinematics of the centre of the core collapsed globular cluster M15 obtained with the MUSE integral field spectrograph on the Very Large Telescope operating in narrow field mode. Thanks to the use of adaptive optics, we obtain a spatial resolution of 0.1 arcsec and are able to reliably measure the radial velocities of 864 stars within 8 arcsec of the centre of M15, thus providing the largest s le of radial velocities ever obtained for the innermost regions of this system. Combined with previous observations of M15 using MUSE in wide field mode and literature data, we find that the central kinematics of M15 are complex with the rotation axis of the core of M15 offset from the rotation axis of the bulk of the cluster. While this complexity has been suggested by previous work, we confirm it at higher significance and in more detail.
Publisher: Oxford University Press (OUP)
Date: 08-12-2022
Abstract: We present the results of a spectroscopic survey of the outskirts of four globular – 1261, NGC 4590, NGC 1904, and NGC 1851 – covering targets within 1° from the cluster centres, with 2dF/AAOmega on the Anglo-Australian Telescope (AAT) and FLAMES on the very large telescope (VLT). We extracted chemo-dynamical information for in idual stars, from which we estimated the velocity dispersion profile and the rotation of each cluster. The observations are compared to direct N-body simulations and appropriate limepy/spes models for each cluster to interpret the results. In NGC 1851, the detected internal rotation agrees with existing literature, and NGC 1261 shows some rotation signal beyond the truncation radius, likely coming from the escaped stars. We find that the dispersion profiles for both the observations and the simulations for NGC 1261, NGC 1851, and NGC 1904 do not decrease as the limepy/spes models predict beyond the truncation radius, where the N-body simulations show that escaped stars dominate the dispersion profile of NGC 4590 follows the predictions of the limepy/spes models, though the data do not effectively extend beyond the truncation radius. The increasing/flat dispersion profiles in the outskirts of NGC 1261, NGC 1851, and NGC 1904, are reproduced by the simulations. Hence, the increasing/flat dispersion profiles of the clusters in question can be explained by the tidal interaction with the galaxy without introducing dark matter.
Publisher: Oxford University Press (OUP)
Date: 11-11-2021
Abstract: We report on the detection of a black hole (NGC 1850 BH1) in the ∼100-Myr-old massive cluster NGC 1850 in the Large Magellanic Cloud. It is in a binary system with a main-sequence turn-off star (4.9 ± 0.4 M⊙), which is starting to fill its Roche lobe and is becoming distorted. Using 17 epochs of Very Large Telescope/Multi-Unit Spectroscopic Explorer observations, we detected radial velocity variations exceeding 300 km s−1 associated with the target star, linked to the ellipsoidal variations measured by the fourth phase of the Optical Gravitational Lensing Experiment in the optical bands. Under the assumption of a semidetached system, the simultaneous modelling of radial velocity and light curves constrains the orbital inclination of the binary to 38° ± 2°, resulting in a true mass of the unseen companion of $11.1_{-2.4}^{+2.1}\\,{\\rm M}_{\\odot }$. This represents the first direct dynamical detection of a black hole in a young massive cluster, opening up the possibility of studying the initial mass function and the early dynamical evolution of such compact objects in high-density environments.
No related grants have been discovered for V. Hénault-Brunet.