Dynamics in the outskirts of four Milky Way globular clusters: it's the tides that dominate by Zhen Wan et al. on Wednesday 30 November

We present the results of a spectroscopic survey of the outskirts of 4

globular clusters -- NGC 1261, NGC 4590, NGC 1904, and NGC 1851 -- covering

targets within 1 degree 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 individual 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 {\sc

limepy}/{\sc 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 {\sc limepy}/{\sc 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 {\sc limepy}/{\sc

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.

arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.16659v1