Kavli Affiliate: Alexander P. Ji
| First 5 Authors: Petra Awad, Ting S. Li, Denis Erkal, Reynier F. Peletier, Kerstin Bunte
| Summary:
As globular clusters (GCs) orbit the Milky Way, their stars are tidally
stripped forming tidal tails that follow the orbit of the clusters around the
Galaxy. The morphology of these tails is complex and shows correlations with
the phase of the orbit and the orbital angular velocity, especially for GCs on
eccentric orbits. Here, we focus on two GCs, NGC 1261 and NGC 1904, that have
potentially been accreted alongside Gaia-Enceladus and that have shown
signatures of having, in addition of tidal tails, structures formed by
distributions of extra-tidal stars that are misaligned with the general
direction of the clusters’ respective orbits. To provide an explanation for the
formation of these structures, we make use of spectroscopic measurements from
the Southern Stellar Stream Spectroscopic Survey ($S^5$) as well as proper
motion measurements from Gaia’s third data release (DR3), and apply a Bayesian
mixture modeling approach to isolate high-probability member stars. We recover
extra-tidal features similar to those found in Shipp et al. (2018) surrounding
each cluster. We conduct N-body simulations and compare the expected
distribution and variation in the dynamical parameters along the orbit with
those of our potential member sample. Furthermore, we use Dark Energy Camera
(DECam) photometry to inspect the distribution of the member stars in the
color-magnitude diagram (CMD). We find that the potential members agree
reasonably with the N-body simulations and that the majority of them follow a
simple stellar population-like distribution in the CMD which is characteristic
of GCs. In the case of NGC 1904, we clearly detect the tidal debris escaping
the inner and outer Lagrange points which are expected to be prominent when at
or close to the apocenter of its orbit. Our analysis allows for further
exploration of other GCs in the Milky Way that exhibit similar extra-tidal
features.
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