Identification of the long stellar stream of the prototypical massive globular cluster ω Centauri

Abstract

Omega Centauri (ω Cen) is the Milky Way’s most massive globular cluster, and has long been suspected of being the remnant core of an accreted dwarf galaxy. If this scenario is correct, ω Cen should be tidally limited and tidal debris should be spread along its orbit. Here we use N-body simulations to show that the recently discovered ‘Fimbulthul’ structure is the long-sought-for tidal stream of ω Cen, extending up to 28° from the cluster. Follow-up high-resolution spectroscopy of five stream stars shows that they are closely grouped in velocity, and have metallicities consistent with having originated in that cluster. Informed by our N-body simulations, we devise a selection filter that we apply to Gaia mission data to also uncover the stream in the highly contaminated and crowded field within 10° of ω Cen. Further modelling of the stream may help to constrain the dynamical history of the dwarf galaxy progenitor of this disrupting system and guide future searches for its remnant stars in the Milky Way.

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Fig. 1: Physical properties of the Fimbulthul stream as a function of \(\ell\).
Fig. 2: Present-day configuration of an N-body simulation of the disruption of a massive globular cluster on the orbit of ω Cen.
Fig. 3: Comparison of the colour-magnitude diagram of ω Cen and Fimbulthul in the Gaia photometric system.
Fig. 4: Stars with kinematic properties of the expected stream near ω Cen, fulfilling colour and magnitude selection criteria.

Data availability

The Gaia DR2 data on which this study was based are available at https://www.cosmos.esa.int/web/gaia/dr2. The Fimbulthul stars shown in Fig. 1 are listed in Supplementary Table 1.

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Acknowledgements

This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. We thank the staff of the CFHT for taking the ESPaDOnS data used here, and for their continued support throughout the project. Based on observations obtained at the CFHT, which is operated by the National Research Council of Canada, the Institut National des Sciences de l’Univers of the Centre National de la Recherche Scientique of France and the University of Hawaii. This work has been published under the framework of the IdEx Unistra and benefits from a funding from the state managed by the French National Research Agency as part of the investments for the future programme. PyRAF is a product of the Space Telescope Science Institute, which is operated by AURA for NASA. R.A.I. and N.M. gratefully acknowledge support from a ‘Programme National Cosmologie et Galaxies’ grant.

Author information

All authors assisted in the development, analysis and writing of the paper. R.A.I., K.M. and N.M. devised the STREAMFINDER software that detected the Fimbulthul stream. M.B. analysed the Gaia mission data to reveal the presence of the stream close to ω Cen. The spectroscopic measurements were performed by R.A.I. The initial conditions for the dynamical model of ω Cen were developed by P.B.

Correspondence to Rodrigo A. Ibata.

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