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CG: Modelling the formation of the GD-1 stellar stream inside a host with a fermionic dark matter core-halo distribution. – Mestre

April 20 @ 12:45 pm 1:00 pm CMT

Stellar streams are a consequence of the tidal forces produced by a host galaxy on its satellites (i.e. globular clusters and dwarf spheroidals). As the self-gravity of stellar streams is almost negligible, they constitute excellent probes of the gravitational potential of the host galaxy. For this reason, some Milky Way stellar streams have been used to put constraints on the dark matter (DM) total mass and shape, under empirical DM distributions (i.e. NFW, logarithmic, etc). In particular, Malhan & Ibata (2019) have fitted the GD-1 orbit embedded in an axisymmetric NFW potential plus barions, obtaining that the density flattening of the dark halo is slightly oblate. In this work we consider an alternative DM model for the halo hosting GD-1, as previously deduced from first principles by means of the maximization of a coarse-grained entropy for self-gravitating fermions. Thanks to a self-consistent inclusion of the Pauli principle, the most general DM density profile out of this mechanism develops a degenerate compact core surrounded by a diluted halo which resembles the King profile. As recently shown, the latter is able to explain the galaxy rotation curves, while the dense DM core can mimic the central Black Hole (BH). Remarkably, we show that it is possible to model the GD-1 stellar stream with such a fermionic core-halo distribution, while at the same time the degenerate DM core lying at the center is in agreement with the orbits of the S-stars at Sagittarius A* without the need to assume a central BH. For this task we have used a genetic algorithm in order to fit both the stream orbit’s initial conditions and the fermionic halo. We modelled the barionic potential with a bulge and two disks (thin and thick) with fixed parameters according to the recent literature. The stream observable is 6D phase-space data from Ibata et al. (2020), including the Gaia DR2 survey.

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