Lorenzo Posti

A discrete chemo-dynamical model of the dwarf spheroidal galaxy Sculptor: mass profile, velocity anisotropy and internal rotation

We present a new discrete chemo-dynamical axisymmetric modelling technique, which we apply to the dwarf spheroidal galaxy Sculptor. The major improvement over previous Jeans models is that realistic chemical distributions are included directly in the dynamical modelling of the discrete data. This avoids loss of information due to spatial binning and eliminates the need for hard cuts to remove contaminants and to separate stars based on their chemical properties. Using a combined likelihood in position, metallicity and kinematics, we find that our models naturally separate Sculptor stars into a metal-rich and a metal-poor population. Allowing for non-spherical symmetry, our approach provides a central slope of the dark matter density of γ = 0.5 ± 0.3. The metal-rich population is nearly isotropic (with β _r^{red} = 0.0± 0.1), while the metal-poor population is tangentially anisotropic (with β _r^{blue} = -0.2± 0.1) around the half-light radius of 0.26 kpc. A weak internal rotation of the metal-rich population is revealed with vmax/σ0 = 0.15 ± 0.15. We run tests using mock data to show that a discrete data set with ˜6000 stars is required to distinguish between a core (γ = 0) and cusp (γ = 1), and to constrain the possible internal rotation to better than 1σ confidence with our model. We conclude that our discrete chemo-dynamical modelling technique provides a flexible and powerful tool to robustly constrain the internal dynamics of multiple populations, and the total mass distribution in a stellar system.

The power of teaming up HST and Gaia: the first proper motion measurement of the distant cluster NGC 2419

Aims: We present the first measurement of the proper motion and orbit of the very distant and intriguing globular cluster NCG 2419. Methods: We have combined data from HST and Gaia DR1 to derive the relative proper motions of stars in the direction to the cluster. To tie to an absolute reference frame we have used a background galaxy located in the field. Results: We find the absolute proper motion of NGC 2419 to be

Three-dimensional motions in the Sculptor dwarf galaxy as a glimpse of a new era

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The dynamically selected stellar halo of the Galaxy with Gaia and the tilt of the velocity ellipsoid

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Action-based dynamical models of dwarf spheroidal galaxies: application to Fornax

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Galaxy spin as a formation probe: the stellar-to-halo specific angular momentum relation

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Leafs on trees: identifying halo stars with extreme gradient boosted trees

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The angular momentum-mass relation: a fundamental law from dwarf irregulars to massive spirals

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Mass and shape of the Milky Way's dark matter halo with globular clusters from Gaia and Hubble

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Scratching the surface with TGAS and RAVE: disk moving groups in the Solar neighborhood

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