News and Highlights

The extended PN.S Early-Type galaxy project: Probing halo kinematics with Planetary Nebulae

The current understanding of the formation scenario for early type galaxies (ETGs) is that it proceeds in two phases: an initial fast assembly stage, in which galaxies form in-situ stars, followed by a phase dominated by the hierarchical accretion of smaller galaxies, whose stars mainly deposit in the halos. Because of the different origin of the halos with respect to the central regions, ETGs are expected to have different kinematic properties at large radii than at the centers. The extended PN Spectrograph (ePN.S) survey is the largest survey to-date of ETG kinematics with PNe.

Pulsoni, C., Gerhard, O., Arnaboldi, M., et al., 2018, A&A, 618, A94 more

Echo of the bar buckling: Phase space spirals

Since the publication of its second catalog, ESA's Gaia mission has been making new discoveries about the movement of stars in our Galaxy and its dynamic state. One of the most striking discoveries concerns the existence of spiral structures in z-Vz phase space. This has so far been interpreted as due to a state of non-equilibrium in our galaxy. Using an extremely high-resolution N-body simulation (N=141 million particles) we explore an alternative scenario of formation, evolution and spatial variation of the phase-space spirals similar to those recently discovered in Gaia DR2.

Khoperskov, S., Di Matteo, P., Gerhard, O., et al., 2019, A&A, 622, L6
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The Milky Way bar/bulge in proper motions: a 3D view from VIRAC & Gaia

Recent ground based Infrared surveys have provided an unprecedented view on the bulge of the Milky Way. The Vista Variable in the Via Lactea Survey has recently provided a 300 square degree view of the Galactic bulge over a 5 year observational period. Proper motions derived from this, when combined with the astonishing astrometric properties of the ESA's Gaia satellite, provide an opportunity to study the dynamical structure of the bar like never before.

Jonathan Clarke, Christopher Wegg, Ortwin Gerhard et al., 2019, arXiv:1903.02003

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The Milky Way's Gravitational Force Field Measured from RR Lyrae in Gaia

The Gaia satellite has measured proper motions (meaning the motion across the sky) for more than a billion stars across the Galaxy. However, unfortunately for most of these stars we do not have the distances we need to turn these proper motions into velocities. RR Lyrae are a type of variable star where we can estimate accurate distances. We have therefore used a sample of almost 16,000 RR Lyrae measured by Gaia to measure the dynamics of the stars which make up the Milky Way's stellar halo.

Christopher Wegg, Ortwin Gerhard and Marie Bieth, 2019, MNRAS, 485, 3296

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