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

Abstract

We study the dynamical properties of halo stars located in the Solar Neighbourhood. Our goal is to explore how the properties of the halo depend on the selection criteria used for defining a sample of halo stars. Once this is understood we proceed to measure the shape and orientation of the halo's velocity ellipsoid and we use this information to put constraints on the gravitational potential of the Galaxy. We use the recently released Gaia DR1 catalogue cross-matched to the RAVE dataset for our analysis. We develop a dynamical criterion based on the distribution function of stars in various Galactic components, using action integrals to identify halo members, and compare this to metallicity and to kinematically selected samples. With this new method, we find 1156 stars in the Solar Neighbourhood to be likely members of the stellar halo. Our dynamically selected sample consists mainly of distant giants on elongated orbits. Their metallicity distribution is rather broad, with roughly half of the stars having [M/H] $\ge -1$ dex. The use of different selection criteria has an important impact on the characteristics of the velocity distributions obtained. Nonetheless, for our dynamically selected and for the metallicity selected samples, we find the local velocity ellipsoid to be aligned in spherical coordinates in a Galactocentric reference frame: this suggests that the total gravitational potential is rather spherical in the region spanned by the orbits of the halo stars in these samples.

matches A&A published version

References in corpus (17)

• Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties
• The Radial Velocity Experiment (RAVE): first data release
• Two Stellar Components in the Halo of the Milky Way
• The Radial Velocity Experiment (RAVE): Fifth Data Release
• The Radial Velocity Experiment (RAVE): second data release
• The stellar halo of the Galaxy
• Constraining the Galaxy's dark halo with RAVE stars
• Estimating distances from parallaxes. II. Performance of Bayesian distance estimators on a Gaia-like catalogue
• A box full of chocolates: The rich structure of the nearby stellar halo revealed by Gaia and RAVE
• Estimation of the Tilt of the Stellar Velocity Ellipsoid from RAVE and Implications for Mass Models
• Action-based distribution functions for spheroidal galaxy components
• The first all-sky view of the Milky Way stellar halo with Gaia+2MASS RR Lyrae
• A centrally heated dark halo for our Galaxy
• Bringing the Galaxy's dark halo to life
• Does SEGUE/SDSS indicate a dual Galactic halo?
• Made-to-Measure Dark Matter Haloes, Elliptical Galaxies and Dwarf Galaxies in Action Coordinates
• Galactic googly: the rotation-metallicity bias in the inner stellar halo of the Milky Way

Cited by in corpus (33)

• The merger that led to the formation of the Milky Way's inner stellar halo and thick disk
• Co-formation of the Galactic disc and the stellar halo
• AGAMA: Action-based galaxy modelling architecture
• In disguise or out of reach: first clues about in-situ and accreted stars in the stellar halo of the Milky Way from Gaia DR2
• The GALAH survey and Gaia DR2: dissecting the stellar disc's phase space by age, action, chemistry and location
• Mass and shape of the Milky Way's dark matter halo with globular clusters from Gaia and Hubble
• Characterization and history of the Helmi streams with Gaia DR2
• The Gravitational Force Field of the Galaxy Measured From the Kinematics of RR Lyrae in Gaia
• Gaia and the Galactic Center Origin of Hypervelocity Stars
• GASTRO library I: the simulated chemodynamical properties of several GSE-like stellar halos
• Abundances and kinematics of carbon-enhanced metal-poor stars in the Galactic halo*; A new classification scheme based on Sr and Ba
• Constraints on the assembly history of the Milky Way's smooth, diffuse stellar halo from the metallicity-dependent, radially-dominated velocity anisotropy profiles probed with K giants and BHB stars using LAMOST, SDSS/SEGUE, and Gaia
• The Atari Disk, a Metal-Poor Stellar Population in the Disk System of the Milky Way
• The tale of the tail -- disentangling the high transverse velocity stars in Gaia DR2
• WISEA J041451.67-585456.7 and WISEA J181006.18-101000.5: The First Extreme T-type Subdwarfs?
• The stellar velocity distribution function in the Milky Way galaxy
• Chasing Accreted Structures within Gaia DR2 using Deep Learning
• Phase-space Properties and Chemistry of the Sagittarius Stellar Stream Down to the Extremely Metal-poor ($[Fe/H]\lesssim -3$) Regime
• Targeting Bright Metal-poor Stars in the Disk and Halo Systems of the Galaxy
• Cataloging Accreted Stars within Gaia DR2 using Deep Learning
• Probing the Galactic halo with RR Lyrae stars $-$ III. The chemical and kinematic properties of the stellar halo
• The tilt of the velocity ellipsoid in the Milky Way with Gaia DR2
• Milky Way Subsystems from Globular Clusters Kinematics Using Gaia DR2 and HST Data
• The relative efficiencies of bars and clumps in driving disc stars to retrograde motion
• Frequencies, chaos and resonances: a study of orbital parameters of nearby thick disc and halo stars
• The Reduced Proper Motion selected halo: methods and description of the catalogue
• Existence of the Metal-Rich Stellar Halo and High-velocity Thick Disk in the Galaxy
• Leaves on trees: identifying halo stars with extreme gradient boosted trees
• Element abundance analysis of the metal-rich stellar halo and high-velocitythick disk in the galaxy
• Two substructures in the nearby stellar halo found in Gaia and RAVE
• Searching For Transiting Planets Around Halo Stars. I. Sample Selection and Validation
• OGLE-2017-BLG-1038: A Possible Brown-dwarf Binary Revealed by Spitzer Microlensing Parallax
• New families in our Solar neighborhood: applying Gaussian Mixture models for objective classification of structures in the Milky Way and in simulations