Kinematics of the local disk from the RAVE survey and the Gaia first data release

Abstract

Aims. We attempt to constrain the kinematics of the thin and thick disks using the Besançon population synthesis model together with RAVE DR4 and Gaia first data release (TGAS). Methods. The RAVE fields were simulated by applying a detailed target selection function and the kinematics was computed using velocity ellipsoids depending on age in order to study the secular evolution. We accounted for the asymmetric drift computed from fitting a Stäckel potential to orbits. Model parameters such as velocity dispersions, mean motions, and velocity gradients were adjusted using an ABC-MCMC method. We made use of the metallicity to enhance the separation between thin and thick disks. Results. We show that this model is able to reproduce the kinematics of the local disks in great detail. The disk follows the expected secular evolution, in very good agreement with previous studies of the thin disk. The new asymmetric drift formula, fitted to our previously described Stäckel potential, fairly well reproduces the velocity distribution in a wide solar neighborhood. The U and W components of the solar motion determined with this method agree well with previous studies. However, we find a smaller V component than previously thought, essentially because we include the variation of the asymmetric drift with distance to the plane. The thick disk is represented by a long period of formation (at least 2 Gyr), during which, as we show, the mean velocity increases with time while the scale height and scale length decrease, very consistently with a collapse phase with conservation of angular momentum.Conclusions. This new Galactic dynamical model is able to reproduce the observed velocities in a wide solar neighborhood at the quality level of the TGAS-RAVE sample, allowing us to constrain the thin and thick disk dynamical evolution, as well as determining the solar motion.

The Dynamics of Interstellar Asteroids and Comets within the Galaxy: An Assessment of Local Candidate Source Regions for 1I/’Oumuamua and 2I/Borisov

“…These values are lower than are usually covered by galactic age-velocity relations, but imply an age less than 1 Gyr e.g. an extrapolation of (Holmberg et al 2009) Figure 7 yields an age ∼ 100 Myr; (Robin et al 2017) reports an age less than 150 Myr for the subcomponent corresponding to 'Oumuamua's velocity. Other authors have also argued 'Oumuamua's small deviation from the LSR indicates it has undergone only a small amount of dynamical perturbation throughout its journey (Gaidos et al 2017).…”

“…Such low velocities are indicative of young ∼ < 100 Myr stellar ages from standard age-velocity relations e.g. (Holmberg et al 2009;Robin et al 2017). The second part of the conjecture, that 'Oumuamua was ejected at low velocity relative to its parent system, is based on the higher efficiency of most ejection processes at launching material at lower speeds.…”

“…We draw stars which are bonafide or suspected members of each moving group from two sources. The principle source we use is the Catalog of Suspected Nearby Young Stars as supplied in Riedel et al (2018). This catalog is intended as 'a single resource for studying the individual and ensemble properties of young stars' ).…”

The 13th Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the SDSS-IV Survey Mapping Nearby Galaxies at Apache Point Observatory

“…RAVE's primary goal was to obtain spectroscopic measurements for stars with exquisite Gaia proper-motion and parallax measurements. The ∼250,000 stars in DR5 that have proper motions and parallaxes in the first Gaia data release (Gaia Collaboration et al 2016) now make this work possible in both the disk (e.g., Robin et al 2017) and halo (e.g., Helmi et al 2017). Among the many results published prior to the Gaia results were measurements of the local escape velocity (e.g., Smith et al 2007;Piffl et al 2014), detection of a "wobbly" galaxy from asymmetric velocities both radially and across the disk (Siebert et al 2011;Williams et al 2013), and the observation of extra-tidal stars from Galactic globular clusters (e.g., Kunder et al 2014;Fernández-Trincado et al 2015;Anguiano et al 2016).…”

The GALAH survey: velocity fluctuations in the Milky Way using Red Clump giants

“…It is thus important to have multiple methods to constrain the Solar motion about the Galactic centre. Robin et al (2017) take this forward by making use of highly accurate proper motions from Gaia data release 1 (Gaia Collaboration 2016) and RAVE-DR4 to model the asymmetric drift and leave the Solar motion as a free parameter. They propose a new, much lower value for V of 0.94 km s −1 , but again their analysis is only restricted to the Solar vicinity probing well within 2 kpc of the Sun with mean distances around 1 kpc.…”