Isochrone ages for ∼3 million stars with the second Gaia data release

Abstract

We present a catalogue of distances, masses and ages for ∼ 3 million stars in the second Gaia data release with spectroscopic parameters available from the large spectroscopic surveys: APOGEE, Gaia-ESO, GALAH, LAMOST, RAVE and SEGUE. We use a Bayesian framework to characterise the probability density functions of distance, mass and age using photometric, spectroscopic and astrometric information, supplemented with spectroscopic masses where available for giant stars. Furthermore, we provide posterior extinction estimates (A V ) to every star using published extinction maps as a prior input. We provide an appendix with extinction coefficients for Gaia photometry derived from stellar models, which account for variation with intrinsic colour and total extinction. Our pipeline provides output estimates of the spectroscopic parameters, which can be used to inform improved spectroscopic analysis. We complement our catalogues with Galactocentric coordinates and actions with associated uncertainties. As a demonstration of the power of our catalogue, we produce velocity dispersion profiles of the disc separated by age and Galactocentric radius (between 3 and 15 kpc from the Galactic centre). This suggests that the velocity dispersion profiles flatten with radius in the outer Galaxy (> 8 kpc) and that at all radii the velocity dispersion follows the smooth power law with age observed in the solar neighbourhood.

The Splash without a Merger

“…As described in Section 2, our simulation self-consistently evolves as an isolated Figure 1. Left column shows the MW stars with 0.5 < |z|/kpc < 3 from Sanders & Das (2018). The simulation panels are for stars with 5 < R/kpc < 11 and |z| < 3 kpc, see details in the text.…”

“…We also note, by analysing the simulation snapshots, that this old population is already kinematically hot in the first 3 Gyrs of the simulation. Therefore, internal dynamical heating in a MW-like galaxy is enough to heat the primordial disk in its early stages and produce 7 We select stars in Sanders & Das (2018) with estimated age error lower than 2 Gyrs.…”

“…In particular, Di Matteo et al (2019) noted a low angular momentum population with thick disk chemistry (see, e.g., their figure 13) and proposed that the classical Milky Way (MW) inner-halo is actually composed of two stellar populations: i) heated stars from the thick disk (referred by them as the "Plume"), where the heating mechanism is associated with a major merger event named the Gaia-Sausage/Enceladus 1 (Belokurov et al 2018;Helmi et al 2018); ii) accreted stars from the Gaia-Sausage. Belokurov et al (2019) (hereafter B19 ), using the Sanders & Das (2018) catalogue, disentangled the aforementioned low angular momentum structure from the canonical thick disk and stellar halo. They suggested 2 Amarante et al that this structure, which they termed the Splash, is chemically and dynamically distinct from the known stellar populations in our Galaxy.…”

The GALAH survey: temporal chemical enrichment of the galactic disc

“…Here A S is taken from Schlegel et al (1998). We furthermore force the sampled parallax (ω sample ) to be positive.…”

“…However they often have only relatively small samples of stars (up to ∼ 10 3 stars, e.g., Adibekyan et al 2012;Haywood et al 2013), and usually do not account for their heterogeneous selection effects. Only very recently has isochrone ages of large samples of stars (∼ 10 5 stars) become available (e.g., Mints & Hekker 2018;Queiroz et al 2018;Sanders & Das 2018), this is coupled with the data releases of large scale spectroscopic surveys such as GALAH (De Silva et al 2015;Buder et al 2018), LAMOST (Luo et al 2015), APOGEE (Holtzman et al 2015), Gaia-ESO (Gilmore et al 2012) and parallax information from Gaia (Gaia Collaboration et al 2018). The large number of stars covered by these surveys make separation of different galactic components and populations more achievable.…”