Towards a fully consistent Milky Way disk model

Abstract

Aims. We present an updated version of the semi-analytic Just-Jahrei (JJ) model of the Galactic disk and constrain its parameters in the Solar neighbourhood. Methods. The new features of the JJ model include a simple two-component gaseous disk, a star-formation rate (SFR) function of the thick disk that has been extended in time, and a correlation between the kinematics of molecular gas and thin-disk populations. Here, we study the vertical number density profiles and W-velocity distributions determined from ∼2 × 106 local stars of the second Gaia data release (DR2). We also investigate an apparent Hess diagram of the Gaia DR2 stars selected in a conic volume towards the Galactic poles. Using a stellar evolution library, we synthesise stellar populations with a four-slope broken power-law initial mass function, the SFR, and an age-metallicity relation. The latter is consistently derived with the observed metallicity distribution of the local Red Clump giants from the Apache Point Observatory Galactic Evolution Experiment (APOGEE). Working within a Bayesian approach, we sample the posterior probability distribution in a multidimensional parameter space using the Markov chain Monte Carlo method. Results. We find that the spatial distribution and motion of the Gaia DR2 stars imply two recent SF bursts centered at ages of ∼0.5 Gyr and ∼3 Gyr and characterised by a ∼30% and ∼55% SF enhancement, respectively, relative to a monotonously declining SFR continuum. The stellar populations associated with this SF excess are found to be dynamically hot for their age: they have W-velocity dispersions of ∼12.5 km s−1 and ∼26 km s−1. The new JJ model is able to reproduce the local star counts with an accuracy of ∼5%. Conclusions. Using Gaia DR2 data, we self-consistently constrained 22 parameters of the updated JJ model. Our optimised model predicts two SF bursts within the last ∼4 Gyr, which may point to recent episodes of gas infall.

Stellar migration and chemical enrichment in the milky way disc: a hybrid model

“…More complex scenarios such as multiple bursts induced by repeated satellite passages (e.g. Lian et al 2020a,b;Ruiz-Lara et al 2020;Sysoliatina & Just 2021) or the onset of star formation occurring later in the outer disc to better capture the radial growth of the Galaxy (e.g. Frankel et al 2019) can be explored easily using VICE, but we do not explore such models here.…”

“…Other authors have suggested multiple bursts in the Milky Way's SFH (e.g. Lian et al 2020a,b;Ruiz-Lara et al 2020;Sysoliatina & Just 2021), perhaps triggered by satellite interactions, while others have advocated a two-phase SFH to explain the [α/Fe] dichotomy (e.g. Chiappini, Matteucci & Gratton 1997;Haywood et al 2016;Mackereth et al 2018;Spitoni et al 2019;Buck et al 2020;Khoperskov et al 2021).…”

Stellar Migration and Chemical Enrichment in the Milky Way Disc: A Hybrid Model

“…More complex scenarios with multiple bursts induced by repeated satellite passages (e.g. Lian et al 2020a,b;Ruiz-Lara et al 2020;Sysoliatina & Just 2021) can be modeled easily in VICE, but we do not explore them here.…”

“…Motivated by the observational analyses of Isern (2019) and Mor et al (2019), we also consider models with a burst of star formation centred ≈ 2 Gyr in the past, similar to the one-zone models investigated by Johnson & Weinberg (2020). Other authors have suggested multiple bursts in the Milky Way's SFH (e.g., Lian et al, 2020a,b;Ruiz-Lara et al 2020;Sysoliatina & Just 2021), perhaps triggered by satellite interactions, while others have advocated a two-phase SFH to explain the [𝛼/Fe]dichotomy (e.g., Chiappini, Matteucci & Gratton 1997;Haywood et al 2016;Spitoni et al 2019;Buck et al 2020;Khoperskov et al 2021). We do not investigate these more complex SFHs here, but we plan to do so in future work.…”

Arm Tangents and the Spiral Structure of the Milky Way—The Age Gradient

“…The encounter between "SDG" and the Milky Way was confirmed around 540 M years ago [17]. Sysoliatina et al [18] were able to match their star model to the Gaia star data in the solar neighborhood, provided there were two bursts of star formation within the last 4 Gyrs. A recent model [19] argued that the "phase spiral" (V z versus z) was excited some 1 to 2 Gyrs before the recent transit of SDG.…”