Towards a fully consistent Milky Way disc model: Part 1 The local model based on kinematic and photometric data

TL;DR

This paper develops a comprehensive model of the Milky Way's local disc, integrating stellar populations, kinematic data, and chemical evolution to better understand its structure and history.

Contribution

It introduces a fully consistent evolutionary disc model based on star formation history, kinematic data, and chemical enrichment, constrained by Hipparcos observations.

Findings

The age-velocity dispersion relation is well constrained by local kinematics.

The star formation rate peaked 10 Gyr ago and declined to current levels.

An isothermal thick disc with ~6% local density is consistent with observations.

Abstract

We present a fully consistent evolutionary disc model of the solar cylinder. The model is based on a sequence of stellar sub-populations described by the star formation history (SFR) and the dynamical heating law (given by the age-velocity dispersion relation AVR). The combination of kinematic data from Hipparcos and the finite lifetimes of main sequence (MS) stars enables us to determine the detailed vertical disc structure independent of individual stellar ages and only weakly dependent on the IMF. The disc parameters are determined by applying a sophisticated best fit algorithm to the MS star velocity distribution functions in magnitude bins. We find that the AVR is well constrained by the local kinematics, whereas for the SFR the allowed range is larger. A simple chemical enrichment model is included in order to fit the local metallicity distribution of G dwarfs. In our favoured model A the power law index of the AVR is 0.375 with a minimum and maximum velocity dispersion of 5.1 km/s and 25.0 km/s, respectively. The SFR shows a maximum 10 Gyr ago and declines by a factor of four to the present day value of 1.5 M_sun/pc^2/Gyr. A best fit of the IMF leads to power-law indices of -1.46 below and -4.16 above 1.72 M_sun avoiding a kink at 1 M_sun. An isothermal thick disc component with local density of ~6% of the stellar density is included. A thick disc containing more than 10% of local stellar mass is inconsistent with the local kinematics of K and M dwarfs.