Rapid early gas accretion for the inner Galactic disc

Abstract

Recent observations of the Milky Way and galaxies at high redshifts suggest that galaxy discs were already in place soon after the Big Bang. While the gas infall history of the Milky Way in the inner disc has long been assumed to be characterised by a short accretion time scale, this has not been directly constrained using observations. Using the unprecedented amount and quality of data of the inner regions of the Milky Way that has recently been produced by APOGEE and Gaia, we aim to derive strong constraints on the infall history of the inner (less than 6 kpc) Galaxy (with a focus on stars between 4-6 kpc, which we show is an appropriate proxy for the entire inner disc). We have implemented gas infall into a chemical evolution model of the Galaxy disc, and used a Schmidt-Kennicutt law to connect the infall to the star formation. We explore a number of models, and two different formulations of the infall law. In one formulation, the infall is non-parametric, and in the other the infall has an explicitly exponential form. We fit the model parameters to the time-[Si/Fe] distribution of solar vicinity stars, and the metallicity and [Si/Fe] distribution function of stars with a galactocentric radius between 4-6 kpc from APOGEE. Our results point to a fast early gas accretion, with an upper limit of accretion timescale of around 2 Gyr in the inner disc of the Milky Way. This suggests that at least half the baryons were in place within 2-3 Gyr of the Big Bang, and that half the stars of the inner disc formed within the first 5 Gyr, during the thick disc formation phase. This implies that the stellar mass of the inner disc is dominated by the thick disc, supporting our previous work, and that the gas accretion onto the inner disc was rapid and early.

23 pages, 17 figures, 4 tables, submitted to A&A

References in corpus (18)

• Array Programming with NumPy
• The Gaia mission
• Cold streams in early massive hot haloes as the main mode of galaxy formation
• galpy: A Python Library for Galactic Dynamics
• A Highly Consistent Framework for the Evolution of the Star-Forming "Main Sequence" from z~0-6
• The APOGEE red-clump catalog: Precise distances, velocities, and high-resolution elemental abundances over a large area of the Milky Way's disk
• A First Constraint on the Thick Disk Scale Length: Differential Radial Abundances in K Giants at Galactocentric Radii 4, 8, and 12 kpc
• Chemical abundances of 1111 FGK stars from the HARPS GTO planet search program II: Cu, Zn, Sr, Y, Zr, Ba, Ce, Nd and Eu
• Tracing chemical evolution over the extent of the Milky Way's Disk with APOGEE Red Clump Stars
• Reconstructing the star formation history of the Milky Way disc(s) from chemical abundances
• A Cold, Massive, Rotating Disk Galaxy 1.5 Billion Years after the Big Bang
• Bar quenching in gas-rich galaxies
• The Pristine survey X: a large population of low-metallicity stars permeates the Galactic disk
• Quantifying stellar radial migration in an N-body simulation: blurring, churning, and the outer regions of galaxy discs
• Revisiting long-standing puzzles of the Milky Way: the Sun and its vicinity as typical outer disk chemical evolution
• Hic sunt dracones: Cartography of the Milky Way spiral arms and bar resonances with Gaia Data Release 2
• Radial structure and formation of the Milky Way disc
• Automated bar detection in local disc galaxies from the SDSS - The colors of bars