Hitting the Bull's-eye: The Radial Profile of Accretion and Star Formation in the Milky Way

TL;DR

This study compares dwarf galaxy accretion and halo gas cooling as sources of gas for star formation in the Milky Way, finding halo cooling better explains the observed central concentration of star formation.

Contribution

It demonstrates that direct halo gas cooling, not dwarf galaxy accretion, accounts for the radial distribution of star formation in the Milky Way.

Findings

Dwarf galaxy accretion cannot reproduce the central concentration of star formation.

Halo gas cooling matches the observed radial profile of star formation.

Difference attributed to angular momentum discrepancies.

Abstract

Ongoing star formation in the Milky Way requires continuous gaseous fuel from accretion. Previous work has suggested that the accretion of dwarf galaxies could provide the needed gas for this process. In this work we investigate whether dwarf galaxy accretion is consistent with the radial profile of star formation observed in the Milky Way, which is strongly concentrated toward the center of the gaseous disk of the Galaxy. Using realistic parameters for the Galactic potential, gaseous halo, Galactic disk, velocities of dwarf galaxies, and effects of drag on stripped gas in the halo, we model the distribution of radii at which dwarf galaxies accrete onto the Galactic disk. We also model the radial distribution of the accretion of gas that cools directly out of the halo by examining the results of recent simulations. We show that dwarf galaxies cannot reproduce the concentration of accretion toward the center of the Galaxy required by star formation. We also show that clouds that cool directly from the halo can reproduce this central concentration, and conclude that this difference is largely due to the discrepancy in absolute specific angular momentum between the two mechanisms.