Constraining the initial mass function of stars in the Galactic Centre

TL;DR

This study uses stellar evolution models to show that the observed properties of the Galactic Centre are consistent with a standard initial mass function, challenging previous suggestions of a top-heavy IMF due to extreme conditions.

Contribution

It demonstrates that a canonical IMF explains the luminosity, mass, and core structure of the Galactic Centre without requiring a top-heavy IMF, incorporating the role of stellar black holes.

Findings

Observed luminosity is too high for a long-standing top-heavy IMF.

A canonical IMF with continuous star formation matches the mass-to-light ratio.

Stellar black holes from a canonical IMF explain the core structure.

Abstract

(abridged) Here we discuss the question whether the extreme circumstances in the centre of the Milky Way may be the reason for a significant variation of the IMF. By means of stellar evolution models using different codes we show that the observed luminosity in the central parsec is too high to be explained by a long-standing top-heavy IMF, considering the limited amount of mass inferred from stellar kinematics in this region. In contrast, continuous star formation over the Galaxy's lifetime following a canonical IMF results in a mass-to-light ratio and a total mass of stellar black holes (SBHs) consistent with the observations. Furthermore, these SBHs migrate towards the centre due to dynamical friction, turning the cusp of visible stars into a core as observed in the Galactic Centre. For the first time here we explain the luminosity and dynamical mass of the central cluster and both the presence and extent of the observed core, since the number of SBHs expected from a canonical IMF is just enough to make up for the missing luminous mass. We conclude that the Galactic Centre is consistent with the canonical IMF and do not suggest a systematic variation as a result of the region's properties such as high density, metallicity, strong tidal field etc.