Evidence for a Long-Standing Top-Heavy IMF in the Central Parsec of the Galaxy

TL;DR

This study provides evidence that the initial mass function in the Galactic Center's central parsec has been consistently top-heavy over the last 12 billion years, based on deep spectroscopic data and star formation modeling.

Contribution

It presents the deepest spectroscopic analysis of the Galactic Center and demonstrates a long-standing top-heavy IMF through comparison with theoretical star formation models.

Findings

The IMF in the Galactic Center is top-heavy over 12 Gyr.

Deep spectroscopic data reaches the red clump magnitude.

Star formation has been continuous over the last 12 Gyr.

Abstract

We classify 329 late-type giants within 1 parsec of Sgr A*, using the adaptive optics integral field spectrometer SINFONI on the VLT. These observations represent the deepest spectroscopic data set so far obtained for the Galactic Center, reaching a 50% completeness threshold at the approximate magnitude of the helium-burning red clump (Ks ~ 15.5 mag.). Combining our spectroscopic results with NaCo H and Ks photometry, we construct an observed Hertzsprung-Russell diagram, which we quantitatively compare to theoretical distributions of various star formation histories of the inner Galaxy, using a chi-squared analysis. Our best-fit model corresponds to continuous star formation over the last 12 Gyr with a top-heavy initial mass function (IMF). The similarity of this IMF to the IMF observed for the most recent epoch of star formation is intriguing and perhaps suggests a connection between recent star formation and the stars formed throughout the history of the Galactic Center.