Document Type


Publication Date

November 2017

Publication Title

The Astrophysical Journal Letters



Issue Number





galaxies: star formation, galaxies: stellar content, galaxies: star clusters: general


Astrophysics and Astronomy | External Galaxies | Stars, Interstellar Medium and the Galaxy


Analyses of strong gravitational lenses, galaxy-scale kinematics, and absorption-line stellar population synthesis (SPS) have all concluded that the stellar initial mass function (IMF) varies within the massive early-type galaxy (ETG) population. However, the physical mechanism that drives variation in the IMF is an outstanding question. Here we use new SPS models to consider a diverse set of compact, low-velocity dispersion stellar systems: globular clusters (GCs), an ultra-compact dwarf (UCD), and the compact elliptical (cE) galaxy M32. We compare our results to massive ETGs and available dynamical measurements. We find that the GCs have stellar mass-to-light ratios (M/L) that are either consistent with a Kroupa IMF or are slightly bottom-light, while the UCD and cE have mildly elevated M/L. The separation in derived IMFs for systems with similar metallicities and abundance patterns indicates that our SPS models can distinguish abundance and IMF effects. Variation among the sample in this paper is only ~50% in normalized M/L compared to the ~4X among the ETG sample. This suggests that metallicity is not the sole driver of IMF variability and additional parameters need to be considered.


This article was originally published in The Astrophysical Journal Letters, volume 850, issue 1. © 2017. The American Astronomical Society. All rights reserved.
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