DYNAMICAL VERSUS STELLAR MASSES IN COMPACT EARLY-TYPE GALAXIES: FURTHER EVIDENCE FOR SYSTEMATIC VARIATION IN THE STELLAR INITIAL MASS FUNCTION
- Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States)
- Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany)
- Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)
- Max-Planck-Institute for Extraterrestrial Physics, Giessenbachstrasse, D-85748 Garching (Germany)
- Department of Astrophysical Sciences, Yale University, New Haven, CT 06511 (United States)
Several independent lines of evidence suggest that the stellar initial mass function (IMF) in early-type galaxies becomes increasingly 'bottom-heavy' with increasing galaxy mass and/or velocity dispersion, σ. Here we consider evidence for IMF variation in a sample of relatively compact early-type galaxies drawn from the Sloan Digital Sky Survey. These galaxies are of sufficiently high stellar density that a dark halo likely makes a minor contribution to the total dynamical mass, M {sub dyn}, within one effective radius. We fit our detailed stellar population synthesis models to the stacked absorption line spectra of these galaxies in bins of σ and find evidence from IMF-sensitive spectral features for a bottom-heavy IMF at high σ. We also apply simple 'mass-follows-light' dynamical models to the same data and find that M {sub dyn} is significantly higher than what would be expected if these galaxies were stellar dominated and had a universal Milky Way IMF. Adopting M {sub dyn} ≈ M {sub *} therefore implies that the IMF is 'heavier' at high σ. Most importantly, the quantitative amount of inferred IMF variation is very similar between the two techniques, agreeing to within ∼< 0.1 dex in mass. The agreement between two independent techniques, when applied to the same data, provides compelling evidence for systematic variation in the IMF as a function of early-type galaxy velocity dispersion. Any alternative explanations must reproduce both the results from dynamical and stellar population-based techniques.
- OSTI ID:
- 22215426
- Journal Information:
- Astrophysical Journal Letters, Journal Name: Astrophysical Journal Letters Journal Issue: 2 Vol. 776; ISSN 2041-8205
- Country of Publication:
- United States
- Language:
- English
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