Crescenzo Tortora, Aaron J. Romanowsky, Nicola R. Napolitano
Given a flurry of recent claims for systematic variations in the stellar initial mass function (IMF), we carry out a novel inventory of the observational evidence using different approaches. This includes literature results, as well as our own new findings from combined stellar-populations synthesis (SPS) and Jeans dynamical analyses of data on ~4500 early-type galaxies from the SPIDER project. We focus on the mass-to-light ratio mismatch relative to the Milky Way IMF, delta_IMF, correlated against the central stellar velocity dispersion, sigma_*. For the SPIDER sample, we find a strong correlation between delta_IMF and sigma_*, independently of assumptions on the dark matter (DM) profile. The overall normalization of delta_IMF, and the detailed DM profile, are less certain, but the data are consistent with standard cold-DM halos, and a central DM fraction that is roughly constant with sigma_*. For a variety of related studies in the literature, using SPS, dynamics, and gravitational lensing, similar results are found. Studies based solely on spectroscopic line diagnostics agree on a Salpeter-like IMF at high sigma_*, but differ at low sigma_*. Overall, we find that multiple independent lines of evidence appear to be converging on a systematic variation in the IMF, such that high-sigma_* early-type galaxies have an excess of low-mass stars relative to spirals and low-sigma_* early-types. Robust verification of super-Salpeter IMFs in the highest-sigma_* galaxies will require additional scrutiny of scatter and systematic uncertainties. The combined implications for the distribution of DM are still inconclusive.
View original:
http://arxiv.org/abs/1207.4475
No comments:
Post a Comment