IMF shape constraints from stellar populations and dynamics from CALIFA

TL;DR

This study uses stellar dynamics data from CALIFA to constrain the shape of the stellar initial mass function in early-type galaxies, ruling out single power law IMFs for most and supporting a double power law model with variable high-mass slope.

Contribution

It demonstrates how dynamical and stellar mass-to-light ratios can test and constrain the shape of the IMF in early-type galaxies, favoring a double power law model.

Findings

75% of galaxies exclude a single power law IMF shape.

95% of galaxies are compatible with a double power law IMF with a variable high-mass slope.

Dynamical and stellar IMF mismatch factors yield consistent results.

Abstract

In this letter we describe how we use stellar dynamics information to constrain the shape of the stellar IMF in a sample of 27 early-type galaxies from the CALIFA survey. We obtain dynamical and stellar mass-to-light ratios, $\Upsilon_\mathrm{dyn}$ and $\Upsilon_{\ast}$, over a homogenous aperture of 0.5~$R_{e}$. We use the constraint $\Upsilon_\mathrm{dyn} \ge \Upsilon_{\ast}$ to test two IMF shapes within the framework of the extended MILES stellar population models. We rule out a single power law IMF shape for 75% of the galaxies in our sample. Conversely, we find that a double power law IMF shape with a varying high-mass end slope is compatible (within 1$\sigma$) with 95% of the galaxies. We also show that dynamical and stellar IMF mismatch factors give consistent results for the systematic variation of the IMF in these galaxies.