The SAMI -- Fornax Dwarfs Survey I: Sample, observations and the specific stellar angular momentum of dwarf elliptical galaxies

TL;DR

This study uses deep integral field observations of dwarf elliptical galaxies in the Fornax cluster to measure their stellar angular momentum, revealing a decrease in rotation with lower mass and insights into their formation processes.

Contribution

First measurement of specific stellar angular momentum in the lowest mass dwarf ellipticals, linking their kinematics to galaxy formation mechanisms.

Findings

$ m ext{lambda}_R$ decreases with stellar mass

Higher proportion of slow rotators at lower masses

Consistent with dynamical heating in galaxy evolution

Abstract

Dwarf ellipticals are the most common galaxy type in cluster environments, however the challenges associated with their observation mean their formation mechanisms are still poorly understood. To address this, we present deep integral field observations of a sample of 31 low-mass ($10^{7.5} <$ M$_\star < 10^{9.5}$ M$_\odot$) early-type galaxies in the Fornax cluster with the SAMI instrument. For 21 galaxies our observations are sufficiently deep to construct spatially resolved maps of the stellar velocity and velocity dispersion - for the remaining galaxies we extract global velocities and dispersions from aperture spectra only. From the kinematic maps we measure the specific stellar angular momentum $\lambda_R$ of the lowest mass dE galaxies to date. Combining our observations with early-type galaxy data from the literature spanning a large range in stellar mass, we find that $\lambda_R$ decreases towards lower stellar mass, with a corresponding increase in the proportion of slowly rotating galaxies in this regime. The decrease of $\lambda_R$ with mass in our sample dE galaxies is consistent with a similar trend seen in somewhat more massive spiral galaxies from the CALIFA survey. This suggests that the degree of dynamical heating required to produce dEs from low-mass starforming progenitors may be relatively modest, and consistent with a broad range of formation mechanisms.