Stellar Velocity Profiles and Line-Strengths out to Four Effective Radii in the Early-Type Galaxy NGC 3379

TL;DR

This paper introduces a new method using SAURON to measure stellar kinematics and line-strengths at large radii in NGC 3379, revealing dark matter presence and radial gradients in line strengths.

Contribution

The study presents a novel technique for measuring stellar properties at large radii and applies it to NGC 3379, demonstrating dark matter detection and consistent line-strength gradients.

Findings

Approximately 40% of mass within 5 Re is dark matter.

Radial gradients in line-strengths are constant out to 4 Re.

New measurement technique effective at large galactic radii.

Abstract

We describe a new technique to measure stellar kinematics and line-strengths at large radii in nearby galaxies. Using the integral-field spectrograph SAURON as a 'photon-collector', we obtain spectra out to four effective radii (Re) in the early-type galaxy NGC 3379. By fitting orbit-based models to the extracted stellar velocity profile, we find that ~40% of the total mass within 5 Re is dark. The measured absorption line-strengths reveal a radial gradient with constant slope out to 4 Re.