Rotating stellar populations in the Fornax dSph galaxy

TL;DR

This study analyzes the internal kinematics of the Fornax dwarf spheroidal galaxy using a large spectroscopic dataset, revealing complex rotation patterns and suggesting a major merger event around redshift z~1.

Contribution

Introduces Beacon, a new software tool for detecting chemo-kinematic patterns, and applies it to uncover rotation signals and the galaxy's kinematic history.

Findings

Detection of significant rotation around main axes

Identification of multiple complex rotation patterns

Evidence supporting a major merger at redshift z~1

Abstract

We present a novel analysis of the internal kinematics of the Fornax dwarf spheroidal galaxy. Our results are based on the largest sample of spectroscopic data for Fornax stars presently available ($> 2500$ stars), for which we have chemical and kinematic information. We introduce new software, Beacon, designed to detect chemo-kinematic patterns among stars of different stellar populations using their metallicity and velocity along the line of sight. Applying Beacon to Fornax we have detected non-negligible rotation signals around main optical axes of the galaxy, characteristic for a triaxial system partially supported by rotation. The dominant rotation pattern is relatively strong ($\sim 12$ km s$^{-1}$), but the galaxy also shows additional weaker albeit complex rotation patterns. Using the information available from the star formation history of Fornax we have also derived the average age of the different chemo-kinematic components found by Beacon, which has allowed us to obtain its kinematic history. Our results point to a possible major merger suffered by Fornax at redshift $z\sim1$, in agreement with previous works.