Chemodynamical analysis of bulge stars for simulated disc galaxies

TL;DR

This study uses chemodynamical simulations to analyze the formation and characteristics of bulge stars in disc galaxies, revealing insights into their origins, merger history, and kinematic signatures.

Contribution

It introduces a chemodynamical analysis approach to distinguish accreted from in-situ bulge stars and links chemical signatures to merger events in galaxy evolution.

Findings

Accreted stars have high [alpha/Fe] and total energy.

Multiple mergers shape bulge formation with distinct chemical signatures.

Prograde rotation persists in stars formed during mergers.

Abstract

We analyse the kinematics and chemistry of the bulge stars of two simulated disc galaxies using our chemodynamical galaxy evolution code GCD+. First we compare stars that are born inside the galaxy with those that are born outside the galaxy and are accreted into the centre of the galaxy. Stars that originate outside of the bulge are accreted into it early in its formation within 3 Gyrs so that these stars have high [alpha/Fe] as well as having a high total energy reflecting their accretion to the centre of the galaxy. Therefore, higher total energy is a good indicator for finding accreted stars. The bulges of the simulated galaxies formed through multiple mergers separated by about a Gyr. Since [alpha/Fe] is sensitive to the first few Gyrs of star formation history, stars that formed during mergers at different epochs show different [alpha/Fe]. We show that the [Mg/Fe] against star formation time relation can be very useful to identify a multiple merger bulge formation scenario, provided there is sufficiently good age information available. Our simulations also show that stars formed during one of the merger events retain a systematically prograde rotation at the final time. This demonstrates that the orbit of the ancient merger that helped to form the bulge could still remain in the kinematics of bulge stars.