Star Formation History of Two Fields in the Halo of NGC5128

TL;DR

This study investigates the star formation history of two fields in NGC5128 using variable stars, revealing multiple star formation episodes and suggesting merger events and AGN activity influenced its evolution.

Contribution

The paper introduces a photometric method based on LPV and AGB stars to trace star formation history in NGC5128's halo fields, highlighting similarities and differences in their SFHs.

Findings

Three major star formation episodes at 800 Myr, 3.2 Gyr, and 10 Gyr ago.

Evidence of a merger around 800 Myr ago.

Lower recent star formation possibly driven by AGN activity and minor mergers.

Abstract

NGC5128 galaxy is a giant elliptical galaxy located in the Centaurus group of galaxies at 3.8 Mpc. We aim to study the star formation history (SFH) of two different fields of the galaxy. The northeastern field (Field 1) is located at a distance of 18.8 kpc, while the southern field (Field 2) is at 9.9 kpc. We use a photometric method that is based on identifying long period variable (LPV) stars and asymptotic giant branch (AGB) stars, as they are strong tracers of star formation and galaxy evolution due to their luminosity and variability; 395 LPVs in Field 1 and 671 LPVs in Field 2 have been identified. These two fields present similar SFHs, although the SF rate of Field 2 is more enhanced. We find that the galaxy has three major star formation episodes t $\sim$ 800 Myr ago, t $\sim$ 3.2 Gyr ago, and t $\sim$ 10 Gyr ago, where t is look-back time. The rate of star formation at $\sim$ 800 Myr ago agrees with previous studies suggesting that the galaxy experienced a merger around that time. Furthermore, NGC5128 has experienced a lower star formation rate in its recent history which could have been driven by jet-induction star formation and multiple outbursts of AGN activity in this galaxy, as well as a minor merger around 400 Myr ago.