Star Formation History of the Local Group Dwarf Irregular Galaxy, NGC 6822

TL;DR

This study reconstructs the star formation history of NGC 6822, a dwarf irregular galaxy, using evolved AGB stars and infrared data, revealing bursts of star formation around 2.6-2.9 Gyr ago and recent activity in the bar region.

Contribution

Introduces a novel method utilizing evolved AGB stars and infrared data to trace the star formation history of NGC 6822, extending analysis beyond the optical body.

Findings

Significant star formation burst around 2.6-2.9 Gyr ago.

Enhanced star formation activity in the past 200 Myr in the bar region.

Star formation history differs between the central bar and outer regions.

Abstract

NGC 6822 is an isolated dwarf irregular galaxy in the local group at a distance of 490 kpc. In this paper, we present the star formation history (SFH) within a field with a radius of 3 kpc, beyond the optical body of the galaxy (1.2 kpc). We utilized a novel method based on evolved asymptotic giant branch (AGB) stars. We collected the Near infrared data of 329 variable stars, including long-period and amplitude variables and Carbon-rich AGB stars. We used stellar evolutionary track and theoretical isochrones to obtain the birth mass, age, and pulsation duration of the detected stars to calculate the star formation rate (SFR) and trace the SFH of the galaxy. We studied the star formation history of the galaxy for the mean metallicity value (Z) of 0.003. We reconstructed the SFH for two regions. The bar region, a central rectangular area, and the outer region, which covers a circular field beyond the bar region and extends to a radius of 3 kpc. Our results show a significant burst of star formation around 2.6 and 2.9 Gyr ago in the bar and outer regions, respectively. Additionally, we observed a notable enhancement in the SFR in the bar region over the past 200 Myr.