The Young Outer Disk of M83

TL;DR

Deep near-infrared imaging of M83's outer disk reveals a population of evolved stars, indicating ongoing star formation and providing insights into the galaxy's star formation history and cluster disruption timescales.

Contribution

This study presents the first detection and analysis of AGB stars in the outer disk of M83 using deep NICI images, linking stellar populations to galaxy evolution.

Findings

AGB stars are present outside known star clusters in M83's outer disk.

Star formation in the outer disk has continued over the past few Gyr.

Star formation activity occurred within the last 100 Myr, as indicated by red supergiants.

Abstract

Deep near-infrared images recorded with NICI on Gemini South are used to investigate the evolved stellar content in the outer regions of the south east quadrant of the spiral galaxy M83. A diffuse population of asymptotic giant branch (AGB) stars is detected outside of the previously identified young and intermediate age star clusters in the outer disk. The brightest AGB stars have M_K > -8, and the AGB luminosity function (LF) is well-matched by model LFs that assume ages < 1 Gyr. The specific star formation rate (SFR) during the past few Gyr estimated from AGB star counts is consistent with that computed from mid-infrared observations of star clusters at similar radii, and it is concluded that the disruption timescale for star clusters in the outer disk is << 1 Gyr. The luminosity function and specific frequency of AGB stars varies with radius, in a manner that is indicative of lower luminosity-weighted ages at larger radii. Modest numbers of red supergiants are also found, indicating that there has been star formation during the past 100 Myr, while the ratio of C stars to M giants is consistent with that expected for a solar metallicity system that has experienced a constant SFR for the past few Gyrs.