A Spitzer IRAC Census of the Asymptotic Giant Branch Populations in Local Group Dwarfs. II. IC 1613

TL;DR

This study uses Spitzer IRAC data to analyze the AGB star populations in the dwarf galaxy IC 1613, revealing limitations of optical surveys and estimating the galaxy's total AGB mass-loss rate.

Contribution

It provides the first comprehensive IRAC-based census of AGB stars in IC 1613, highlighting the importance of infrared observations for complete stellar population analysis.

Findings

Optical data detect less than half of the AGB population.

Infrared observations reveal a significant number of obscured AGB stars.

Estimated mass-loss rate from AGB stars is 0.2-1.0 x 10^(-3) solar masses per year.

Abstract

We present Spitzer Space Telescope IRAC photometry of the Local Group dwarf irregular galaxy IC 1613. We compare our 3.6, 4.5, 5.8, and 8.0 micron photometry with broadband optical photometry and find that the optical data do not detect 43% and misidentify an additional 11% of the total AGB population, likely because of extinction caused by circumstellar material. Further, we find that a narrowband optical carbon star study of IC 1613 detects 50% of the total AGB population and only considers 18% of this population in calculating the carbon to M-type AGB ratio. We derive an integrated mass-loss rate from the AGB stars of 0.2-1.0 x 10^(-3) solar masses per year and find that the distribution of bolometric luminosities and mass-loss rates are consistent with those for other nearby metal-poor galaxies. Both the optical completeness fractions and mass-loss rates in IC 1613 are very similar to those in the Local Group dwarf irregular, WLM, which is expected given their similar characteristics and evolutionary histories.