Near-Infrared Stellar Populations in the metal-poor, Dwarf irregular Galaxies Sextans A and Leo A

TL;DR

This study investigates near-infrared stellar populations in the metal-poor dwarf irregular galaxies Leo A and Sextans A, revealing significant dust production by evolved stars and challenging previous models of dust formation at low metallicity.

Contribution

It provides new observational evidence of dust formation in metal-poor environments and identifies a substantial dust injection rate from evolved stars in these galaxies.

Findings

Detected red giant and AGB stars indicating intermediate-age populations.

Identified 32 stars in Leo A and 101 in Sextans A with high dust-production rates.

Found evidence for oxygen-rich dust formation at low metallicity, contradicting previous models.

Abstract

We present JHK$_{s}$ observations of the metal-poor ([Fe/H] $<$ -1.40) Dwarf-irregular galaxies, Leo A and Sextans A obtained with the WIYN High-Resolution Infrared Camera at Kitt Peak. Their near-IR stellar populations are characterized by using a combination of colour-magnitude diagrams and by identifying long-period variable stars. We detected red giant and asymptotic giant branch stars, consistent with membership of the galaxy's intermediate-age populations (2-8 Gyr old). Matching our data to broadband optical and mid-IR photometry we determine luminosities, temperatures and dust-production rates (DPR) for each star. We identify 32 stars in Leo A and 101 stars in Sextans A with a DPR $>10^{-11}$ $M_\odot \,{\rm yr}^{-1}$, confirming that metal-poor stars can form substantial amounts of dust. We also find tentative evidence for oxygen-rich dust formation at low metallicity, contradicting previous models that suggest oxygen-rich dust production is inhibited in metal-poor environments. The total rates of dust injection into the interstellar medium of Leo A and Sextans A are (8.2 $\pm$ 1.8) $\times 10^{-9}$ $M_\odot \,{\rm yr}^{-1}$ and (6.2 $\pm$ 0.2) $\times 10^{-7}$ $M_\odot \,{\rm yr}^{-1}$, respectively. The majority of this dust is produced by a few very dusty evolved stars, and does not vary strongly with metallicity.