Quantitative Spectroscopy of Supergiants in the Local Group Dwarf Galaxy IC 1613: Metallicity and Distance

TL;DR

This study analyzes blue supergiant stars in IC 1613 to determine their metallicity distribution and uses the FGLR method to measure the galaxy's distance, revealing varied chemical histories and consistent distance estimates.

Contribution

It provides the first bi-modal metallicity distribution of supergiants in IC 1613 and applies the FGLR method for accurate distance measurement.

Findings

Bi-modal metallicity distribution with peaks at -0.50 and -0.85 dex.

Correlation between metallicity and spatial location within IC 1613.

Distance modulus of 24.39 ± 0.11 mag consistent with other methods.

Abstract

We present the spectral analysis of 21 blue supergiant stars of spectral type late B to early A within the Local Group dwarf galaxy IC 1613 based on VLT-FORS2 low resolution spectra. Combining our results with studies of early B type blue supergiants we report a wide bi-modal distribution of metallicities with two peaks around [Z] $\sim -0.50$ dex and [Z] $\sim -0.85$ dex. The bi-modal distribution correlates with spatial location, when compared with column densities of neutral hydrogen in IC 1613. While the low [Z] objects appear in regions of relatively high ISM HI column densities or close to them, the high [Z] supergiants are found in the central HI hole almost devoid of hydrogen. This suggests varied chemical evolution histories of the young stellar populations in IC 1613. Utilizing the Flux-Weighted Gravity-Luminosity Relation (FGLR), we determine IC 1613's distance modulus as $m - M$ = 24.39 $\pm$ 0.11 mag. This value is in agreement within previous distance measurements using the near-infrared period-luminosity relationship of Cepheids and the tip of the red giant branch.