New constraints on the chemical evolution of the dwarf spheroidal galaxy LeoI from VLT spectroscopy

TL;DR

This study uses VLT spectroscopy of red giant stars in LeoI to refine its chemical evolution history, revealing a narrow metallicity distribution, a shallow gradient, and recent enrichment trends.

Contribution

It provides new spectroscopic metallicity measurements and age-metallicity relations for LeoI, improving understanding of its chemical enrichment history.

Findings

Narrow metallicity distribution with mean [M/H]~-1.2

Shallow metallicity gradient of -0.27 dex/Kpc

Recent increase of ~0.2 dex in metallicity over last few Gyr

Abstract

(Abridged) We present the spectroscopy of red giant stars in the dwarf spheroidal galaxy LeoI, aimed at further constraining its chemical enrichment history. Intermediate-resolution spectroscopy in the CaII triplet spectral region was obtained for 54 stars in LeoI using FORS2 at the ESO Very Large Telescope. The equivalent widths of CaII triplet lines were used to derive the metallicities of the target stars on the [Fe/H] scale of Carretta & Gratton, as well as on a scale tied to the global metal abundance, [M/H]. The metallicity distribution function for LeoI stars is confirmed to be very narrow, with mean value [M/H]~-1.2 and intrinsic dispersion, sigma_[M/H]=0.08. We find a few metal-poor stars (whose metallicity values depend on the adopted extrapolation of the existing calibrations), but in no case are stars more metal-poor than [Fe/H]=-2.6. Our measurements provide a hint of a shallow metallicity gradient of -0.27 dex/Kpc among LeoI red giants. By combining the metallicities of the target stars with their photometric data, we provide age estimates and an age-metallicity relation for a subset of red giant stars in LeoI. Our age estimates indicate a rapid initial enrichment, a slowly rising metal abundance and an increase of ~0.2 dex in the last few Gyr.