Probing the early chemical evolution of the Sculptor dSph with purely old stellar tracers

TL;DR

This study uses photometric data of RR Lyrae stars to analyze the early chemical evolution and metallicity distribution of the Sculptor dwarf spheroidal galaxy, revealing a broad metallicity spread and spatial gradients.

Contribution

First detailed photometric analysis of Sculptor's early chemical evolution using RR Lyrae stars, providing new insights into metallicity distribution and gradients without spectroscopic data.

Findings

Broad metallicity distribution peaked at [Fe/H] ≈ -1.90 dex

Metallicity gradient traced out to 55 arcmin, consistent with spectroscopic data

Central regions show no gradient, indicating different stellar populations

Abstract

We present the metallicity distribution of a sample of 471 RR Lyrae (RRL) stars in the Sculptor dSph, obtained from the $I$-band Period-Luminosity relation. It is the first time that the early chemical evolution of a dwarf galaxy is characterized in such a detailed and quantitative way, using photometric data alone. We find a broad metallicity distribution (FWHM=0.8 dex) that is peaked at [Fe/H]$\simeq$-1.90 dex, in excellent agreement with literature values obtained from spectroscopic data. Moreover, we are able to directly trace the metallicity gradient out to a radius of $\sim$55 arcmin. We find that in the outer regions (r$>\sim$32 arcmin) the slope of the metallicity gradient from the RRLs (-0.025 dex arcmin$^{-1}$) is comparable to the literature values based on red giant (RG) stars. However, in the central part of Sculptor we do not observe the latter gradients. This suggests that there is a more metal-rich and/or younger population in Sculptor that does not produce RRLs. This scenario is strengthened by the observation of a metal-rich peak in the metallicity distribution of RG stars by other authors, which is not present in the metallicity distribution of the RRLs within the same central area.