Detection of a population of carbon-enhanced metal-poor stars in the Sculptor dwarf spheroidal galaxy

TL;DR

This study identifies and characterizes carbon-enhanced metal-poor stars in the Sculptor dwarf galaxy, revealing a high fraction of such stars similar to the Milky Way halo, which informs galaxy formation models.

Contribution

First measurement of carbon-enhanced metal-poor stars in Sculptor, showing their prevalence and properties, and comparing them to halo stars to understand galaxy assembly.

Findings

36% CEMP fraction below [Fe/H] = -3.0 in Sculptor

Similar CEMP fraction in Sculptor and the Milky Way halo

No CEMP stars with extreme carbon enhancement detected

Abstract

The study of the chemical abundances of metal-poor stars in dwarf galaxies provides a venue to constrain paradigms of chemical enrichment and galaxy formation. Here we present metallicity and carbon abundance measurements of 100 stars in Sculptor from medium-resolution (R ~ 2000) spectra taken with the Magellan/Michigan Fiber System mounted on the Magellan-Clay 6.5m telescope at Las Campanas Observatory. We identify 24 extremely metal-poor star candidates ([Fe/H] < -3.0) and 21 carbon-enhanced metal-poor (CEMP) star candidates. Eight carbon-enhanced stars are classified with at least 2$\sigma$ confidence and five are confirmed as such with follow-up R~6000 observations using the Magellan Echellette Spectrograph on the Magellan-Baade 6.5m telescope. We measure a CEMP fraction of 36% for stars below [Fe/H] = -3.0, indicating that the prevalence of carbon-enhanced stars in Sculptor is similar to that of the halo (~43%) after excluding likely CEMP-s and CEMP-r/s stars from our sample. However, we do not detect that any CEMP stars are strongly enhanced in carbon (e.g., [C/Fe] > 1.0). The existence of a large number of CEMP stars both in the halo and in Sculptor suggests that some halo CEMP stars may have originated from accreted early analogs of dwarf galaxies.