Globular cluster candidates in the Sagittarius dwarf galaxy

TL;DR

This study analyzes newly discovered Sagittarius dwarf galaxy globular clusters using Gaia and SDSS data, revealing their ages, metallicities, and implications for the galaxy's formation and accretion history.

Contribution

It provides a detailed analysis of eight new Sgr globular clusters, including their ages, metallicities, and spatial distributions, enhancing understanding of Sgr's cluster population and formation history.

Findings

Minni 332 is younger and more metal-rich than M54.

The cluster frequency aligns with Sgr's star formation history.

Adding new clusters alters the perceived cluster formation timeline.

Abstract

Recently, new Sagittarius (Sgr) dwarf galaxy globular clusters were discovered, which opens the question on the actual size of the Sgr globular cluster population, and therefore on our understanding of the Sgr galaxy formation and accretion history onto the Milky Way. Based on Gaia EDR3 and SDSS IV DR16 (APOGEE-2) data sets, we performed an analysis of the color-magnitude diagrams (CMDs) of the eight new Sgr globular clusters found by from a sound cleaning of the contamination of Milky Way and Sgr field stars, complemented by Minniti et al. (2021b) available kinematic and metal abundance information. The cleaned CMDs and spatial stellar distributions reveal the presence of stars with a wide range of cluster membership probabilities. Minni 332 turned out to be a younger (< 9 Gyr) and more metal-rich ([M/H] > -1.0 dex) globular cluster than M54, the nuclear Sgr globular cluster, as could also be the case of Minni 342, 348, and 349, although their results are less convincing. Minni 341 could be an open cluster candidate (age < 1 Gyr, [M/H] ~ -0.3 dex), while the analyses of Minni 335, 343, and 344 did not allow us to confirm their physical reality. We also built the Sgr cluster frequency (CF) using available ages of the Sgr globular clusters and compared it with that obtained from the Sgr star formation history. Both CFs are in excellent agreement. However, the addition of eight new globular clusters with ages and metallicities distributed according to the Sgr age-metallicity relationship turns out in a remarkably different CF.